Hi Stephen:
I think I missed the beginning of this thread, so
please forgive me if I rehash old ground.
The 'vertical line' and 'circle' you refer to, are
actually a 1 (One) and 0 (Zero); as in digital
logic on/off respectively.
My original posting on this subject
Hi Serge:
O = Out of Circuit
I = In Circuit
Note: while many people believe the symbols are O 1, they are in fact
O I
IEC 60417 Symbols 5007 and 5008 are neither:
the numbers 1 and 0, nor
the letters I and O.
They are the symbols depicted in the 60417
Hi Neil:
The origin may be true, but IEC60417 is quite clear. ON is a vertical line
(symbol 5007) and OFF is a circle (symbol 5008).
Agreed.
And thank you for the clarification.
Best regards,
Rich
---
This message is from the IEEE EMC
A week or so ago, I asked about the origin of the
0 and 1 symbols for off and on.
I mentioned that it was my recollection that the
the symbols came from early safety standards where
the off and on functions were by means of a
rotary switch where the 0/zero position was off.
I found some
I am looking for the origin of the power symbols
0 (off) and 1 (on).
The earliest standards that I have are CEE 10
and similar where the standard specifies something
like:
Where a rotary switch is used for power,
the 0 position shall be off and the 1 and
higher position shall be
Hi Richard:
What is a good source that explains the rational for the values for creepage
distances?
There was a good deal of research done in the late
'70s and early '80s on creepage distances and the
deterioration due to deposition of foreign materials
and the effects of humidity.
Hi Tom:
With a bit further search, I found:
http://w3.hike.te.chiba-u.ac.jp/iec417/html/doc/5180.html
This site specifies the use and the referring
standard:
Application: On any kind of equipment. To
identify equipment meeting the safety
requirements specified for class
Hi Tom:
I guess what you think is IEC 60417 No. 5180, which shows III
in diamond shaped frame (45 degree rotated square).
(http://member.nifty.ne.jp/tsato/terms/iec417-5180.gif)
Yes, this is the mark that was mentioned
to me.
However, I don't know which standard require the
A colleague recently showed me a Class III
identification mark. However, he had no
further information about the mark.
(The Class III mark would be used to identify
a Class III product similar to the way the
Class II mark square-within-a-square is used
to identify a double-insulated
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If you have any questions or comments about
Hi Gert:
I also tried the discharge between two fingers, and found the result to
be unpleasant at least.
Time to change standards...
Now we must ask the question:
Is the purpose of the standard to prevent
injury or to prevent an unpleasant experience?
I presume that
Hi Gert:
I also tried the discharge between two fingers, and found the result to
be unpleasant at least.
Time to change standards...
Now we must ask the question:
Is the purpose of the standard to prevent
injury or to prevent an unpleasant experience?
I presume that
Hi Tom:
So, for voltage up to 450V d.c. (i.e. up to 318V a.c.), capacitor
up to 0.1uF will become a Limited Current Circuit, hence the voltage
is not Hazardous Voltage (1.2.8.4) - no additional condition would
be required for the capacitor connected to the primary circuit.
Hi Rob:
I am in discussions with a potential supplier of IT equipment, Its our
usual policy to request testing to a listed standard
such as UL 60950 for safety in North America.
The supplier has replied that this is not mandatory.
Is he correct? what compels safety
Hi Tom:
So, for voltage up to 450V d.c. (i.e. up to 318V a.c.), capacitor
up to 0.1uF will become a Limited Current Circuit, hence the voltage
is not Hazardous Voltage (1.2.8.4) - no additional condition would
be required for the capacitor connected to the primary circuit.
Hi Rob:
I am in discussions with a potential supplier of IT equipment, Its our
usual policy to request testing to a listed standard
such as UL 60950 for safety in North America.
The supplier has replied that this is not mandatory.
Is he correct? what compels safety
Hi Tom:
Is it permitted to use PTC as an overcurrent protective device
for power sources not inherently limited?
I don't have EN60950-1 here, but I remember it must be a fuse
or other non-autoreset device.
I said:
The trick is to determine if your test houses can
Hello from San Diego:
One of our subscriber colleagues has pointed out that
my assertion that Europe uses yellow as the color of
the earthing wire is incorrect.
I recall when the green-yellow was agreed to for
power cords and internal equipment wiring. My
recall was that both yellow and
Hi Greg:
Why does True SELV require basic insulation
between SELV and earth?
What is the hazardous voltage source, and what
is the current path through the body if that
basic insulation should fail?
I believe (and I could be wrong) that it's a
Hi Alex:
We use a linear (basically a transformer with a PTC thermistor) class II
SELV O/P stand alone power supply rated 10Vac, 5A. One of the labs tested
the O/P Isc with a direct application of the sc. The other lab tested the
O/P Isc by applying a load of 8A. The results were
Hi Peter:
What is the percentage of color over a surface area for the insulated
green/yellow earthing conductor. Is it better to have more yellow than green
or more green than yellow. I know North Americans prefer more green than
yellow and Europeans like more yellow than green.
Hi John:
True SELV . requires double or reinforced insulation from hazardous
live parts/parts at hazardous voltages [different expressions used for
the same things] and basic insulation from earth. '950 SELV' allows SELV
circuits to be earthed (see 2.2.3.3 of IEC60950:1999 or
Hi John:
You may come across some distributors in Norway asking for DI or RI
between PRI-EARTH, even for Class 1 power supplies.
That's because Norway uses the 'IT' power distribution system, where
neither mains conductor is earthed directly, but one is earthed through
a
Hi John:
That depends on which variety of SELV you mean. True SELV, as opposed to
'950 SELV', requires double or reinforced insulation from earth
Why?
Best regards,
Rich
---
This message is from the IEEE EMC Society Product Safety
Hi John:
Y-caps have enough margin to easily withstand
the 4300 V dc without damage.
Without immediate failure, no doubt. But such a huge overstress may
cause latent damage that later results in failure, and, since IEC 60384
doesn't call for such an over-voltage test,
Hi Brian:
What I've always wondered about, at least for class 1 construction, is just
what is really being tested by the pri/sec hi-pot, when the customer chooses
to ground the power supply's return.
(These comments presume the secondary is SELV.)
When you use a ground for safety
Hi Brian:
I am attempting to comply with both the letter and spirit of 60950:2000, cl
5.2. Note that 5.2.2 allows for separate testing, according the type of
insulation required. When testing a (class 1) power supply, the withstand
level for primary to chassis is Basic; and for
Hi Tom:
In 60950, applicable clauses are 2.10.5.3 and 2.10.5.1 (I'm not
reading genuine IEC/EN 60950, and I'm sorry if I'm wrong) -
the former states that distance through insulation would be applied
in such situation, and the latter set minimum thickness of 0.4mm
for
Hi Chris:
To me, it's sort of funny in that it just says that the Creepage and
Clearance distances do not apply on inner layers of void free PCBs.
That's nice; but I can't find where a distance is specified. I mean, I
would think that there should be some minimum distance between
Hi Chris:
To me, it's sort of funny in that it just says that the Creepage and
Clearance distances do not apply on inner layers of void free PCBs.
That's nice; but I can't find where a distance is specified. I mean, I
would think that there should be some minimum distance between
Hi Ged:
In transformers with REINFORCED INSULATION or DOUBLE INSULATION the
insulation between 1ary and 2ary windings shalll consist of -
- 1 insulation layer having thickness at least 1mm, or
- at least 2 insulation layers with total thickness not less than 0.3mm, or
- 3
Hi Kris:
The markings on the power supply are: (also as per UL file)
Date code
model number
electrical ratings
Class 2 transformer
The additional markings are:
CAUTION, Risk of electric shock and Dry location use only and Do not
expose to liquid, vapor, or rain
Hi Kris:
A product from manufacturer X is delivered with a (direct plug-in) power
supply from mftr Y to customers in Canada.
Regarding the power supply, it is UL approved + UL listed and has the UL
marking with C and US.
The warning marking on the power supply is only in
It has been some time since I have had to explain
or justify product safety activity to a high-level
manager-type. As others have said, it is fraught
with difficulties.
Success depends on first determining the mindset
of the person asking the question. I believe I
would first ask a
Hi Ron:
Two years ago, Jim Bacher presented my paper,
Equipotentiality and Grounding -- Deriviation
of Grounding Resistance for Equipment
at the IEEE EMC Symposium Product Safety Workshop.
This paper is available for download from the IEEE
PSTC Mindcruiser web site:
Today, a message was posted that violates IEEE
emc-pstc rules against advertising. Here is
our rule:
-
5. Blatant or overt advertising of goods or services is not permitted.
The listserver is provided as a service by the IEEE, whose policies
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Hewlett-Packard Company San Diego site is looking
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The major job function is that of advising product
designers on
1) innovative safeguards for new products, and
2) safety certification requirements for new
products.
The ideal
Hi Xing Weibing:
We can read from table 5A of IEC60950:1999:
Touch current limit for accessible parts and circuits not connected
to protective earth: 0.25 mA
question 1 : How does it (0.25mA) come from and what it is based on?
For grounded (Class I) equipment for the home, the UL
Hi Ted:
it seems that the low voltage used in the application is being
mistaken for low energy. Your garden variety alkaline manganese cell
has such a low internal resistance that it behaves as a little bomb when
shorted. Same with lithium battery technology. If the solar cell can
Hi Chris:
We use similar circuits.
The circuit is an inverter powered from SELV. The
inverter output is hazardous voltage. Usually, the
output is floating, but not always.
The output MAY be hazardous energy ONLY IF the SELV
is hazardous energy. If the SELV is hazardous energy,
the
regards,
Rich
From douglas_beckw...@mitel.com Tue Jun 4 09:35:39 PDT 2002
Subject: Re: UL 60950, Section 6.1.2.1
To: Rich Nute ri...@sdd.hp.com
Cc: rgeorger...@carrieraccess.com, emc-p...@majordomo.ieee.org
Date: Tue, 4 Jun 2002 12:27:52 -0400
Hi Rich,
A question. If you
The policy for emc-pstc postings allows for posting of
availability of used or surplus equipment commonly used
by subscribers to this listserver. (See the Charter
that was sent to you when you subscribed.)
However, the policy does not include advertising of
any kind.
So, how do we decide
Hi Richard:
For those who want to read the UL60950 Section 6.1.2.1, I have written the
specific parts of the section that I have questions on. Otherwise, here are
my questions and comments:
1) If the bridging components are left in place, do I still have to meet the
10 mA
The subject matter for this forum is
product safety
EMC
telecom
and related issues.
Off-topic postings dilute the value of this forum
and are discouraged.
I am declaring the subject of guns as off-topic.
Further discussion of this topic may result in
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Hi Doug:
Thanks for sharing your findings on insulating tape
and anti-static tape.
All insulators have the property of insulation
resistance. Modern insulations have insulation
resistances in the gigaohm and teraohm ranges.
I would guess that anti-static insulators have a
relatively low
Hi John:
Now we have sub-classes Y1 to Y4. Y capacitors can be used in locations
where neither side is grounded, but in the OP's context, grounding is
involved.
What are the definitions of the various Y
capacitors in the most edition of IEC 384?
OP?
A Y-cap can be used
Hi John:
Ground connections is usually nice to have when dealing with EMC. But what
about EMC and a class 2 (double insulation) power supply (shall comply with
MIL-STD-461E) . I'm thinking on, what to do with the regularly Y-caps,
does it really have any meaning with these
Hi Chris, Bill, and all other subscribers:
A message with the subject:
A very nice game
was sent to the IEEE (emc-pstc) for posting by
our listserver.
The original message contained a virus known
as KLEZ.G.
The IEEE computer detected the virus.
This virus was stripped from the
Hi Amund:
Being a safety guy and not an emc guy... (disclaimer)
Ground connections is usually nice to have when dealing with EMC. But what
about EMC and a class 2 (double insulation) power supply (shall comply with
MIL-STD-461E) . I'm thinking on, what to do with the regularly
use any plastic.
Best regards,
Rich
Rich Nute wrote:
The choice is yours. If your product is supplied by a
Limited Power Source, then you may use any plastic for the
enclosure. If your product is not supplied by a Limited
Power Source, then you must use V1 or better
Hi Doug:
I've only heard shortening the yellow light cycle
as an unconfirmed rumor. But I've been watching.
grin
According to our local newspaper, the San Diego Union-
Tribune, not only did the contract photo cops shorten
the yellow light, they also moved the sensors.
The
Hi David:
You probably already know this, but don't forget that the product will need
to pass temp tests during abnormals i.e., blocked vents.
I'm not sure if pass temp tests means compliance with
the heating requirements or the abnormal requirements,
so I offer this clarification.
Hi Paul:
Can anyone give me any information on whether a box with less than .33 cubic
feet needs to meet UL Flammability ratings?
I have been told this is true, but I can not find the location of that
information.
I believe the requirement you are referring to is
Sub-clause
Hi George:
I have a safety question for the group. I have a small (about 8 x 10 x 2
inch) piece of ITE equipment, SELV, enclosed in a plastic case, powered by
an external 12 volt brick from AC mains.
The problem is, the device tends to run a little hotter than desired.
Hi John:
I read in !emc-pstc that Rich Nute ri...@sdd.hp.com wrote (in
200202202227.oaa19...@epgc264.sdd.hp.com) about 'double-pole switching
and fusing', on Wed, 20 Feb 2002:
Tables 2E and 2F are invoked only by the Note 2
to Sub-clause 2.7.4.
A Note is informative
Hi John:
I read in !emc-pstc that Crabb, John jo...@exchange.scotland.ncr.com
wrote (in B6CD5947CF30D411A1350050DA4B75FF03C2341C@sgbdun200.scotland.n
cr.com) about 'South Korean Power System', on Wed, 20 Feb 2002:
Typically I would expect IT equipment to be safe if line and
Hi Chris:
1. Can anyone else verify the breakdown voltage of 1Megavolt/meter for
air? Seems different than what I can remember; but I don't have a
reference handy. It also seems to me that this would be very dependent
upon humidity and pollution degree?
In a separate message,
Hi Scott:
The scope of EN 60825-1 says LEDs are included whenever the word laser
is used, meaning they are to be evaluated the same way lasers are. Does
this apply to status indicating LEDs (non-lasing)? If so, are
manufacturers expected to test every status-indicating LED on
Hi Ed:
With few exceptions, most power distribution
systems have one pole of the supply, the
neutral, grounded. (Indeed, the definition
of neutral for single-phase systems is the
grounded conductor.)
In the IEC scheme of the world, a power
distribution system where the neutral is
A good source is http://kropla.com/electric2.htm
http://kropla.com/electric2.htm .
According to that site:
Japan100V50/60 Hz*
*Eastern Japan 50 Hz (Tokyo, Kawasaki, Sapporo, Yokohoma, and Sendai)
*Western Japan 60 Hz (Osaka, Kyoto, Nagoya, Hiroshima)
A request from your list administrators...
Except... I (and other classic Compuserve users) won't see these messages
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Compuserve can send. It LOOKS great - but please don't send HTML to the
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Cortland is
Hi Richard:
We may soon be privately labeling our products for a particular customer,
and I have a question concerning the EU Declaration of Conformity. We will
be shipping products to our customer's distribution center, and they will be
responsible for sales to their customers.
Hi Dan:
I have received no emails today. Did my subscription cease?
No, your emc-pstc subscription is not terminated.
Today is the most unusual day in the history of
emc-pstc in that there were no postings to the
listserver between 5:30 PM PST Tuesday and 11 AM
PST Wednesday.
I,
Hi Pierre:
Unfortunately, Hexamine is temporarely unavailable from IMSPLUS, and,
furthermore, this product cannot be sold outside the US.
If somebody knows another source, he's welcome !
I did a Google search and found at least one more source:
Hi Pierre:
Reading the standard, I understand that the cloth used on the front of the
loudspeaker (external to fire enclosure) has to be tested according the
tablet test (see Table 13).
As I recall (from the UL standard), the tablet is
hexamine.
I have purchased tablets from:
Hi Joe:
We have a customer that is concerned about how our product, laboratory
equipment, will respond to electromagnetic disturbances from a high speed
train that runs close to their lab. The customer states that the
disturbance will be around 0.7-1.2 m Teslar.
I believe you
Hi George:
However, for the U.S. OSHA establishes acceptable NRTLs, and the
CFR uses the words NRTL, so I do not see how an electrical
inspector could object to what the Federal Government has sanctioned.
The inspector must abide by the certifications
approved by the local
Hi Gregg:
My understanding if that:
where OSHA is applicable then UL or equivalent is mandatory.
True. However, replace UL or equivalent with NRTL.
where OSHA is not application then Local Code is mandatory - and LOCAL
Code
requires NRTL (UL or equivalent)
Not
Hi Gregg:
Let me start by asking one simple question - WHAT IS THE PURPOSE OF
CERTIFICATION?
1- to meet the legal requirement
2- help market the product
3- do the 'right thing'
4- not to kill anyone
5- make sure that the product is nor recalled
Most
Hi John:
But whichever method is adopted, the customer pays the bill eventually
and I
have more confidence in the highly competitive world of electronic
products
to come up with a cost-effective solution in a timely manner.
One of the USA's major objections to
Hi Keith and Ghery:
There are a number of effects of harmonic current
emission from non-linear loads.
1) When a large number of loads rich in triplen
harmonics are supplied from a 3-phase source,
the neutral current can be as high as root 3
of the phase current. (This effect
Hi Amund:
I suggest you and your client and the regulatory
authority meet to address the situation.
Here are the issues as I understand them from your
message:
1. In idle mode, the emissions are comfortably
below the maximum allowed emissions.
2. In transmit mode, the emissions
Hi Pierre:
You did not state whether or not your secondary circuit
is intended to be SELV or not. This is critical to your
choice of capacitor. However, you did ask whether the
circuit is equivalent to reinforced insulation, so I
assume that your secondary circuit is SELV.
By
Taking John Woodgate's usual response to such
an inquiry, I did a Google search on inrush.
Surprisingly (to me), there is a wealth of
reasonably good info on the web under the subject
of inrush, including switches rated for inrush
current.
Best regards,
Rich
Hi Chris, Andrew, Carmen:
With regard to safety, both effects of altitude
must be considered:
1) effect of air pressure on the electric
strength of air (clearance), and
2) effect of lower density air on the
temperature of solid insulation.
(Creepage is a
No, it's simply that it isn't considered reasonable to have a radio and
a CFL in close proximity. If you want a lamp and a radio close together,
use an incandescent lamp.
That's the bottom line, isn't it?
Somebody has decided for me (in terms of
what is reasonable) that if I use a
Hi John:
I've replaced the incandescent lamp on my bedside
table with a new energy-saving compact flourescent
lamp. With the lamp on, I cannot listen to even
the strongest AM radio station on my clock radio
(on the same bedside table) due to the lamp
interference.
Hi Ken:
Trial lawyers and their clients have an obvious interest in portraying
consumers as helpless and child-like, and rich corporations as robber-barons
preying on the poor and weak. But why does the rest of society jump on that
bandwagon? Because profit and wealth, once
Hi Ken:
The Forrestal incident occurred during the Vietnam conflict, July 1967. It
was pretty much as you describe except I would not say EMI was not
controlled. All DOD services had EMI requirements at his time. In fact,
1967 was the year that MIL-STD-461 was adopted as a
Hi George:
The key word in EMC is compatibility. This implies that electrical and
electronic
equipment are (ideally) designed so that each can operate normally in the
presence
of another. This requires limiting both the emissions and sensitivity of
such
devices.
EMC?
Hi John:
Is there a value (or range of values) for the
resistance of water?
The data exists; it depends, of course, on solute nature and
concentration. Try a web search.
I did a web search before my post. There is lots of
data on the use of water resistance and
Hi Jason:
Water comprises a 3-dimensional resistor.
The value of the resistor depends on:
* the purity of the water itself (the
resistance is inversely proportional to the
purity);
* the dimensions of the electrodes (i.e., the
conductors in contact with the
Hi Cortland:
One can also use a pair of probes known to be well balanced and take the
difference between the A and B channels, or
use a differential input accessory or plugin. There is then no possibility
of high-voltage on the instrument chassis.
Balance is really
Hi Xing Weibing:
2. supply the SMPS from an isolating transformer where
both supply conductors are isolated from ground.
3. connect secondary's ground and primary 's ground (neutral and ground
are connected together)
This is the correct connection for measuring the
Hi Xing Weibing:
One of the problems of making oscilloscope measurements
within switching-mode power supply circuits is that the
common side of the oscilloscope *MAY* change the waveform.
There are two ways to minimize the effect of the common
side of the scope from affecting the waveform:
Hi John:
More significantly, its resistance affects the maximum short-circuit
current that can flow.
This is a valid consideration with regard to safety.
Given a 6-amp maximum, 0.75 sq mm size, and 2 meters
length.
In North America, 2X rated current is the 1-minute
operating time
For an IT product there is a restriction in the use of mains cords with a
cross
sectional area of 0.75mm2 for units up to 6 amps when the cord is greater
than
2m in length (EN60950: 2000 section 3.2.5)
I am curious as to the hazard that is prevented by
this length
Hi Xing Weibing:
Here is my answer to the question.
Hi group I have a question regarding clearance and working voltage of
IEC60950. If I HAVE A AC ADAPTER(AC 100-240V 50/60Hz) ,THE WORKING
VOLTAGE MEASURED ARE AS FOLLOWS: Nominal supply voltage: AC240V PRIMARY
AND SECONDARY :
On the aspect of the where to put Product Safety/Compliance in the
organization discussion bears mentioning on the forum. In general I
advocate that the Product Safety/Compliance department be separate from
Engineering, Sales, and Operations. The Safety/Compliance group should
Hi Jerry:
Will a production line hipot test be required?
As far as I know, the only certification house that
requires a production-line hi-pot test of TNV circuits
is UL. The test is specified in the gray pages as a
separate test from that of the mains hi-pot test.
Since you
Hi Dan:
Dell Computers, as well as a few other major players, take a proactive
approach to compliance and actually have a VP position for compliance. With
a little investigation into the benefits of having a first rate compliance
department with the ability to design for
Hi Alan:
Two questions, does the group see a time when we have a VP Compliance on
level terms with VP Finance, VP Marketing etc, or is this already
happening in the US.
No. And not likely to happen in companies with ordinary
products.
As a general rule, compliance is seen as a
Over the years, this listserver has never had a problem
with decorum. We have had no rules addressing decorum.
I and the other administrators do have expectations for
decorum in posted messages. Here are our expectations.
Decorum:
-Propriety and good taste in conduct or appearance.
Hi John:
It seems to me that the actual word 'tetanus' is not used for this in
Britain, maybe because of the risk of confusion with the infection.
Reilly uses the word tetanus.
Guyton uses the word tetanization.
Tetanization would seem a better choice of
word to describe the
Hi John:
Also consider that the rectifier will very probably fail due to
excessive reverse voltage under the fault condition, thus allowing fault
current to flow through the transformer winding.
Will the rectifier fail open or short?
This SELV grounding scheme certainly doesn't
Hi John:
I presume that the fault current path for the ungrounded
SELV pole must be routed through the SELV source to ground
as that path is the lowest impedance path to ground. It
seems to me that the fault current would have to pass
through the transformer winding. In
Hi John:
SELV can protect under single fault conditions. BUT, as I tried to
explain, under some conditions, it can allow a single fault *to persist
undetected*, until eventually a second, unrelated fault occurs which
then results in a serious hazard.
This is a
Hi Vito:
Could either of you clarify why a double insulated SELV circuit can not be
grounded? Is it a 60950 based or based on some other performance(?) based
requirements?
This requires a bit of history. I don't have all of
the history, but I can fill in some of the blanks.
IEC
Hi John:
My point is that, if attention-demanding words of differing intensity
are considered necessary, how can they be chosen, other than the way
they are at present?
Of course, you may deny that differing intensity is necessary, so that
only one word is required, but I
Hi Ted:
The electrician's rule of thumb when working on domestic wiring was to
always check the wire is dead, even though you isolated it, in case of
bridging or faulty connection. The technique used was to brush the
exposed conductor lightly with the back of the fingers. Any
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