Re: EN60950 protective conductor test (was Re: Circuit Breaker Tripping Dring Fault Tests)

[peter merguerian]

Dear Friends,

Thanks very much to the input regarding CB Tripping During Fault Testing.
There were many thoughts on the subject and I am sure that next time the wall
CB trips during fault tests at your third part certification laboratory, you
have something to talk about - make sure they do not charge you for the
discussion time!

Peter




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Re: EN60950 protective conductor test (was Re: Circuit Breaker Tripping Dring Fault Tests)

[Rich Nute]

Hi Peter:


My comments were based on the proposed requirement to
test the PE path with the circuit prospective current
transient, e.g. 200 amps from a 10,000-amp source for 
the period of time required to operate the overcurrent 
device  -- say less than a second or so.

(The 200 amps is a function of the contact resistances 
and the wire resistances, independent of the fault; 
the duration is a function of the overcurrent device.
200 amps is a reasonable number for plug-and-socket
cord-connected products.)

In order to get this maximum current, the fault must
be near zero ohms for the duration of the current
transient.  

To achieve near-zero ohms, the fault must be a large-
area fault.  A small-area fault is likely to fuse
open due to the current density and resistance at the
contact.

(I had the unfortunate experience that such a test by
a cert house used a small-area contact at a point where
no basic insulation fault could occur; the PWB PE path
was destroyed.  We repeated the test at a large-area
contact where basic insulation could fault, and the
PWB PE path passed.)

>   What if the over current device operates, the earthing path
>   is compromised by the fault, but not destroyed?  

I believe this is the objective of the proposal -- to
test the PE path with the circuit prospective current.
I would expect the compliance criterion to be no damage 
to the PE path.

>   What if the fault is of nonnear-zero impedance, the earthing
>   path is damaged, but not opened, and resetting of the
>   breaker does occur, but at some point the breaker holds due
>   to the relatively high impedance?

This scenario moves from withstanding the circuit 
prospective current to withstanding the steady-state
current just below the operating point of the over-
current device.  

I suggest that this is the objective of the existing 
requirement to test at twice the overcurrent device
rating or 25 amps, whichever is less.

>   a relatively complex earthing path, I have prepared a
>   separate e-mail that includes some construction details and
>   empirical data for a product in my lab.  To be sent soon.

I appreciate you sharing this data.


Best regards,
Rich






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RE: EN60950 protective conductor test (was Re: Circuit Breaker Tripping Dring Fault Tests)

[Peter L. Tarver]

This thread has been largely theoretical.  Let's look at
some empirical test results for a product I just completed
testing.

The product has a redundant power configuration and nearly
identical current paths for each of two power supplies,
though one has about 2 in. longer traces on one side of one
of the boards involved.  There is no supplementary
overcurrent protection between the appliance inlets and the
input connections of the power supplies.

The earthing path involves the following:

filtered appliance inlet -->
quick-disconnect on filter -->
~1.5 in. No. 18 AWG terminated in a ring lug -->
earthing stackup on a PEM stud of ring lug (from filter),
KEPS nut, ring lug for downstream earthing, KEPS nut -->
~15 in. No. 18 AWG to a header style, soldered through-hole
interconnect -->
traces -->
soldered through-hole interconnect (for hot swappable power
supply) -->
soldered through-hole interconnect -->
traces -->
soldered through-hole to a header style, interconnect -->
~9 in. No. 18 AWG -->
soldered through-hole to a header style, interconnect on the
power supply -->
internal power supply magic -->
large, open-frame heatsink on power supply

This testing was first performed in situ and as intended in
normal use.  I believe this test configuration should be
used for the purposes of safety certification.

In each of the following cases, the earthing impedance test
current was maintained for 2 minutes.  These tests were
performed "precompliance."

I first tested the shortest path.

before faulting test current: 20.0 A
after faulting test current: 20.4 A

before faulting: 0.008 Ohm (a 0.016 V drop across the path)
after faulting: 0.006 Ohm (a 0.012 V drop across the path)

Surprising to have a lower impedance final result.  So much
so, I assumed I must have done something incorrectly,
reflowed a bad solder joint, initiated metal migration ...
something, either during the fault test, the earthing
impedance test or both.

Based on the product's construction, I knew that some
incidental current paths contributed to the very low
earthing impedance.  I then removed the assemblies of
interest from the main chassis and retested on the other of
the two circuits, so that only the current path of specific
interest was involved.  I left the main protective earthing
connection intact on the chassis.  Testing the longest path,

before faulting test current: 20.5 A
after faulting test current: 20.4 A

before faulting: 0.038 Ohm (a 0.77 V drop across the path)
after faulting: 0.037 Ohm (a 0.75 V drop across the path)

Still compliant at a ~20 A current value and still an
apparent *reduction* in the impedance of the earthing path.
This is not coincidence and double checking my test methods
along the way told me there were no errors.

I performed a third test on the same sample, longest path,
still outside the enclosure.

before faulting test current: 20.4 A
after faulting test current: 30.2 A

before faulting: 0.036 Ohm (a 0.74 V drop across the path)
after faulting: 0.041 Ohm (a 1.24 V drop across the path)


The above testing was repeated in situ on a new test sample.
The earthing impedance test, before and after, was set to 40
A.  The results were very similar to those for the first in
situ test, with almost identical calculated impedances, and
the earthing path withstood the 40 A current very nicely.

It should be noted that I performed the fault on a 120V, 20
A branch circuit.  The product will be rated for 240 V and
CSA 22.2 No. 0.4 requires the test be performed on a circuit
with the voltage at the highest rating marked on the
product, but I only have 20 A circuits on 120V circuits; my
208 V circuits, which I can boost to 240V, are all 30 A.


Regards,

Peter L. Tarver, PE
Product Safety Manager
Sanmina-SCI Homologation Services
San Jose, CA
peter.tar...@sanmina-sci.com





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RE: EN60950 protective conductor test (was Re: Circuit Breaker Tripping Dring Fault Tests)

[Peter L. Tarver]

> From: Rich Nute
> Sent: Wednesday, February 05, 2003 12:20 PM
>
> Hi Peter:

Hi, Rich.

> This test implies a near 0-ohm fault to the
> PE, where the PE circuit includes a PE trace
> on the PWB.

That's a reasonable assumption and is convenient for the
purposes of testing.  It is unlikely to be the only fault
case, but that's irrelevant to compliance with the standard
and should be considered internally, to the level of pain
tolerable by any particular company.

> If there is a zero-ohm fault, an over-current
> device, somewhere, will operate.  (Indeed, this
> is the function of the PE circuit!)  A zero-ohm
> fault implies a large-area contact with a fair
> amount of contact pressure for at least the
> period of time to operate the overcurrent device.
>
> Consequently, the product must be removed from
> service and repaired before being returned to
> service.

What if the over current device operates, the earthing path
is compromised by the fault, but not destroyed?  Let us not
forget that there are many who will reset a circuit breaker
ad infinitum, to failure, reimposing a fault repeatedly.  (I
spoke this afternoon to a coworker who is also landlord.
One tenant consistently overloaded a branch circuit and
reset the circuit breaker repeatedly, until it failed to
close.)

Each resetting of the circuit imposes a similar fault, with
a progressively weaker earthing circuit.  Let us assume that
at some point short of circuit breaker failure, the earthing
path becomes compromised enough that the branch circuit does
not open the circuit.

What if the fault is of nonnear-zero impedance, the earthing
path is damaged, but not opened, and resetting of the
breaker does occur, but at some point the breaker holds due
to the relatively high impedance?

We can let our imaginations wander from there and each
believe as we will that thus and such will or will not,
could or could not happen and debate the probabilities until
the ruminants return hither.  Bad stuff happens: dead-front
switchboards explode, fires are started by minor appliances
with safety certification house marks or questionable wiring
practices, trains jump the tracks...


> If the 0-ohm fault is on the PWB, then the PWB
> will need to be replaced.  It is difficult to
> imagine a fault of 0-ohm proportions that could
> be repaired without replacing the PWB assembly.
> Indeed, if the PWB PE circuit carries the high
> transient current, it may very well be that the
> supply conductors on the PWB may be blown off
> the PWB.  So, I question whether the compliance
> criteria need be applied.

If.  The fault might occur anywhere in the earthing path.
To give an idea of how a relatively simple idea can lead to
a relatively complex earthing path, I have prepared a
separate e-mail that includes some construction details and
empirical data for a product in my lab.  To be sent soon.


> >   There is also the much more variable solder
> in the earthing
> >   path.  While manufacturing techniques have
> come a long way
> >   in terms of consistency, the amount of solder
> in a joint and
> >   the quality of the joint itself can play a
> significant role.
> >   It should be expected that a lower melting
> point solder will
> >   perform less well than a higher melting point solder.
> >   Appropriate process controls will have a
> positive effect.
>
> An ideal solder joint involves an amalgam at
> the joint with the conductors.  The properties
> of the amalgam are typically "greater" than
> the property of either material alone.  As in
> copper plumbing joints, an idea joint has very
> little solder between the two components being
> joined.

And yet, mass production of electrical and electronic
products, while generally yielding consistent-quality
products when produced in a conscientious environment, can
still have variability and initially undetectable problems
that even HALT testing can't predict and HASS testing can't
weed out.  There will be very few companies with zero field
returns where cracks develop in a laminate, solder joints
fail or are imperfect to the point of eventually some flaw
eventually rears its head.

The goal is to at least offer the impression that a
construction will not yield an insidious hazard at some
point in the future.  My recent experience has led me to
believe that, aside from a few head scratching results, the
test is *very* simple to perform and requires almost *no*
additional test equipment, over and above an earthing
impedance test setup and a modicum of ingenuity inherent in
any engineer.

> My guess would be that the current path will be
> that of least resistance, which will minimize
> the current through the solder around the joint.
> So, I would doubt that the solder (of a good
> joint) would be much affected by the current
> pulse.
>
>
> Best regards,
> Rich

There's no question that incidental currents can have a
positive effect, even if not considered "reliable."  There's
no denying that it is possible to comply with the 

Re: EN60950 protective conductor test (was Re: Circuit Breaker Tripping Dring Fault Tests)

[Rich Nute]

Hi Peter:


>   Not quite.  I^2·t will tell you the let through current of
>   the copper trace, but will not necessarily tell you if the
>   construction will be compliant.  The compliance criteria for
>   this test include:
>   
>   * no damage to the trace (no lifting, probably no
>   discoloration)
>   * no damage to the PWB (no delamination, burning; I don't
>   know if this includes burning off of solder mask)
>   * before and after earthing impedance must comply with the
>   0.1 Ohm maximum impedance
>   * no change in earthing impedance greater than 10% of the
>   before and after earthing impedance results

This test implies a near 0-ohm fault to the
PE, where the PE circuit includes a PE trace 
on the PWB.

If there is a zero-ohm fault, an over-current
device, somewhere, will operate.  (Indeed, this
is the function of the PE circuit!)  A zero-ohm
fault implies a large-area contact with a fair
amount of contact pressure for at least the 
period of time to operate the overcurrent device.

(A point-contact fault would blow a hole in the
copper trace due to very high current density
at the point of contact.)

Consequently, the product must be removed from
service and repaired before being returned to
service.

If the 0-ohm fault is on the PWB, then the PWB
will need to be replaced.  It is difficult to
imagine a fault of 0-ohm proportions that could
be repaired without replacing the PWB assembly.
Indeed, if the PWB PE circuit carries the high
transient current, it may very well be that the
supply conductors on the PWB may be blown off
the PWB.  So, I question whether the compliance 
criteria need be applied.

>   There is also the much more variable solder in the earthing
>   path.  While manufacturing techniques have come a long way
>   in terms of consistency, the amount of solder in a joint and
>   the quality of the joint itself can play a significant role.
>   It should be expected that a lower melting point solder will
>   perform less well than a higher melting point solder.
>   Appropriate process controls will have a positive effect.

An ideal solder joint involves an amalgam at 
the joint with the conductors.  The properties
of the amalgam are typically "greater" than 
the property of either material alone.  As in
copper plumbing joints, an idea joint has very
little solder between the two components being
joined.

My guess would be that the current path will be
that of least resistance, which will minimize
the current through the solder around the joint.
So, I would doubt that the solder (of a good
joint) would be much affected by the current
pulse.


Best regards,
Rich





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Re: EN60950 protective conductor test (was Re: Circuit Breaker Tripping Dring Fault Tests)

[Rich Nute]

Hi Chris:


>   It seems funny to me that most equipment has been historically made with
18AWG protective ground pigtail wires; and 25A ground fault tests have been
used for years.  
>   
>   Now that PC  traces are being used for protective ground; we want to test
with 200A or greater impulse currents?  I'm curious about what would happen to
your typical 18AWG line cord during this test.  I'm wondering if the line cord
would fuse open? 

The 18 AWG readily passes the circuit prospective
current test.  This is because the current is
transient, and is cut off before the wire in the 
cord can reach fusing temperature.

>   One is at www.kepcopower.com/nomovax2.htm this is a nomograph of maximum
operating current, AWG and IR drop in the conductor.  The point "A" is
generally considered the point of maximum IR drop.  If you draw a line from
point "A", through a wire gauge size; you'll get a max current.  Of course
this is steady state current; and the nomograph assumes a single wire.  Wire
bundles would be a worse case.  It's too bad that this chart doesn't contain
the "fuse" values for the wires as well (the  I squared * T values).

Fusing currents for wires are published in:

Reference Data for Radio Engineers
International Telephone and Telegraph Corporation
67 Broad Street
New York 4, New York

This reference says "Courtesy of Automatic 
Electric Company, Chicago, Illinois."

The approximate fusing current for 18 AWG copper 
is 82.9 amperes.

The approximate fusing current of wires can be 
calculated from:

I  =  (K) * (d**3/2)

where d is the diameter of the wire, in inches
  K is a constant that depends on the metal

Here are some values for K:

copper:10,244
aluminum:   7,585
silver: 5,230
iron:   3,148
tin:1,642

The "Standard Handbook for Electrical Engineers"
by Fink and Beatty has some additional data,
including curves of current and time for each
AWG.  A couple of points for 18 AWG:

   0.1 second:~720 amps
   1.0 second:~220 amps
  10.0 second:~ 82 amps
   
>   3.  The third problem is mechanical.  Once Earth ground brought to a pad
on the circuitboard; then there is still the issue of getting a good
mechanical mate to the chassis with a wide surface area.  If the connection is
made through a couple of teeth on a star washer; then there is a potential for
localized heating.   I'm just going to maximize surface contact area for this
one.  I'm also considering using multiple board to chassis connection
locations.  Every screw that connects the board to chassis is a potential
Earth ground connection.

The problem with mechanical connections to PWBs 
by means of screws is that the PWB base material 
is a plastic and is subject to cold-flow under 
compressive conditions.  In the long-term, the
connection can loosen.  

Not everyone pays attention to this, and, in 
practice, it is rarely a problem.

One way around this is to use a wire from the 
board to the chassis.


Best regards,
Rich






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RE: EN60950 protective conductor test (was Re: Circuit Breaker Tripping Dring Fault Tests)

[Gary McInturff]

Lou,
I'm not proposing anything mind you, but you could save some space if 
you had
a PWB mounted appliance inlet and you would still have to get the PEC to the
chassis. 
Gary


From: Lou Aiken [mailto:ai...@gulftel.com]
Sent: Tuesday, February 04, 2003 8:36 AM
To: Peter L. Tarver; emc-p...@majordomo.ieee.org
Subject: Re: EN60950 protective conductor test (was Re: Circuit Breaker
Tripping Dring Fault Tests)



Why not provide a fuse to prevent deterioration of the PE trace on a PCB?

Joking of course, but now that I have your attention, I would like to see
this thread move away from the physics and discuss what practical reasons
there are for using PC traces to provide earth fault circuits.


Lou Aiken, LaMer LLC
27109 Palmetto Drive
Orange Beach, AL
36561 USA

tel ++ 1 251 981 6786
fax ++ 1 251 981 3054
Cell ++ 1 251 979 4648

From: Peter L. Tarver 
To: 
Sent: Tuesday, February 04, 2003 9:53 AM
Subject: RE: EN60950 protective conductor test (was Re: Circuit Breaker
Tripping Dring Fault Tests)



Not quite.  I^2·t will tell you the let through current of
the copper trace, but will not necessarily tell you if the
construction will be compliant.  The compliance criteria for
this test include:

* no damage to the trace (no lifting, probably no
discoloration)
* no damage to the PWB (no delamination, burning; I don't
know if this includes burning off of solder mask)
* before and after earthing impedance must comply with the
0.1 Ohm maximum impedance
* no change in earthing impedance greater than 10% of the
before and after earthing impedance results

There is also the much more variable solder in the earthing
path.  While manufacturing techniques have come a long way
in terms of consistency, the amount of solder in a joint and
the quality of the joint itself can play a significant role.
It should be expected that a lower melting point solder will
perform less well than a higher melting point solder.
Appropriate process controls will have a positive effect.

These are some of the reasons some form of safety agency
factory auditing of this type of construction is normal.


Regards,

Peter L. Tarver, PE
Product Safety Manager
Sanmina-SCI Homologation Services
San Jose, CA
peter.tar...@sanmina-sci.com


> -Original Message-
> From: Chris Maxwell
> Sent: Tuesday, February 04, 2003 5:32 AM
>
>
> Exactly!
>
> Chris Maxwell
>
>
> > -Original Message-
> > From: drcuthbert [SMTP:drcuthb...@micron.com]
> > Sent: Monday, February 03, 2003 7:50 PM
> >
> > What is needed is the I squared t rating of the
> breaker. Then the (I^2)(t)
> > rating of the PCB. Then you know if the PCB can
> take it.
> >
> >Dave Cuthbert



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RE: EN60950 protective conductor test (was Re: Circuit Breaker Tripping Dring Fault Tests)

[Chris Maxwell]

PC traces are easier to assemble and the assembly can be done in a tighter
space.  I think (just an opinion)  that proper design could make this type of
system more reliable as well with less chances of wires coming loose...

> -Original Message-
> From: Lou Aiken [SMTP:ai...@gulftel.com]
> Sent: Tuesday, February 04, 2003 11:36 AM
> To:   Peter L. Tarver; emc-p...@majordomo.ieee.org
> Subject:  Re: EN60950 protective conductor test (was Re: Circuit Breaker
Tripping Dring Fault Tests)
> 
> 
> Why not provide a fuse to prevent deterioration of the PE trace on a PCB?
> 
> Joking of course, but now that I have your attention, I would like to see
> this thread move away from the physics and discuss what practical reasons
> there are for using PC traces to provide earth fault circuits.
> 
> 
> Lou Aiken, LaMer LLC
> 27109 Palmetto Drive
> Orange Beach, AL
> 36561 USA
> 
> tel ++ 1 251 981 6786
> fax ++ 1 251 981 3054
> Cell ++ 1 251 979 4648
> - Original Message -
> From: Peter L. Tarver 
> To: 
> Sent: Tuesday, February 04, 2003 9:53 AM
> Subject: RE: EN60950 protective conductor test (was Re: Circuit Breaker
> Tripping Dring Fault Tests)
> 
> 
> 
> Not quite.  I^2·t will tell you the let through current of
> the copper trace, but will not necessarily tell you if the
> construction will be compliant.  The compliance criteria for
> this test include:
> 
> * no damage to the trace (no lifting, probably no
> discoloration)
> * no damage to the PWB (no delamination, burning; I don't
> know if this includes burning off of solder mask)
> * before and after earthing impedance must comply with the
> 0.1 Ohm maximum impedance
> * no change in earthing impedance greater than 10% of the
> before and after earthing impedance results
> 
> There is also the much more variable solder in the earthing
> path.  While manufacturing techniques have come a long way
> in terms of consistency, the amount of solder in a joint and
> the quality of the joint itself can play a significant role.
> It should be expected that a lower melting point solder will
> perform less well than a higher melting point solder.
> Appropriate process controls will have a positive effect.
> 
> These are some of the reasons some form of safety agency
> factory auditing of this type of construction is normal.
> 
> 
> Regards,
> 
> Peter L. Tarver, PE
> Product Safety Manager
> Sanmina-SCI Homologation Services
> San Jose, CA
> peter.tar...@sanmina-sci.com
> 
> 
> > -Original Message-
> > From: Chris Maxwell
> > Sent: Tuesday, February 04, 2003 5:32 AM
> >
> >
> > Exactly!
> >
> > Chris Maxwell
> >
> >
> > > -Original Message-
> > > From: drcuthbert [SMTP:drcuthb...@micron.com]
> > > Sent: Monday, February 03, 2003 7:50 PM
> > >
> > > What is needed is the I squared t rating of the
> > breaker. Then the (I^2)(t)
> > > rating of the PCB. Then you know if the PCB can
> > take it.
> > >
> > >Dave Cuthbert
> 
> 
> ---
> This message is from the IEEE EMC Society Product Safety
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Re: EN60950 protective conductor test (was Re: Circuit Breaker Tripping Dring Fault Tests)

[John Barnes]

Chris,
Douglas Brooks wrote an article about Preese's and Onderdonk's equations
for fusing currents of wires, which was published in Printed Circuit
Magazine.  It can be downloaded from UltraCAD's web site at
http://www.ultracad.com/fusing.pdf

Appendix F of the book that I am writing for Kluwer, Robust Electronic
Design Reference, will cover the ampacity (current-carrying capacity) of
wires, printed circuit board traces, busbars, etc.  The manuscript is
due August 1st, so I had better get back to my writing...

John Barnes KS4GL, PE, NCE, ESDC Eng, SM IEEE
dBi Corporation
http://www.dbicorporation.com/


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Re: EN60950 protective conductor test (was Re: Circuit Breaker Tripping Dring Fault Tests)

[John Woodgate]

I read in !emc-pstc that Chris Maxwell  wrote
(in <83d652574e7af740873674f9fc12dbaaf7e...@utexh1w2.gnnettest.com>)
about 'EN60950 protective conductor test (was Re: Circuit Breaker
Tripping Dring Fault Tests)' on Tue, 4 Feb 2003:

>This would make heat dissipation different; and I would assume that it would 
>make the fusing characteristics (I^2)(t) slightly different as well.

Or even a lot different. The reason why I personally would not use a
printed board trace as a PEC is that boards can develop cracks and thin
copper patches, so I couldn't guarantee that every board would stand the
test that the test sample passed. In this case, I don't think
potentially destructive sample testing is adequate, either. The PEC
needs to be 'four nines' reliable.
-- 
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk 
Interested in professional sound reinforcement and distribution? Then go to 
http://www.isce.org.uk
PLEASE do NOT copy news posts to me by E-MAIL!


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Re: EN60950 protective conductor test (was Re: Circuit Breaker Tripping Dring Fault Tests)

[Lou Aiken]

Why not provide a fuse to prevent deterioration of the PE trace on a PCB?

Joking of course, but now that I have your attention, I would like to see
this thread move away from the physics and discuss what practical reasons
there are for using PC traces to provide earth fault circuits.


Lou Aiken, LaMer LLC
27109 Palmetto Drive
Orange Beach, AL
36561 USA

tel ++ 1 251 981 6786
fax ++ 1 251 981 3054
Cell ++ 1 251 979 4648

From: Peter L. Tarver 
To: 
Sent: Tuesday, February 04, 2003 9:53 AM
Subject: RE: EN60950 protective conductor test (was Re: Circuit Breaker
Tripping Dring Fault Tests)



Not quite.  I^2·t will tell you the let through current of
the copper trace, but will not necessarily tell you if the
construction will be compliant.  The compliance criteria for
this test include:

* no damage to the trace (no lifting, probably no
discoloration)
* no damage to the PWB (no delamination, burning; I don't
know if this includes burning off of solder mask)
* before and after earthing impedance must comply with the
0.1 Ohm maximum impedance
* no change in earthing impedance greater than 10% of the
before and after earthing impedance results

There is also the much more variable solder in the earthing
path.  While manufacturing techniques have come a long way
in terms of consistency, the amount of solder in a joint and
the quality of the joint itself can play a significant role.
It should be expected that a lower melting point solder will
perform less well than a higher melting point solder.
Appropriate process controls will have a positive effect.

These are some of the reasons some form of safety agency
factory auditing of this type of construction is normal.


Regards,

Peter L. Tarver, PE
Product Safety Manager
Sanmina-SCI Homologation Services
San Jose, CA
peter.tar...@sanmina-sci.com


> -Original Message-
> From: Chris Maxwell
> Sent: Tuesday, February 04, 2003 5:32 AM
>
>
> Exactly!
>
> Chris Maxwell
>
>
> > -Original Message-
> > From: drcuthbert [SMTP:drcuthb...@micron.com]
> > Sent: Monday, February 03, 2003 7:50 PM
> >
> > What is needed is the I squared t rating of the
> breaker. Then the (I^2)(t)
> > rating of the PCB. Then you know if the PCB can
> take it.
> >
> >Dave Cuthbert



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RE: EN60950 protective conductor test (was Re: Circuit Breaker Tripping Dring Fault Tests)

[Peter L. Tarver]

Not quite.  I^2·t will tell you the let through current of
the copper trace, but will not necessarily tell you if the
construction will be compliant.  The compliance criteria for
this test include:

* no damage to the trace (no lifting, probably no
discoloration)
* no damage to the PWB (no delamination, burning; I don't
know if this includes burning off of solder mask)
* before and after earthing impedance must comply with the
0.1 Ohm maximum impedance
* no change in earthing impedance greater than 10% of the
before and after earthing impedance results

There is also the much more variable solder in the earthing
path.  While manufacturing techniques have come a long way
in terms of consistency, the amount of solder in a joint and
the quality of the joint itself can play a significant role.
It should be expected that a lower melting point solder will
perform less well than a higher melting point solder.
Appropriate process controls will have a positive effect.

These are some of the reasons some form of safety agency
factory auditing of this type of construction is normal.


Regards,

Peter L. Tarver, PE
Product Safety Manager
Sanmina-SCI Homologation Services
San Jose, CA
peter.tar...@sanmina-sci.com


> -Original Message-
> From: Chris Maxwell
> Sent: Tuesday, February 04, 2003 5:32 AM
>
>
> Exactly!
>
> Chris Maxwell
>
>
> > -Original Message-
> > From:   drcuthbert [SMTP:drcuthb...@micron.com]
> > Sent:   Monday, February 03, 2003 7:50 PM
> >
> > What is needed is the I squared t rating of the
> breaker. Then the (I^2)(t)
> > rating of the PCB. Then you know if the PCB can
> take it.
> >
> >Dave Cuthbert



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RE: EN60950 protective conductor test (was Re: Circuit Breaker Tripping Dring Fault Tests)

[Chris Maxwell]

Exactly!  There is lots of data and tables available on the web for steady
state current; but I haven't found any sources that would give the (I^2)(t)
values for wires or PCB traces.   Such tables would take a great deal of
mystery out of this subject.  Right now, the best guess is to go by steady
state current rating; but there must be faults in this.  A PCB trace that can
handle 10 Amps of steady state current has a totally different geometry than a
wire that can handle 10 Amps of steady state current.  This would make heat
dissipation different; and I would assume that it would make the fusing
characteristics (I^2)(t) slightly different as well.

Chris Maxwell | Design Engineer - Optical Division
email chris.maxw...@nettest.com | dir +1 315 266 5128 | fax +1 315 797 8024

NetTest | 6 Rhoads Drive, Utica, NY 13502 | USA
web www.nettest.com | tel +1 315 797 4449 | 




> -Original Message-
> From: drcuthbert [SMTP:drcuthb...@micron.com]
> Sent: Monday, February 03, 2003 7:50 PM
> To:   'John Woodgate'; emc-p...@majordomo.ieee.org
> Subject:  RE: EN60950 protective conductor test (was Re: Circuit Breaker
Tripping Dring Fault Tests)
> 
> 
> What is needed is the I squared t rating of the breaker. Then the (I^2)(t)
> rating of the PCB. Then you know if the PCB can take it. 
> 
>Dave Cuthbert
> 
> 


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EN60950 protective conductor test (was Re: Circuit Breaker Tripping Dring Fault Tests)

[John Woodgate]

I read in !emc-pstc that cnew...@xycom.com wrote (in <85256CC2.005F2DA4.
0...@notes.fw.xycom.com>) about 'EN60950 protective conductor test (was
Re: Circuit Breaker      Tripping Dring Fault Tests)' on Mon, 3 Feb
2003:

>My UL guy tells me that I should expect the typical service type CB to be
rated
>up to  + 10%.  So it appears that  I need to concern myself with a burst of
>current
>up to approximately 22 amps for the 20 amp AC circuit that my product is being
>evaluated for.

Until it trips, your CB lets through the **whole 200 A**. The trip
current is practically irrelevant in this test; what matters is the trip
TIME. The board trace may stand 200 A for 50 ms but not for 100 ms.
-- 
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk 
Interested in professional sound reinforcement and distribution? Then go to 
http://www.isce.org.uk
PLEASE do NOT copy news posts to me by E-MAIL!


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RE: EN60950 protective conductor test (was Re: Circuit Breaker Tripping Dring Fault Tests)

[Peter L. Tarver]

I've had extensive discussion with UL regarding the
performance of this test.  Below are my comments, taken from
these discussions.

> -Original Message-
> From: Carl Newton
> Sent: Monday, February 03, 2003 9:20 AM
>
>
> 1.  Three samples are tested;

Intended to demonstrate repeatability of the test results.

> 2.  Trace resistance is measured before and after
> test.  Resistance cannot
>   exceed 0.1 ohms, and cannot change more
> than 10% after test;

The test datasheets I have from UL state the impedance
before and after applying the fault is measured using an
ohmmeter.  I intend to use a lower current version of the
earthing impedance test for this purpose (say, 20A, rather
than 40A).

> 3.  AC source is 240 Vac, 200 amps (20A circuit
> breaker X 10), power factor
>   is 75 - 80% through shorted bus bars with a
> 20/30 A (20 in my case)
> service
>   entrance type circuit breaker in series
> with the testing terminals.  The
> circuit
>   breaker is connected to the bus bars by
> 1.22 m (4 ft.) of #12 AWG wire.

Some of this information is for the UL lab technician, in
order to increase the reproducibility of the results and
protect their equipment.  For instance:

*no power factor is specified in CSA 22.2 No. 0.4
*bus bars are what exist in UL's lab and are not a
requirement to perform this test
*UL's power panels this test is derived from will likely be
capable of very large fault currents, so they will add
resistance to limit the current
*a service entrance circuit breaker is not necessary; this
was chosen for it's larger interrupting rating, so as to not
degrade the breaker too quickly under repeated fault
conditions; you can use a plain old branch circuit breaker.


> 4.  The test circuit is connected to the DUT via
> the grounding lead of the
>   1.82 m (6 ft) power supply cord.  If cord
> is not provided, then #16 AWG
>   wire is used.

It's anyone's guess why a No. 16

> 5.  Test continues until ultimate results occur;
> e.g. CB trips, trace opens,
> etc.
>
> Carl

The preliminary testing I've performed in my lab indicates
that the fault portion of the test can be over very quickly
(probably ms, but I haven't tried to measure it), even with
No. 18 AWG conductors and four connectorized interfaces
involved.


Regards,

Peter L. Tarver, PE
Product Safety Manager
Sanmina-SCI Homologation Services
San Jose, CA
peter.tar...@sanmina-sci.com



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Re: EN60950 protective conductor test (was Re: Circuit Breaker Tripping Dring Fault Tests)

[cnew...@xycom.com]

Lou,

It's my impression that the typical switching power supply, such as
that  used for ITE type equipment, will apply basic insulation between
the primary circuits and earthed conductive parts on the primary side.
They do this in order to minimize the creepage/clearance requirements
and subsequently reduce the size of the supply.  I'm referring specifically
to Tables 2G and 2F of 60950.

Thanks,
 Carl




From: "Lou Aiken"  on 02/03/2003 01:46 PM

To:   Carl Newton/XYCOM@XYCOM, emc-p...@majordomo.ieee.org
cc:

Subject:  Re: EN60950 protective conductor test (was Re: Circuit Breaker
  Tripping Dring Fault Tests)



Carl, If the primary supply circuitry and components provide double or
reinforced insulation, nothing can become live in the event of a single
fault, the test becomes unnecessary, and I would argue that fact.

If the design does not provide double or reinforced insulation, the test
sounds applicable from points that could become live in case of a basic
insulation fault.

Regards,
Lou Aiken, LaMer LLC
27109 Palmetto Drive
Orange Beach, AL
36561 USA

tel ++ 1 251 981 6786
fax ++ 1 251 981 3054
Cell ++ 1 251 979 4648

From: 
To: 
Sent: Monday, February 03, 2003 11:19 AM
Subject: RE: EN60950 protective conductor test (was Re: Circuit Breaker
Tripping Dring Fault Tests)


>
>
>
> A slight divergence from the EN specifically, but I thought that the
> following would be helpful to this thread:
>
> I am presently working this issue with a UL engineer in accordance with
> UL 60950, 3rd Edition.   I also have the UL 60950 3rd Ed. Test Data
Sheets.
> Their "Protective Earthing Trace Earth Fault Current Test", UL Doc.
190.eng,
> per Section 2.6.3.3 requires the following in my case:
>
> 1.  Three samples are tested;
>
> 2.  Trace resistance is measured before and after test.  Resistance cannot
>   exceed 0.1 ohms, and cannot change more than 10% after test;
>
> 3.  AC source is 240 Vac, 200 amps (20A circuit breaker X 10), power
factor
>   is 75 - 80% through shorted bus bars with a 20/30 A (20 in my case)
> service
>   entrance type circuit breaker in series with the testing terminals.
The
> circuit
>   breaker is connected to the bus bars by 1.22 m (4 ft.) of #12 AWG
wire.
>
> 4.  The test circuit is connected to the DUT via the grounding lead of the
>   1.82 m (6 ft) power supply cord.  If cord is not provided, then #16
AWG
>   wire is used.
>
> 5.  Test continues until ultimate results occur; e.g. CB trips, trace
opens,
> etc.
>
> My UL guy tells me that I should expect the typical service type CB to be
rated
> up to  + 10%.  So it appears that  I need to concern myself with a burst
of
> current
> up to approximately 22 amps for the 20 amp AC circuit that my product is
being
> evaluated for.
>
> Carl
>
>
>
>
>
> From: "Chris Maxwell"  on 02/03/2003 09:29 AM
>
> Please respond to "Chris Maxwell" 
>
> To:   emc-p...@majordomo.ieee.org
> cc:(bcc: Carl Newton/XYCOM)
>
> Subject:  RE: EN60950 protective conductor test (was Re: Circuit Breaker
>   Tripping Dring Fault Tests)
>
>
>
>
> This thread has been interesting.  I am, at this moment, considering a
design
> where I am almost forced to use a PC (printed circuit) trace for Earth
ground.
>
> It seems funny to me that most equipment has been historically made with
18AWG
> protective ground pigtail wires; and 25A ground fault tests have been used
for
> years.
>
> Now that PC  traces are being used for protective ground; we want to test
with
> 200A or greater impulse currents?  I'm curious about what would happen to
your
> typical 18AWG line cord during this test.  I'm wondering if the line cord
would
> fuse open?
>
> There are a couple of handy charts on the web.
>
> One is at www.kepcopower.com/nomovax2.htm this is a nomograph of maximum
> operating current, AWG and IR drop in the conductor.  The point "A" is
generally
> considered the point of maximum IR drop.  If you draw a line from point
"A",
> through a wire gauge size; you'll get a max current.  Of course this is
steady
> state current; and the nomograph assumes a single wire.  Wire bundles
would be a
> worse case.  It's too bad that this chart doesn't contain the "fuse"
values for
> the wires as well (the  I squared * T values).
>
> Another is at www.circuitboards.com/capacity.php3.   This is a chart of
max
> current for PC traces.  Remember that this is for TRACES and planes only;
it
> doesn't say anything about vias and other potential problems.
>
> At first pass, it seems that a trace size to handle twice the power cord's
max
> current, (from the nomograph) with a 10degC trace temperature rise (

Re: EN60950 protective conductor test (was Re: Circuit Breaker Tripping Dring Fault Tests)

[Lou Aiken]

Carl, If the primary supply circuitry and components provide double or
reinforced insulation, nothing can become live in the event of a single
fault, the test becomes unnecessary, and I would argue that fact.

If the design does not provide double or reinforced insulation, the test
sounds applicable from points that could become live in case of a basic
insulation fault.

Regards,
Lou Aiken, LaMer LLC
27109 Palmetto Drive
Orange Beach, AL
36561 USA

tel ++ 1 251 981 6786
fax ++ 1 251 981 3054
Cell ++ 1 251 979 4648

From: 
To: 
Sent: Monday, February 03, 2003 11:19 AM
Subject: RE: EN60950 protective conductor test (was Re: Circuit Breaker
Tripping Dring Fault Tests)


>
>
>
> A slight divergence from the EN specifically, but I thought that the
> following would be helpful to this thread:
>
> I am presently working this issue with a UL engineer in accordance with
> UL 60950, 3rd Edition.   I also have the UL 60950 3rd Ed. Test Data
Sheets.
> Their "Protective Earthing Trace Earth Fault Current Test", UL Doc.
190.eng,
> per Section 2.6.3.3 requires the following in my case:
>
> 1.  Three samples are tested;
>
> 2.  Trace resistance is measured before and after test.  Resistance cannot
>   exceed 0.1 ohms, and cannot change more than 10% after test;
>
> 3.  AC source is 240 Vac, 200 amps (20A circuit breaker X 10), power
factor
>   is 75 - 80% through shorted bus bars with a 20/30 A (20 in my case)
> service
>   entrance type circuit breaker in series with the testing terminals.
The
> circuit
>   breaker is connected to the bus bars by 1.22 m (4 ft.) of #12 AWG
wire.
>
> 4.  The test circuit is connected to the DUT via the grounding lead of the
>   1.82 m (6 ft) power supply cord.  If cord is not provided, then #16
AWG
>   wire is used.
>
> 5.  Test continues until ultimate results occur; e.g. CB trips, trace
opens,
> etc.
>
> My UL guy tells me that I should expect the typical service type CB to be
rated
> up to  + 10%.  So it appears that  I need to concern myself with a burst
of
> current
> up to approximately 22 amps for the 20 amp AC circuit that my product is
being
> evaluated for.
>
> Carl
>
>
>
>
>
> From: "Chris Maxwell"  on 02/03/2003 09:29 AM
>
> Please respond to "Chris Maxwell" 
>
> To:   emc-p...@majordomo.ieee.org
> cc:(bcc: Carl Newton/XYCOM)
>
> Subject:  RE: EN60950 protective conductor test (was Re: Circuit Breaker
>   Tripping Dring Fault Tests)
>
>
>
>
> This thread has been interesting.  I am, at this moment, considering a
design
> where I am almost forced to use a PC (printed circuit) trace for Earth
ground.
>
> It seems funny to me that most equipment has been historically made with
18AWG
> protective ground pigtail wires; and 25A ground fault tests have been used
for
> years.
>
> Now that PC  traces are being used for protective ground; we want to test
with
> 200A or greater impulse currents?  I'm curious about what would happen to
your
> typical 18AWG line cord during this test.  I'm wondering if the line cord
would
> fuse open?
>
> There are a couple of handy charts on the web.
>
> One is at www.kepcopower.com/nomovax2.htm this is a nomograph of maximum
> operating current, AWG and IR drop in the conductor.  The point "A" is
generally
> considered the point of maximum IR drop.  If you draw a line from point
"A",
> through a wire gauge size; you'll get a max current.  Of course this is
steady
> state current; and the nomograph assumes a single wire.  Wire bundles
would be a
> worse case.  It's too bad that this chart doesn't contain the "fuse"
values for
> the wires as well (the  I squared * T values).
>
> Another is at www.circuitboards.com/capacity.php3.   This is a chart of
max
> current for PC traces.  Remember that this is for TRACES and planes only;
it
> doesn't say anything about vias and other potential problems.
>
> At first pass, it seems that a trace size to handle twice the power cord's
max
> current, (from the nomograph) with a 10degC trace temperature rise (from
the PC
> trace chart), would be a good rule of thumb for the trace size.  If I have
room,
> I'll just make it bigger.  Once we pay for the PC board fabrication, the
copper
> is free!
>
> Even with an  adequately sized trace; I can think of a few potential
problems
> with the trace to chassis connection:
>
> 1.  Many layout people open up PC traces or planes around vias so that
only four
> little 20 mil wide bridges carry the current to the via.  This is great
for
> soldering heat relief; but BAD for current carrying capacity.  These
little
> bridges can fuse open in high current conditions.  I am con

RE: EN60950 protective conductor test (was Re: Circuit Breaker Tripping Dring Fault Tests)

[cnew...@xycom.com]

A slight divergence from the EN specifically, but I thought that the
following would be helpful to this thread:

I am presently working this issue with a UL engineer in accordance with
UL 60950, 3rd Edition.   I also have the UL 60950 3rd Ed. Test Data Sheets.
Their "Protective Earthing Trace Earth Fault Current Test", UL Doc. 190.eng,
per Section 2.6.3.3 requires the following in my case:

1.  Three samples are tested;

2.  Trace resistance is measured before and after test.  Resistance cannot
  exceed 0.1 ohms, and cannot change more than 10% after test;

3.  AC source is 240 Vac, 200 amps (20A circuit breaker X 10), power factor
  is 75 - 80% through shorted bus bars with a 20/30 A (20 in my case)
service
  entrance type circuit breaker in series with the testing terminals.  The
circuit
  breaker is connected to the bus bars by 1.22 m (4 ft.) of #12 AWG wire.

4.  The test circuit is connected to the DUT via the grounding lead of the
  1.82 m (6 ft) power supply cord.  If cord is not provided, then #16 AWG
  wire is used.

5.  Test continues until ultimate results occur; e.g. CB trips, trace opens,
etc.

My UL guy tells me that I should expect the typical service type CB to be rated
up to  + 10%.  So it appears that  I need to concern myself with a burst of
current
up to approximately 22 amps for the 20 amp AC circuit that my product is being
evaluated for.

Carl





From: "Chris Maxwell"  on 02/03/2003 09:29 AM

Please respond to "Chris Maxwell" 

To:   emc-p...@majordomo.ieee.org
cc:(bcc: Carl Newton/XYCOM)

Subject:  RE: EN60950 protective conductor test (was Re: Circuit Breaker
  Tripping Dring Fault Tests)




This thread has been interesting.  I am, at this moment, considering a design
where I am almost forced to use a PC (printed circuit) trace for Earth ground.

It seems funny to me that most equipment has been historically made with 18AWG
protective ground pigtail wires; and 25A ground fault tests have been used for
years.

Now that PC  traces are being used for protective ground; we want to test with
200A or greater impulse currents?  I'm curious about what would happen to your
typical 18AWG line cord during this test.  I'm wondering if the line cord would
fuse open?

There are a couple of handy charts on the web.

One is at www.kepcopower.com/nomovax2.htm this is a nomograph of maximum
operating current, AWG and IR drop in the conductor.  The point "A" is
generally
considered the point of maximum IR drop.  If you draw a line from point "A",
through a wire gauge size; you'll get a max current.  Of course this is steady
state current; and the nomograph assumes a single wire.  Wire bundles would be
a
worse case.  It's too bad that this chart doesn't contain the "fuse" values for
the wires as well (the  I squared * T values).

Another is at www.circuitboards.com/capacity.php3.   This is a chart of max
current for PC traces.  Remember that this is for TRACES and planes only; it
doesn't say anything about vias and other potential problems.

At first pass, it seems that a trace size to handle twice the power cord's max
current, (from the nomograph) with a 10degC trace temperature rise (from the PC
trace chart), would be a good rule of thumb for the trace size.  If I have
room,
I'll just make it bigger.  Once we pay for the PC board fabrication, the copper
is free!

Even with an  adequately sized trace; I can think of a few potential problems
with the trace to chassis connection:

1.  Many layout people open up PC traces or planes around vias so that only
four
little 20 mil wide bridges carry the current to the via.  This is great for
soldering heat relief; but BAD for current carrying capacity.  These little
bridges can fuse open in high current conditions.  I am considering solving
this
by not putting any thermal reliefs around your Earth ground vias and using
multiple vias.

2.  Another problem with these traces is using plated through vias with screws
through them.It has been found that plated through vias can crack when they
are put under pressure from screws.Some power supply manufacturers solve
this by bringing the Earth ground trace to the surface with vias near the
chassis connection point; then route this to a solid plated pad on the surface
layer for chassis connection.  I am considering this same solution as well.

3.  The third problem is mechanical.  Once Earth ground brought to a pad on the
circuitboard; then there is still the issue of getting a good mechanical mate
to
the chassis with a wide surface area.  If the connection is made through a
couple of teeth on a star washer; then there is a potential for localized
heating.   I'm just going to maximize surface contact area for this one.  I'm
also considering using multiple board to chassis connection locations.  Every
screw that connects the board to chassis is a potential Earth

RE: EN60950 protective conductor test (was Re: Circuit Breaker Tripping Dring Fault Tests)

[Chris Maxwell]

This thread has been interesting.  I am, at this moment, considering a design
where I am almost forced to use a PC (printed circuit) trace for Earth ground.

It seems funny to me that most equipment has been historically made with 18AWG
protective ground pigtail wires; and 25A ground fault tests have been used for
years.  

Now that PC  traces are being used for protective ground; we want to test with
200A or greater impulse currents?  I'm curious about what would happen to your
typical 18AWG line cord during this test.  I'm wondering if the line cord
would fuse open? 

There are a couple of handy charts on the web.

One is at www.kepcopower.com/nomovax2.htm this is a nomograph of maximum
operating current, AWG and IR drop in the conductor.  The point "A" is
generally considered the point of maximum IR drop.  If you draw a line from
point "A", through a wire gauge size; you'll get a max current.  Of course
this is steady state current; and the nomograph assumes a single wire.  Wire
bundles would be a worse case.  It's too bad that this chart doesn't contain
the "fuse" values for the wires as well (the  I squared * T values).

Another is at www.circuitboards.com/capacity.php3.   This is a chart of max
current for PC traces.  Remember that this is for TRACES and planes only; it
doesn't say anything about vias and other potential problems.  

At first pass, it seems that a trace size to handle twice the power cord's max
current, (from the nomograph) with a 10degC trace temperature rise (from the
PC trace chart), would be a good rule of thumb for the trace size.  If I have
room, I'll just make it bigger.  Once we pay for the PC board fabrication, the
copper is free!

Even with an  adequately sized trace; I can think of a few potential problems
with the trace to chassis connection:

1.  Many layout people open up PC traces or planes around vias so that only
four little 20 mil wide bridges carry the current to the via.  This is great
for soldering heat relief; but BAD for current carrying capacity.  These
little bridges can fuse open in high current conditions.  I am considering
solving this by not putting any thermal reliefs around your Earth ground vias
and using multiple vias.

2.  Another problem with these traces is using plated through vias with screws
through them.It has been found that plated through vias can crack when
they are put under pressure from screws.Some power supply manufacturers
solve this by bringing the Earth ground trace to the surface with vias near
the chassis connection point; then route this to a solid plated pad on the
surface layer for chassis connection.  I am considering this same solution as
well.

3.  The third problem is mechanical.  Once Earth ground brought to a pad on
the circuitboard; then there is still the issue of getting a good mechanical
mate to the chassis with a wide surface area.  If the connection is made
through a couple of teeth on a star washer; then there is a potential for
localized heating.   I'm just going to maximize surface contact area for this
one.  I'm also considering using multiple board to chassis connection
locations.  Every screw that connects the board to chassis is a potential
Earth ground connection.

The last "fuse" in any power system is the cord connected to the product.  It
seems to me, (just an opinion now) that a Earth ground system made to handle
the worst case current of your worst case power input cable (along with some
design margin) would stand a good chance of passing any regulatory test.  

Can any of the gurus see a problem with this?

Chris Maxwell | Design Engineer - Optical Division
email chris.maxw...@nettest.com | dir +1 315 266 5128 | fax +1 315 797 8024

NetTest | 6 Rhoads Drive, Utica, NY 13502 | USA
web www.nettest.com | tel +1 315 797 4449 | 







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Re: EN60950 protective conductor test (was Re: Circuit Breaker Tripping Dring Fault Tests)

[John Woodgate]

I read in !emc-pstc that Nick Williams 
wrote (in ) about 'EN60950
protective conductor test (was Re: Circuit Breaker Tripping Dring Fault
Tests)' on Fri, 31 Jan 2003:
>
>At 12:22 + 31/1/03, John Woodgate wrote:
>>
>>There is a proposed amendment to IEC/EN 60950-1 requiring a test of the
>>protective conductor network at *prospective short-circuit current* for
>>the time it takes for the mains circuit protective device to operate.
>>The details are controversial at present, because the test currents
>>appear not to have taken into account the differences between
>>prospective short-circuit currents in different wiring systems and
>>supply voltages. Given that reservation, the lowest test current is 200
>>A.
>>
>>The amendment is aimed at protective conductors which are surface or
>>internal traces of multi-layer printed boards. It is said that such
>>traces have failed in the field under high-current fault conditions.
>>--
>
>Is the proposal to replace the existing test in the standard or to 
>add an additional  test only for certain special circumstances?

It's additional.
>
>Is there any evidence that this test would actually result in a 
>significant number of poorly designed products which currently pass 
>the requirements of the standard being rejected?

This is the claimed justification for the introduction. Field problems
have occurred where printed board conductors have failed in high-current
short-circuit conditions. The printed-board mounting versions of the IEC
60320 appliance connector encourage the use of board traces to carry the
PEC; something that I would not be happy about, in principle. 
>
>The existing test has its faults but it is easy to do with some very 
>cheap apparatus. It strikes me that the cost of doing a test at 200+A 
>is potentially very substantial. 

I don't think 200 A is too much of a problem, but testing at higher
currents is proposed for some equipment. I don't want to be too
explicit, because the figures in the draft are highly suspect (of
applying to 120 V supplies!).

>If the result of an amendment to the 
>standard is that significant numbers of self-certified products which 
>have not been properly tested in this aspect of their design reach 
>the market, then the net result will actually be a significant 
>reduction in the safety of end users.

I don't understand that. You mean that if people cheat, safety will be
compromised? That's always the case. But in fact, the presence of the
test may well concentrate attention on the need to make such traces
substantial, whether they are tested or not.
>
>A cynic's view might also be that an amendment of this nature would 
>suit the test labs and larger manufacturers fine, since they will be 
>able to justify the cost of the apparatus required, whereas smaller 
>manufacturers (and yes, small consultancy companies like mine) will 
>not.
Remember you don't necessarily need 200 A at 230 V. I can get 200 A at a
bit over 1 V from a single turn on a big toroidal transformer.
>
>OK, I admit I'm putting two and two together and getting about seven 
>but I believe one should get one's retaliation in first in these 
>circumstances! Any amendment along the lines suggested should be 
>prepared to sacrifice a fair degree of technical accuracy against the 
>need for the test to be cheap, quick and easy to perform.

It doesn't call for technical accuracy. You zap the equipment with the
200 A current for the operating time of the protective device and the
PEC either remains intact or doesn't.
>
>Nowadays, standards writing should not just about getting accuracy 
>and repeatability in testing but should also take into account the 
>need to ensure that the requirements (and hence the tests) are 
>actually possible to apply in the real world, and not just by people 
>at specialist test houses.
>
I quite agree, but as you indicate above, there isn't too much *active*
support for that view. When I talk in the committees about low-cost
testing, people tend to remain silent. In any case, at present it's
difficult enough coping with the problems of the costly test equipment
not measuring correctly or not being feasible (low-distortion, high-
current mains supplies for IEC 61000-3-12, as a case in point).

If you want a copy of the draft, to make comments to the BSI committee,
please e-mail. Note that this offer can only be made to people in UK.
Others should approach their national standards body.
-- 
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk 
Interested in professional sound reinforcement and distribution? Then go to 
http://www.isce.org.uk
PLEASE do NOT copy news posts to me by E-MAIL!


This message is from the IEEE EMC Society Pro

RE: Circuit Breaker Tripping Dring Fault Tests

[Jim Eichner]

The approach that CSA takes is sensible in that it includes both the long
duration overload and high-current short circuit capabilities of the source.
Depending on your situation you can end up needing to do one or both of the
following:

1. Bond Impedance - run a current equal to 200% of the branch circuit
breaker rating through the bonding path for 2 minutes (derived from the I
vs. t curves allowed by CSA breaker standards).

2. Bond Limited short-circuit withstand - done at up to 5000A depending on
the supply circuit the product will be connected to; this test is performed
only when the capacity of the bonding path is in doubt (e.g. pcb traces).

Jim Eichner, P.Eng. 
Regulatory Compliance Manager  
Xantrex Technology Inc. 
e-mail: jim.eich...@xantrex.com 
web: www.xantrex.com 

Any opinions expressed are those of my invisible friend, who really exists.
Honest.  No really.

Confidentiality Notice: This email message, including any attachments, is
for the sole use of the intended recipient(s) and may contain confidential
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contact the sender by reply e-mail and destroy all copies of the original
message.



From: Peter L. Tarver [mailto:peter.tar...@sanmina-sci.com]
Sent: Friday, January 31, 2003 9:23 AM
To: John Woodgate; emc-p...@majordomo.ieee.org
Subject: RE: Circuit Breaker Tripping Dring Fault Tests



John -

This proposal is based on a North American D1 Deviation to
IEC60950, Subclause 2.6.3.3, and is derived from CSA 22.2 No
0.4.  I have a product in my lab that this applies to and
two more products coming in to which it will also apply.


Regards,

Peter L. Tarver, PE
Product Safety Manager
Sanmina-SCI Homologation Services
San Jose, CA
peter.tar...@sanmina-sci.com

> From: John Woodgate
>
> There is a proposed amendment to IEC/EN 60950-1
> requiring a test of the
> protective conductor network at *prospective
> short-circuit current* for
> the time it takes for the mains circuit
> protective device to operate.
> The details are controversial at present, because
> the test currents
> appear not to have taken into account the
> differences between
> prospective short-circuit currents in different
> wiring systems and
> supply voltages. Given that reservation, the
> lowest test current is 200
> A.
>
> The amendment is aimed at protective conductors
> which are surface or
> internal traces of multi-layer printed boards. It
> is said that such
> traces have failed in the field under
> high-current fault conditions.



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EN60950 protective conductor test (was Re: Circuit Breaker Tripping Dring Fault Tests)

[Nick Williams]

At 12:22 + 31/1/03, John Woodgate wrote:
>
>There is a proposed amendment to IEC/EN 60950-1 requiring a test of the
>protective conductor network at *prospective short-circuit current* for
>the time it takes for the mains circuit protective device to operate.
>The details are controversial at present, because the test currents
>appear not to have taken into account the differences between
>prospective short-circuit currents in different wiring systems and
>supply voltages. Given that reservation, the lowest test current is 200
>A.
>
>The amendment is aimed at protective conductors which are surface or
>internal traces of multi-layer printed boards. It is said that such
>traces have failed in the field under high-current fault conditions.
>--

Is the proposal to replace the existing test in the standard or to 
add an additional  test only for certain special circumstances?

Is there any evidence that this test would actually result in a 
significant number of poorly designed products which currently pass 
the requirements of the standard being rejected?

The existing test has its faults but it is easy to do with some very 
cheap apparatus. It strikes me that the cost of doing a test at 200+A 
is potentially very substantial. If the result of an amendment to the 
standard is that significant numbers of self-certified products which 
have not been properly tested in this aspect of their design reach 
the market, then the net result will actually be a significant 
reduction in the safety of end users.

A cynic's view might also be that an amendment of this nature would 
suit the test labs and larger manufacturers fine, since they will be 
able to justify the cost of the apparatus required, whereas smaller 
manufacturers (and yes, small consultancy companies like mine) will 
not.

OK, I admit I'm putting two and two together and getting about seven 
but I believe one should get one's retaliation in first in these 
circumstances! Any amendment along the lines suggested should be 
prepared to sacrifice a fair degree of technical accuracy against the 
need for the test to be cheap, quick and easy to perform.

Nowadays, standards writing should not just about getting accuracy 
and repeatability in testing but should also take into account the 
need to ensure that the requirements (and hence the tests) are 
actually possible to apply in the real world, and not just by people 
at specialist test houses.

Regards

Nick.


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RE: Circuit Breaker Tripping Dring Fault Tests

[Peter L. Tarver]

John -

This proposal is based on a North American D1 Deviation to
IEC60950, Subclause 2.6.3.3, and is derived from CSA 22.2 No
0.4.  I have a product in my lab that this applies to and
two more products coming in to which it will also apply.


Regards,

Peter L. Tarver, PE
Product Safety Manager
Sanmina-SCI Homologation Services
San Jose, CA
peter.tar...@sanmina-sci.com

> From: John Woodgate
>
> There is a proposed amendment to IEC/EN 60950-1
> requiring a test of the
> protective conductor network at *prospective
> short-circuit current* for
> the time it takes for the mains circuit
> protective device to operate.
> The details are controversial at present, because
> the test currents
> appear not to have taken into account the
> differences between
> prospective short-circuit currents in different
> wiring systems and
> supply voltages. Given that reservation, the
> lowest test current is 200
> A.
>
> The amendment is aimed at protective conductors
> which are surface or
> internal traces of multi-layer printed boards. It
> is said that such
> traces have failed in the field under
> high-current fault conditions.



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Re: Circuit Breaker Tripping Dring Fault Tests

[John Woodgate]

I read in !emc-pstc that Peter L. Tarver 
wrote (in )
about 'Circuit Breaker Tripping Dring Fault Tests' on Thu, 30 Jan 2003:
>
>John -
>
>That impedance value is suprisingly high, 


It applies to 230 V 50 Hz systems only. SC77A/WG2 has been given a too
limited amount of data on 120 V 60 Hz systems to deduce a reference
value, but it seems to be rather less than half the 230 V value, because
permitted voltage tolerances in 120 V systems tend to be +/-5%, less
than in Europe (6 to 10%).

>but tends to
>support the contention that the fault current at an outlet
>will be much lower than was suggested (65kA, which, to me,
>appeared more like a peak surge current than a fault
>current).

Yes, 65 kA is way too high.
>
>For those interested, below are what the IEC Web Store has
>to say about IEC 60725.
>
>Title: Considerations on reference impedances for use in
>determining the disturbance characteristics of household
>appliances and similar electrical equipment
>
>Abstract: Records the information that was available and the
>factors that were taken into account in arriving at the
>reference impedance of 0.4+ j 0.25 ohm which has been
>incorporated in IEC 60555. Has the status of a technical
>report.

A revision is under way. Postpone your buying decision.(;-)

It doesn't alter the reference impedance but adds information of
calculating the impedances of (particularly) higher-current services,
applicable to any system voltage and permitted voltage variation.
>
>0.5 Ohm seems large for a flexible cord.
>
0.5 ohms is 0.2 ohm total for the two conductors of the flexible plus
0.3 ohm total for the two conductors of the feed to the wall socket. All
in a 230 V system. It's just an example. 
-- 
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk 
Interested in professional sound reinforcement and distribution? Then go to 
http://www.isce.org.uk
PLEASE do NOT copy news posts to me by E-MAIL!


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Re: Circuit Breaker Tripping Dring Fault Tests

[John Woodgate]

I read in !emc-pstc that John Woodgate  wrote (in
) about 'Circuit Breaker Tripping
Dring Fault Tests' on Wed, 29 Jan 2003:
>I read in !emc-pstc that Peter L. Tarver 
>wrote (in )
>about 'Circuit Breaker Tripping Dring Fault Tests' on Wed, 29 Jan 2003:
>>In a typical household operating at 120V, it's unlikely
>>that a fault current available to Pluggable Equipment Type A
>>will be much above 5kA, even if the outlet supplying the
>>equipment is within 5 ft. of the service entrance.  In a
>>typical household operating at 240V, the available fault
>>current will be somewhat higher (approximately doubled +).
>
>H'mm. IEC 60725 gives a 'reference impedance' (a sort of weighted
>average, omitting extreme values) for a 230 V 50 Hz 100 A service-rating
>household supply as 0.47 ohms at the service entry.   Allowing another
>0.5 ohms for the mains wiring and the flexible mains lead, we get 230 V
>and 0.97 ohms at the appliance, giving a prospective short-circuit
>current of about 240 A. The appliance fuse should be able to interrupt
>that without exploding.
>
>UK plug-top fuses are tested to break 6000 A safely, though.

There is a proposed amendment to IEC/EN 60950-1 requiring a test of the
protective conductor network at *prospective short-circuit current* for
the time it takes for the mains circuit protective device to operate.
The details are controversial at present, because the test currents
appear not to have taken into account the differences between
prospective short-circuit currents in different wiring systems and
supply voltages. Given that reservation, the lowest test current is 200
A. 

The amendment is aimed at protective conductors which are surface or
internal traces of multi-layer printed boards. It is said that such
traces have failed in the field under high-current fault conditions.
-- 
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk 
Interested in professional sound reinforcement and distribution? Then go to 
http://www.isce.org.uk
PLEASE do NOT copy news posts to me by E-MAIL!


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RE: Circuit Breaker Tripping Dring Fault Tests

[Peter L. Tarver]

John -

That impedance value is suprisingly high, but tends to
support the contention that the fault current at an outlet
will be much lower than was suggested (65kA, which, to me,
appeared more like a peak surge current than a fault
current).

For those interested, below are what the IEC Web Store has
to say about IEC 60725.

Title: Considerations on reference impedances for use in
determining the disturbance characteristics of household
appliances and similar electrical equipment

Abstract: Records the information that was available and the
factors that were taken into account in arriving at the
reference impedance of 0.4+ j 0.25 ohm which has been
incorporated in IEC 60555. Has the status of a technical
report.

0.5 Ohm seems large for a flexible cord.


Regards,

Peter L. Tarver, PE
Product Safety Manager
Sanmina-SCI Homologation Services
San Jose, CA
peter.tar...@sanmina-sci.com

> -Original Message-
> From: John Woodgate
> Sent: Wednesday, January 29, 2003 2:10 PM
>
>
> H'mm. IEC 60725 gives a 'reference impedance' (a
> sort of weighted
> average, omitting extreme values) for a 230 V 50
> Hz 100 A service-rating
> household supply as 0.47 ohms at the service
> entry.   Allowing another
> 0.5 ohms for the mains wiring and the flexible
> mains lead, we get 230 V
> and 0.97 ohms at the appliance, giving a
> prospective short-circuit
> current of about 240 A.



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Re: Circuit Breaker Tripping Dring Fault Tests

[John Woodgate]

I read in !emc-pstc that Peter L. Tarver 
wrote (in )
about 'Circuit Breaker Tripping Dring Fault Tests' on Wed, 29 Jan 2003:
>In a typical household operating at 120V, it's unlikely
>that a fault current available to Pluggable Equipment Type A
>will be much above 5kA, even if the outlet supplying the
>equipment is within 5 ft. of the service entrance.  In a
>typical household operating at 240V, the available fault
>current will be somewhat higher (approximately doubled +).

H'mm. IEC 60725 gives a 'reference impedance' (a sort of weighted
average, omitting extreme values) for a 230 V 50 Hz 100 A service-rating
household supply as 0.47 ohms at the service entry.   Allowing another
0.5 ohms for the mains wiring and the flexible mains lead, we get 230 V
and 0.97 ohms at the appliance, giving a prospective short-circuit
current of about 240 A. The appliance fuse should be able to interrupt
that without exploding.

UK plug-top fuses are tested to break 6000 A safely, though.
-- 
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk 
Interested in professional sound reinforcement and distribution? Then go to 
http://www.isce.org.uk
PLEASE do NOT copy news posts to me by E-MAIL!


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RE: Circuit Breaker Tripping Dring Fault Tests

[Peter L. Tarver]

From: Gregg Kervill
Sent: Tuesday, January 28, 2003 3:21 PM

> Like most regulatory issues the answer is YES and NO.
>
> Therefore it is dangerous and extremely misleading (to
many
> lurkers) to apply a general answer to all conditions:
>
> Generally the equipment is expected to protect itself with
> internal over current and short-circuit protection.

I disagree.  It may be possible for equipment to possess
inherent features that do not require supplementary
protection or that a piece of equipment is adequately
protected by the branch circuit protection.  Much depends on
the application and design.

> The equipment will be tested with the worst case fault
> condition – 60 kAmp or more is not uncommon

This value may be true for equipment installed in Category
IV and possibly Category III environments (per IEC60664-1),
but is neither the general case nor very common for
equipment installed in Category II environments.  Consider
that every finite (though minute) impedance at every
electrical connection will serve to limit the fault current
available at equipment.  Impedances will also exist at each
switchable contact (molded case switches and circuit
breakers) and each wiping contact (fuse holders for
replaceable cartridge fuses, outlets/plugs, knife switches).

For North America:

In a typical household operating at 120V, it's unlikely
that a fault current available to Pluggable Equipment Type A
will be much above 5kA, even if the outlet supplying the
equipment is within 5 ft. of the service entrance.  In a
typical household operating at 240V, the available fault
current will be somewhat higher (approximately doubled +).
This is also, in large measure, due to the relatively small
last distribution transformer before the household and other
loads on the transformer from other households supplied by
the same transformer.

In a typical business the fault current available will be
larger, due largely to a larger transformer connected to the
service entrance and that the service entrance voltages are
greater (480V three phase is not uncommon for larger
facilities; 120/208V is most common).  I'm not certain of
the typical fault currents available at an outlet in this
case, but I'd venture a guess that its not more than 25kA at
a ANSI/NEMA 5-15 outlet.

I'm interested in hearing typical values for other regions
of the world, so if anyone has any data or reasonable
guesses, please let us all know.

> Where we rely upon the ‘breaker’ for - non-domestic
> equipment - it is ALWAYS mandatory (and common sense)
> to specify the characteristics of that breaker in
> terms of  ‘tripping (operating) current’ – time
> characteristics (Type I, II or III) and Breaking
> Current 2,500 Amps is low for most domestic situations.

This must be for Europe.  In the US (and I believe Canada is
the same), 5kA is a gimme interrupting rating for molded
case switches and circuit breakers.  The minimum
interrupting rating for branch circuit fuses is 10kA.

> A failure to provide the necessary information
> WILL eventually result in a fire or nuisance tripping.

Or not, depending on the installation environment.

> Best regards

> Gregg


Regards,

Peter L. Tarver, PE
Product Safety Manager
Sanmina-SCI Homologation Services
San Jose, CA
peter.tar...@sanmina-sci.com



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RE: Circuit Breaker Tripping Dring Fault Tests

[Peter L. Tarver]

Richard -

The requirement applied below is due to the largest
commercially available fuse size for a form factor.  The
smallest branch circuit protection fuse form factors (both
Edison base and cartridge) serve up to 30A.  Interesting
that they'd require a time-delay fuse, but that must be
because you can fit a time-delay fuse into a nontime-delay
fuse holder.

I'm more surprised that an Edison base was required, rather
than allowing a cartridge type.  Was there a particular
rationale for this?


Regards,

Peter L. Tarver, PE
Product Safety Manager
Sanmina-SCI Homologation Services
San Jose, CA
peter.tar...@sanmina-sci.com


From: Richard Pittenger
Sent: Wednesday, January 29, 2003 4:58 AM


Rich and group,

Just one interesting point continuing the thought of
fuse sizes for branch circuit protection. Awhile back, I was
conducting a series of UL tests on a household food mixer.
For one of the abnormal tests, UL required me to use a 30 A
time-delay branch circuit fuse (lamp base) in the power
supply to the unit under test. I thought this was extreme,
believing that a 20  A fuse would be the maximum anyone
would ever use. When questioned, I was told that such fuses
are available and still in use, primarily in old residential
areas.

I visited my local hardware store and, sure enough,
they were readily available, right along with the other more
common sizes. You may want to consider this when considering
such tests in the future.

Good day,

Richard Pittenger
Agency Approval Engineer
Hobart Corporation



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RE: Circuit Breaker Tripping Dring Fault Tests

[gkt4s]

Thank you Richard – this situation vividly illustrates the danger of
nuisances tripping – what message does that give to the Home Owner –
“FIT A BIGGER FUSE!”
 
That is why (some) CSA standards require a Turn-On Test – ON-OFF 10 times
within a minute – protection devices MUST NOT OPERATE.
 
I have been recommending this test to clients as GOOD ENGINEERING PRACTICE for
the last 10 years.
 
Best regards
 
Gregg
 
 

From: owner-emc-p...@majordomo.ieee.org
[mailto:owner-emc-p...@majordomo.ieee.org]On Behalf Of
richard.pitten...@hobartcorp.com
Sent: Wednesday, January 29, 2003 7:58 AM
To: Rich Nute
Cc: emc-p...@majordomo.ieee.org
Subject: Re: Circuit Breaker Tripping Dring Fault Tests
 

Rich and group, 

Just one interesting point continuing the thought of fuse sizes for
branch circuit protection. Awhile back, I was conducting a series of UL tests
on a household food mixer. For one of the abnormal tests, UL required me to
use a 30 A time-delay branch circuit fuse (lamp base) in the power supply to
the unit under test. I thought this was extreme, believing that a 20  A fuse
would be the maximum anyone would ever use. When questioned, I was told that
such fuses are available and still in use, primarily in old residential areas. 
I visited my local hardware store and, sure enough, they were readily
available, right along with the other more common sizes. You may want to
consider this when considering such tests in the future. 

Good day, 

Richard Pittenger
Agency Approval Engineer
Hobart Corporation




 
Rich Nute  
Sent by: owner-emc-p...@majordomo.ieee.org 
01/28/2003 07:23 PM 
Please respond to Rich Nute 

To:pmerguerian2...@yahoo.com 
cc:emc-p...@majordomo.ieee.org 
Subject:Re: Circuit Breaker Tripping Dring Fault Tests







Hi Peter:


>   For safety, it is not clear from the standards whether 
>   the main branch circuit breaker tripping during fault 
>   conditions is an acceptable result.
>   
>   I see no reason why this should not be acceptable. What 
>   is your view? Some third party labs find it acceptable 
>   and others do not.

Some products are provided with internal overcurrent
protection and some are not.  

Clearly, those that do not have internal overcurrent
protection rely on the branch circuit protection.

If a product has an internal overcurrent protective
device, and the fault is on the load side of that 
device, then the internal device should provide the
protection and not the branch circuit device.  
(Otherwise, the internal device provides no 
protection, and might as well be removed.)

If the fault is on the supply side of the internal
device, then clearly the internal device cannot 
provide protection, and the branch circuit must 
provide the protection.  

The real question is whether or not the product is
safe when the fault current is just below the
operating point of the branch circuit device.  
Examining this question requires an understanding
of the fault and whether its resistance can be high
enough to not trip the branch circuit yet not create
a hazardous condition (such as a fire).  If the 
fault resistance always is no more than 120/20 = 6 
ohms, then I would say that the branch circuit 
could be relied upon to provide protection against
the fault.

Note that in the USA, a 120-volt branch circuit can
be provided with either a 15-amp or a 20-amp
overcurrent device.  Therefore, the product must be
safe when the fault current is 20 amps, just below
the overcurrent device operating point.  That means
that the product must be capable of dissipating 
2400 watts without catching fire or destroying 
internal insulation that serves a safety purpose.


Best regards,
Rich






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RE: Circuit Breaker Tripping Dring Fault Tests

[Peter L. Tarver]

Peter -

I agree that this is an acceptable result in the US and
Canada.  There are, however, additional considerations:

For Pluggable Equipment Type A (to borrow a term from the
60950 standards), the largest branch circuit protection is
assumed during testing (20A) and there is no further
requirement.

For Pluggable Equipment Type B and permanently connected
equipment, it would then be necessary to specify the largest
branch circuit protection device the equipment may be safely
supplied from in the installation instructions.  This would
necessarily be the size of the protection involved during
your testing.

I am very interested in the nonNorth American view on this
issue.


Regards,

Peter L. Tarver, PE
Product Safety Manager
Sanmina-SCI Homologation Services
San Jose, CA
peter.tar...@sanmina-sci.com



From: peter merguerian
Sent: Tuesday, January 28, 2003 11:54 AM

Dear All,
For safety, it is not clear from the standards whether the
main branch circuit breaker tripping during fault conditions
is an acceptable result.

I see no reason why this should not be acceptable. What is
your view? Some third party labs find it acceptable and
others do not.

Anyone can lead me to some inernational decisions regarding
this issue?

Thanks,
Peter




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RE: Circuit Breaker Tripping Dring Fault Tests

[Garnier, David S (MED)]

I am going to jump into this frey, here is my 2 cents...
 
In the case of Medical Electronics, if the fault condition would cause 
more exposure of radiation to the patient than what was "dialed in"
(X-Ray, MRI, Ultrasound) that would be a BAD thing. End of subject.
 
dave garnier


From: Lou Aiken [mailto:ai...@gulftel.com]
Sent: Tuesday, January 28, 2003 11:00 PM
To: peter merguerian; emc-p...@majordomo.ieee.org
Subject: Re: Circuit Breaker Tripping Dring Fault Tests


Here is what I think the requirements are:
 
If the product remains safe, within the meaning of the standard, and the
branch circuit overcurrent protection device does, or does not, operate as a
result of fault testing, internal overcurrent is unnecessary.
 
If the product does NOT remain safe, within the meaning of the standard, as a
result of fault testing, internal overcurrent protection IS necessary, branch
circuit overcurrent protection is   inadequate, and internal overcurrent
protection is necessary.
 
Safe within the meaning of the standard:  Does not exceed allowable fault
temperature limits, does not catch fire, enclosure does not deform to the
extent that parts involving the risk of electric shock or personal injury
become exposed to the test finger or probe, will pass the required electric
strength test after the fault, etc.
 
IN order to be confident that the design is safe one must continue the fault
testing until steady state conditions exist, OR for the maximum clearing time
(for the resulting fault current) as stated in the standard for the particular
overcurrent device.  It is incorrect consider the result acceptable when the
overcurrent device opens the circuit.  The overcurrent device should be
removed from the circuit and the current monitored during the fault test. 
Only approved fuses and circuit breakers should be specified if they are
necessary make the product remain safe - within the meaning of the standard.
 
There is a significant difference in the endurance and clearing limits between
the UL and IEC standards for fuses and circuit breakers with the same current
rating. 
 
 
 
Lou Aiken, LaMer LLC 
27109 Palmetto Drive
Orange Beach, AL
36561 USA
 
tel ++ 1 251 981 6786
fax ++ 1 251 981 3054
Cell ++ 1 251 979 4648

- Original Message - 
From: peter merguerian <mailto:pmerguerian2...@yahoo.com>  
To: emc-p...@majordomo.ieee.org 
Sent: Tuesday, January 28, 2003 1:54 PM
Subject: Circuit Breaker Tripping Dring Fault Tests


Dear All,

For safety, it is not clear from the standards whether the main branch circuit
breaker tripping during fault conditions is an acceptable result.

I see no reason why this should not be acceptable. What is your view? Some
third party labs find it acceptable and others do not.

Anyone can lead me to some inernational decisions regarding this issue?

Thanks,

Peter

 

 




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RE: Circuit Breaker Tripping Dring Fault Tests

[Robert Johnson]

 
Two points:

To assure the safety of your product consider not whether it is safe if the
breaker trips, but what is the failure mode of your product if the breaker
(which you do not provide) does not trip. If you rely on the breaker, you
need to properly specify it.

In the US, there have been code changes to introduce a new device called an
arc fault interrupting breaker which uses RF noise from an arc to trip a
breaker at currents below normal overcurrent trip levels. This was
introduced because there were many instances where an arc in power cords or
similar places would generate enough energy to melt copper and blast it
away. The molten copper is capable of starting fires. Often the breaker
failed to trip during this momentary fault, and permitted arc tracking to
cause repeated cycles of arcs. The message is, some types of failures are
not well protected by ordinary overcurrent devices. This may or may not be
relevant in your case.


Bob Johnson
ITE Safety



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RE: Circuit Breaker Tripping Dring Fault Tests

[Kurt Mikolajewski]

Jim
 
I your case the required BASIC INSULATION is not present or adequate. BASIC
INSULATION provides a level of protection. The branch circuit provides an
additional level of protection if there is a failure of the BASIC INSULATION.
The standard in this instance allows the designer to provide an alternate
protection method to replace the BASIC INSULATION, with the requirement that
it fails safe and it does not impact any other insulation system. 
 
Regards,
Kurt Mikolajewski


From: Jim Eichner [mailto:jim.eich...@xantrex.com]
Sent: Tuesday, January 28, 2003 5:13 PM
To: emc-p...@majordomo.ieee.org
Subject: RE: Circuit Breaker Tripping Dring Fault Tests


I've been trying to solve this one myself.  I work with one pair of standards
(UL458 / CSA107.1) where they specifically say that opening the branch circuit
protection is acceptable during component fault testing, but NOT during short
circuit tests done for the purposes of validating inadequate trace spacings
(an easement offered in the standards in some situations).  I've always been
puzzled why we can't rely on branch circuit protection for both situations,
but neither agency has been able to explain the difference to me.
 
Jim Eichner, P.Eng.
Regulatory Compliance Manager
Xantrex Technology Inc.
phone: (604) 422-2546
fax: (604) 420-1591
e-mail: jim.eich...@xantrex.com
web: www.xantrex.com 
Confidentiality Notice: This email message, including any attachments, is for
the sole use of the intended recipient(s) and may contain confidential and
privileged information. Any unauthorized review, use, disclosure or
distribution is prohibited. If you are not the intended recipient, please
contact the sender by reply e-mail and destroy all copies of the original
message.

 




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RE: Circuit Breaker Tripping Dring Fault Tests

[bryan.c...@control-concepts.com]

Peter,
 
I do not have specifics, so I can only offer general information.
 
The use of external breakers is acceptable for testing and certifying products
that are hardwired to the electrical distribution of a facility for when fault
current or withstand testing is required.  In the US, the UL standards
typically denote the overall requirements of the test and pass/fail criteria. 
The NEC may also detail specific information about over-current protection for
specific devices.
 
When an external breaker is utilized, it is required to be denoted in the
installation instructions (UL requirement).  However, this does present some
issues when installed as the product may be preceded with a breaker that is
different than what was tested.  Remember, not all breakers are created equal.
 Therefore, testing of fault currents with one breaker may yield one result
and testing of another manufacturer's breaker may have a second result.
 
When products are cord connected, one is usually required to have internal
over-current protection.  However, I believe that this is a general guideline
not a stead fast rule.
 
Thanks,

Bryan Cole 
Director of Engineering 
Product Safety Officer 
Emerson Network Power - Control Concepts 
Binghamton, New York 13902 
Phone: 607.724.1352 extension 238 
Fax: 607.724.0153 
E-mail: bryan.c...@control-concepts.com 
www.Liebert.com 
www.Control-Concepts.com 
www.Edcosurge.com 


From: peter merguerian [mailto:pmerguerian2...@yahoo.com]
Sent: Tuesday, January 28, 2003 2:54 PM
To: emc-p...@majordomo.ieee.org
Subject: Circuit Breaker Tripping Dring Fault Tests



Dear All,

For safety, it is not clear from the standards whether the main branch circuit
breaker tripping during fault conditions is an acceptable result.

I see no reason why this should not be acceptable. What is your view? Some
third party labs find it acceptable and others do not.

Anyone can lead me to some inernational decisions regarding this issue?

Thanks,

Peter

 

 




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Re: Circuit Breaker Tripping Dring Fault Tests

[richard.pitten...@hobartcorp.com]

Rich and group, 

Just one interesting point continuing the thought of fuse sizes for
branch circuit protection. Awhile back, I was conducting a series of UL tests
on a household food mixer. For one of the abnormal tests, UL required me to
use a 30 A time-delay branch circuit fuse (lamp base) in the power supply to
the unit under test. I thought this was extreme, believing that a 20  A fuse
would be the maximum anyone would ever use. When questioned, I was told that
such fuses are available and still in use, primarily in old residential areas. 
I visited my local hardware store and, sure enough, they were readily
available, right along with the other more common sizes. You may want to
consider this when considering such tests in the future. 

Good day, 

Richard Pittenger
Agency Approval Engineer
Hobart Corporation




Rich Nute  
Sent by: owner-emc-p...@majordomo.ieee.org 


01/28/2003 07:23 PM 
Please respond to Rich Nute 

To:pmerguerian2...@yahoo.com 
cc:emc-p...@majordomo.ieee.org 
Subject:Re: Circuit Breaker Tripping Dring Fault Tests








Hi Peter:


>   For safety, it is not clear from the standards whether 
>   the main branch circuit breaker tripping during fault 
>   conditions is an acceptable result.
>   
>   I see no reason why this should not be acceptable. What 
>   is your view? Some third party labs find it acceptable 
>   and others do not.

Some products are provided with internal overcurrent
protection and some are not.  

Clearly, those that do not have internal overcurrent
protection rely on the branch circuit protection.

If a product has an internal overcurrent protective
device, and the fault is on the load side of that 
device, then the internal device should provide the
protection and not the branch circuit device.  
(Otherwise, the internal device provides no 
protection, and might as well be removed.)

If the fault is on the supply side of the internal
device, then clearly the internal device cannot 
provide protection, and the branch circuit must 
provide the protection.  

The real question is whether or not the product is
safe when the fault current is just below the
operating point of the branch circuit device.  
Examining this question requires an understanding
of the fault and whether its resistance can be high
enough to not trip the branch circuit yet not create
a hazardous condition (such as a fire).  If the 
fault resistance always is no more than 120/20 = 6 
ohms, then I would say that the branch circuit 
could be relied upon to provide protection against
the fault.

Note that in the USA, a 120-volt branch circuit can
be provided with either a 15-amp or a 20-amp
overcurrent device.  Therefore, the product must be
safe when the fault current is 20 amps, just below
the overcurrent device operating point.  That means
that the product must be capable of dissipating 
2400 watts without catching fire or destroying 
internal insulation that serves a safety purpose.


Best regards,
Rich






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Re: Circuit Breaker Tripping Dring Fault Tests

[Lou Aiken]

Here is what I think the requirements are:
 
If the product remains safe, within the meaning of the standard, and the
branch circuit overcurrent protection device does, or does not, operate as a
result of fault testing, internal overcurrent is unnecessary.
 
If the product does NOT remain safe, within the meaning of the standard, as a
result of fault testing, internal overcurrent protection IS necessary, branch
circuit overcurrent protection is   inadequate, and internal overcurrent
protection is necessary.
 
Safe within the meaning of the standard:  Does not exceed allowable fault
temperature limits, does not catch fire, enclosure does not deform to the
extent that parts involving the risk of electric shock or personal injury
become exposed to the test finger or probe, will pass the required electric
strength test after the fault, etc.
 
IN order to be confident that the design is safe one must continue the fault
testing until steady state conditions exist, OR for the maximum clearing time
(for the resulting fault current) as stated in the standard for the particular
overcurrent device.  It is incorrect consider the result acceptable when the
overcurrent device opens the circuit.  The overcurrent device should be
removed from the circuit and the current monitored during the fault test. 
Only approved fuses and circuit breakers should be specified if they are
necessary make the product remain safe - within the meaning of the standard.
 
There is a significant difference in the endurance and clearing limits between
the UL and IEC standards for fuses and circuit breakers with the same current
rating. 
 
 
 
Lou Aiken, LaMer LLC 
27109 Palmetto Drive
Orange Beach, AL
36561 USA
 
tel ++ 1 251 981 6786
fax ++ 1 251 981 3054
Cell ++ 1 251 979 4648

- Original Message - 
From: peter merguerian   
To: emc-p...@majordomo.ieee.org 
Sent: Tuesday, January 28, 2003 1:54 PM
Subject: Circuit Breaker Tripping Dring Fault Tests


Dear All,

For safety, it is not clear from the standards whether the main branch circuit
breaker tripping during fault conditions is an acceptable result.

I see no reason why this should not be acceptable. What is your view? Some
third party labs find it acceptable and others do not.

Anyone can lead me to some inernational decisions regarding this issue?

Thanks,

Peter

 

 




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Re: Circuit Breaker Tripping Dring Fault Tests

[Rich Nute]

Hi Peter:


>   For safety, it is not clear from the standards whether 
>   the main branch circuit breaker tripping during fault 
>   conditions is an acceptable result.
>   
>   I see no reason why this should not be acceptable. What 
>   is your view? Some third party labs find it acceptable 
>   and others do not.

Some products are provided with internal overcurrent
protection and some are not.  

Clearly, those that do not have internal overcurrent
protection rely on the branch circuit protection.

If a product has an internal overcurrent protective
device, and the fault is on the load side of that 
device, then the internal device should provide the
protection and not the branch circuit device.  
(Otherwise, the internal device provides no 
protection, and might as well be removed.)

If the fault is on the supply side of the internal
device, then clearly the internal device cannot 
provide protection, and the branch circuit must 
provide the protection.  

The real question is whether or not the product is
safe when the fault current is just below the
operating point of the branch circuit device.  
Examining this question requires an understanding
of the fault and whether its resistance can be high
enough to not trip the branch circuit yet not create
a hazardous condition (such as a fire).  If the 
fault resistance always is no more than 120/20 = 6 
ohms, then I would say that the branch circuit 
could be relied upon to provide protection against
the fault.

Note that in the USA, a 120-volt branch circuit can
be provided with either a 15-amp or a 20-amp
overcurrent device.  Therefore, the product must be
safe when the fault current is 20 amps, just below
the overcurrent device operating point.  That means
that the product must be capable of dissipating 
2400 watts without catching fire or destroying 
internal insulation that serves a safety purpose.


Best regards,
Rich






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Technical Committee emc-pstc discussion list.

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RE: Circuit Breaker Tripping Dring Fault Tests

[gkt4s]

Like most regulatory issues the answer is YES and NO.
 
Therefore it is dangerous and extremely misleading (to many lurkers) to apply
a general answer to all conditions:
 
*   Generally the equipment is expected to protect itself with internal over
current and short-circuit protection. 
 
*   The equipment will be tested with the worst case fault condition – 60 
kAmp
or more is not uncommon
 
*   If the equipment is simple and cannot be protect itself (e.g. a table 
lamp)
then we rely upon the domestic breaker (hoping that the electrician follow
CODE and not his own initiative) that is why the cord will have minimum
x-sectional area and maximum length. (Expect where UK style plugs are used -
these carry an internal fuse from 1 Amp to 13 Amps). It is also why CODE
violations are prosecuted – we must guarantee that the correct type of
breaker is fitted in each domestic circuit.
 
*   Where we rely upon the ‘breaker’ for - non-domestic equipment - it is
ALWAYS mandatory (and common sense) to specify the characteristics of that
breaker in terms of  ‘tripping (operating) current’ – time
characteristics (Type I, II or III) and Breaking Current 2,500 Amps is low for
most domestic situations.
 
A failure to provide the necessary information WILL eventually result in a
fire or nuisance tripping.
 
 
You should fine that all test labs will have the same interpretation – I
suspect that submissions PASSED are correct – whilst those that were
REJECTED were not correct.
 
Best regards
 
Gregg
 
 
 
 
 

From: owner-emc-p...@majordomo.ieee.org
[mailto:owner-emc-p...@majordomo.ieee.org]On Behalf Of peter merguerian
Sent: Tuesday, January 28, 2003 2:54 PM
To: emc-p...@majordomo.ieee.org
Subject: Circuit Breaker Tripping Dring Fault Tests
 
Dear All,
For safety, it is not clear from the standards whether the main branch circuit
breaker tripping during fault conditions is an acceptable result.
I see no reason why this should not be acceptable. What is your view? Some
third party labs find it acceptable and others do not.
Anyone can lead me to some inernational decisions regarding this issue?
Thanks,
Peter
 
 
 
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RE: Circuit Breaker Tripping Dring Fault Tests

[Jim Eichner]

I've been trying to solve this one myself.  I work with one pair of standards
(UL458 / CSA107.1) where they specifically say that opening the branch circuit
protection is acceptable during component fault testing, but NOT during short
circuit tests done for the purposes of validating inadequate trace spacings
(an easement offered in the standards in some situations).  I've always been
puzzled why we can't rely on branch circuit protection for both situations,
but neither agency has been able to explain the difference to me.
 
Jim Eichner, P.Eng.
Regulatory Compliance Manager
Xantrex Technology Inc.
phone: (604) 422-2546
fax: (604) 420-1591
e-mail: jim.eich...@xantrex.com
web: www.xantrex.com 
Confidentiality Notice: This email message, including any attachments, is for
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privileged information. Any unauthorized review, use, disclosure or
distribution is prohibited. If you are not the intended recipient, please
contact the sender by reply e-mail and destroy all copies of the original
message.


From: peter merguerian [mailto:pmerguerian2...@yahoo.com]
Sent: Tuesday, January 28, 2003 11:54 AM
To: emc-p...@majordomo.ieee.org
Subject: Circuit Breaker Tripping Dring Fault Tests



Dear All,

For safety, it is not clear from the standards whether the main branch circuit
breaker tripping during fault conditions is an acceptable result.

I see no reason why this should not be acceptable. What is your view? Some
third party labs find it acceptable and others do not.

Anyone can lead me to some inernational decisions regarding this issue?

Thanks,

Peter

 

 




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