Re: PoE injectors

[emc-p...@ieee.org]

In message <002101c9b6bf$ca409a50$d600a...@tamuracorp.com>, dated Mon, 6 
Apr 2009, Brian O'Connell  writes:

>When you refer to "mains circuits", does this mean the 'mains' power 
>that enters the building, or is the individual distribution 
>circuit/node being reference ?
>
>Do you mean that a fuse, for an indvidual appliance, is better for 
>protection from fire than a breaker ?

No, this is a very specific case, of 'power cross' on to thin data 
cables. If the data cable conductors are ground-referenced (PELV), the 
cable may overheat because the fault current is not sufficient to clear 
a fuse or over-current breaker, but is very unlikely to be insufficient 
to operate a GFCI or RCD.

If the data cable conductors are not ground referenced (SELV), then the 
'power cross' can remain undetected, probably until someone touches the 
SELV circuit.
-- 
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
Things can always get better. But that's not the only option.
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

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RE: PoE injectors

[emc-p...@ieee.org]

When you refer to "mains circuits", does this mean the 'mains' power that
enters the building, or is the individual distribution circuit/node being
reference ?

Do you mean that a fuse, for an indvidual appliance, is better for protection
>from fire than a breaker ?

thanks,
Brian 

 > -Original Message-
 > From: emc-p...@ieee.org [mailto:emc-p...@ieee.org]On Behalf Of John
 > Woodgate
 > Sent: Monday, April 06, 2009 1:47 AM
 > To: Piotr Galka
 > Cc: EMC-PSTC
 > Subject: Re: PoE injectors
 > 
 > In message <79BF8E9B82E143448258D4EBCD718037@MmPc21>, dated 
 > Mon, 6 Apr 
 > 2009, Piotr Galka  writes:

 > I explained that if there is accidental contact between an 
 > SELV circuit 
 > in a building and a power circuit, the SELV circuit can go to, and 
 > remain indefinitely at, full mains voltage. While the probability of 
 > such an event is very low, the consequences may be fatal.
 > 
 > >and less risk of fire.
 > 
 > Yes, less risk of fire if the mains circuits are protected 
 > by fuses, not 
 > RCDs or GFCIs.
 > -- 
 > OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
 > Things can always get better. But that's not the only option.
 > John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

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Re: PoE injectors

[emc-p...@ieee.org]

John,

- Original Message - 
From: "John Woodgate" 

> I explained that if there is accidental contact between an SELV circuit in 
> a building and a power circuit, the SELV circuit can go to, and remain 
> indefinitely at, full mains voltage.

Everything clear.
I didn't considered such scenario (forgot you have written that).

To solve both scenarios SELV should be not grounded, but each device should 
start an alarm seeing mains at its SELV - the best way to extra complicate 
all devices.

Best Regards

Piotr Galka 

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Re: PoE injectors

[emc-p...@ieee.org]

In message <79BF8E9B82E143448258D4EBCD718037@MmPc21>, dated Mon, 6 Apr 
2009, Piotr Galka  writes:

>In my opinion in such installations SELV gives less risk of electric 
>shock

I explained that if there is accidental contact between an SELV circuit 
in a building and a power circuit, the SELV circuit can go to, and 
remain indefinitely at, full mains voltage. While the probability of 
such an event is very low, the consequences may be fatal.

>and less risk of fire.

Yes, less risk of fire if the mains circuits are protected by fuses, not 
RCDs or GFCIs.
-- 
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
Things can always get better. But that's not the only option.
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

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Re: PoE injectors

[emc-p...@ieee.org]

John,

- Original Message - 
From: "John Woodgate" 
>
> In most countries, that technique (TN-C-S) is used only if the combined 
> neutral and grounded conductor is grounded at many places, so that if it 
> breaks, load current is distributed among the grounding points and remains 
> at safe values in all conductors.

Currently only 3-wire installations are made here, but I was speaking about 
old ones. Even if each flat had its own grounding the problem can appear 
between rooms, specially because there were no direct connection from main 
entrance point to each socket, but there were plenty connections on the way 
in the connection boxes under the ceiling over each socket.

> Your point, effectively about SELV being preferred to PELV where the power 
> circuit protection is by fuses, is valid, being the lesser of two evils 
> (increased risk of electric shock, versus increased risk of fire, if 
> segregation is violated).

I disagree (or I misunderstood). In my opinion in such installations SELV 
gives less risk of electric shock and less risk of fire. I see the question 
should be: How more safety PELV gives in new installations and how less in 
old ones. Then these coefficients should be multiplied by the ratio of new 
installations to old installations and at some date will be (or was been) 
the point when PELV becomes statistically more safety, but it is really hard 
to count it.

Piotr Galka 

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Re: PoE injectors

[emc-p...@ieee.org]

In message <00AEA30D28014979B44664EAB0477931@MmPc21>, dated Sat, 4 Apr 
2009, Piotr Galka  writes:

>Consider electric installation with zeroing and not grounding. I'm not 
>sure how it is in another countries so to be precise grounding is the 3 
>wire installation, and zeroing is the 2 wire installation, but with 3 
>contact sockets (the grounding pin in each socket is connected with 
>neutral power cable).
>All house buildings older than about 10 years in Poland have zeroing 
>and not grounding.

In most countries, that technique (TN-C-S) is used only if the combined 
neutral and grounded conductor is grounded at many places, so that if it 
breaks, load current is distributed among the grounding points and 
remains at safe values in all conductors.

Your point, effectively about SELV being preferred to PELV where the 
power circuit protection is by fuses, is valid, being the lesser of two 
evils (increased risk of electric shock, versus increased risk of fire, 
if segregation is violated).
-- 
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
Things can always get better. But that's not the only option.
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

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Re: PoE injectors

[emc-p...@ieee.org]

John and all,

> Can somebody explain to me why an isolated power supply is 'safer' than an 
> earthed one?

Consider electric installation with zeroing and not grounding. I'm not sure 
how it is in another countries so to be precise grounding is the 3 wire 
installation, and zeroing is the 2 wire installation, but with 3 contact 
sockets (the grounding pin in each socket is connected with neutral power 
cable).
All house buildings older than about 10 years in Poland have zeroing and not 
grounding.
When it happens that the neutral power cable is broken than if any one 
device is on (nowadays plenty devices are on in standby mode) than this 
device connects live 230V power to your grounding system. All devices metal 
cases becomes "grounded" to 230V.
This is specially a problem in old buildings with aluminium wires ("Big 
Brother" who decided about all in Poland, in hopefully past times, decided 
aluminium installations are cheaper and you had no chance to do another 
way).
If it happens it is danger, but as all metal cases are at the same 230V 
potential you have a chance to survive.
Now consider the SELV circuit which is not only isolated but also grounded 
in one of your devices and the SELV cable goes to another place in the same 
building, where there is everything OK with power (it may be your another 
room). At this SELV circuit there is 230V against all metal cases someone 
can tough at the same time he touches something connected with this SELV. 
I'm not sure if it is any sense to install differential breakers in such 
installation, but even one is there it will not see that current as 
differential.

In my opinion until 100% of electric installations all over the world will 
be 3 wire the isolated SELV is more safely then isolated and grounded (if 
grounded is understand as connected to socket grounding pin).
But I'm certainly not an expert in safety issues.

Best Regards

Piotr Galka


- Original Message - 
From: "John Woodgate" 
To: 
Sent: Friday, March 27, 2009 9:39 AM
Subject: Re: PoE injectors


> In message <6.1.0.6.2.20090327004517.030f4...@pop.randolph-telecom.com>, 
> dated Fri, 27 Mar 2009, Joe Randolph  writes:
>
>>A Class 2 supply is the most common type of supply that I have seen for 
>>POE injection. And yes, the output should be isolated from earth ground to 
>>comply with IEEE 802.3af.
>
> Can somebody explain to me why an isolated power supply is 'safer' than an 
> earthed one? I am particularly concerned that this applies to IT networks 
> and anything else that may run through, for example, roof voids and 
> similar spaces. Within one room, as for Class II consumer products, the 
> techniques is probably acceptable.
>
> I know there are 'segregation' requirements, but cable runs can be 
> disturbed by non-electrical people during maintenance. The point is that 
> cable damage (by humans, rodents or building movements) can create a 
> connection between live mains and the 'SELV' circuit. Since the latter is 
> not earthed, the fault can persist indefinitely, until someone contacts 
> the SELV circuit. The hazard is great, the probability is low, and to me 
> that results in a tick in the 'unacceptable risk' box.
>
> We now have the concept of 'PELV', protected extra-low voltage, which has 
> reinforced insulation from mains voltage AND is earthed (preferably at one 
> point only, to avoid currents due to earth potential differences. I think 
> that all 'SELV' requirements must be re-examined to see if they should be 
> changed to 'PELV'. In hazard-based terms, there is no contest. SELV has 
> two safeguards, PELV has three.
>>
>>Personally, I do not see any safety compliance problems with this 
>>construction when used as intended (inside lines).
>>
>>By the way, one problem that I *have* seen with this construction is 
>>performance related. Most of these POE injection power supplies are 
>>switching converters, and the Y-caps used on the input for EMI suppression 
>>create a voltage divider that places a very high 50/60 Hz common mode 
>>noise signal (typically one half of the AC mains voltage) on the Ethernet 
>>outputs.
>
> How can Y-caps do that? Y caps go from both mains poles to earth.
>
>>This means that an IP telephone powered by the POE injector will be riding 
>>on the 50/60 Hz common mode noise. The analog audio circuits in the IP 
>>phone, such as the microphone for a hands-free mode, can be sensitive to 
>>this common mode noise and produce audible hum.
>>Grounding the chassis of the POE injector fixes the problem, but most of 
>>these devices are ungrounded.
>
> Then they cannot possibly have Y-caps.
>
>>So, the 

Re: PoE injectors

[emc-p...@ieee.org]

In message , dated Sat, 28 Mar 2009, 
John Woodgate  writes:

>I don't think I came even close to making that mistake.

Oops! I misread your message. I thought you were referring to multiple 
grounds on the POE cable.

What I see you DO mean is that if there is a mains-to-POE short at a 
long distance from the POE sender, the fault current might not be enough 
to trip the mains circuit protection but enough to overheat the cable. 
Yes, it might, but I would hope that the protection these days is not a 
fuse but an RCD/GFI, in which case the trip current does not cause 
overheating.
-- 
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
Things can always get better. But that's not the only option.
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

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Re: PoE injectors

[emc-p...@ieee.org]

In message <49cd7a6d.3020...@itesafety.com>, dated Fri, 27 Mar 2009, 
Robert Johnson  writes:

>Earthing the output of a power source is one way of preventing faults 
>within the source between mains to output from energizing the output. 
>It quickly overloads and opens the mains circuit.

Indeed.

>Relying on an earthing for protection of a signal circuit which runs 
>any distance from the source to protect it from mains short is unwise. 
>It is unlikely to operate overcurrent protection and may cause fires. 
>For example typical cat 5 wire (24AWG) is 0.088 ohms/meter which means 
>lengths approaching 100m would not operate branch circuit protection 
>but simply overheat.

I can't visualize a scenario in which that would occur. I'm certainly 
not suggesting grounding the POE at a distance from the sender.

>Isolation of signal circuits from mains must be done by insulation and 
>separation, even when worried about rodent damage and other misuse.

Those measures are necessary, yes.

>Expecting earthing to protect from mains shorts for any long light 
>gauge wire is a mistaken concept.

I don't think I came even close to making that mistake.
-- 
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
Things can always get better. But that's not the only option.
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

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Re: PoE injectors

[emc-p...@ieee.org]

Hi, Joe.

On 27 Mar 2009 at 0:59, Joe Randolph wrote:
> 
> On 3/26/2009, Peter Tarver wrote:
> 
> > What if the power supply is Class 2 Equipment?
> 
> Hi Pete:
> 
> A Class 2 supply is the most common type of supply that I
> have seen for POE injection. And yes, the output should be
> isolated from earth ground to comply with IEEE 802.3af.
> 
> Personally, I do not see any safety compliance problems with
> this construction when used as intended (inside lines).

I was specifically responding to neve...@comcast.net 
statement:

> 2) The power supply in the sourcing equipment are 
>isolated per IEEE 802.3 (1500Vrms).

in the context of Class 2 Equipment type power supplies 
needing (typically) 3 kV isolation to the AC Mains.  This 
is indeed safe and presents no issues.  I simply wanted to 
make certain that no one mistakenly assumed 1.5 kV 
isolation was all that might ever be required.  Probably a 
knee-jerk reaction on my part, since neve...@comcast.net 
probably already knows this.

Keep in mind, also, that there're differences between a 
Class 2 power supply, in the NEC sense, and a Class 2 
Equipment power supply, in the 60950-1 sense.  Between your 
wording and Robert Johnson's post, I'm not sure which you 
meant, though that doesn't matter much.


Peter Tarver
ptar...@ieee.org

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Re: PoE injectors

[emc-p...@ieee.org]

Earthing the output of a power source is one way of preventing faults within
the source between mains to output from energizing the output. It quickly
overloads and opens the mains circuit.
Relying on an earthing for protection of a signal circuit which runs any
distance from the source to protect it from mains short is unwise. It is
unlikely to operate overcurrent protection and may cause fires. For example
typical cat 5 wire (24AWG) is 0.088 ohms/meter which means lengths approaching
100m would not operate branch circuit protection but simply overheat.
Isolation of signal circuits from mains must be done by insulation and
separation, even when worried about rodent damage and other misuse.
Expecting earthing to protect from mains shorts for any long light gauge wire
is a mistaken concept.

Bob Johnson
ITE Safety  

John Woodgate wrote: 

In message <6.1.0.6.2.20090327004517.030f4...@pop.randolph-telecom.com>
 , dated
Fri, 27 Mar 2009, Joe Randolph 
  writes: 



A Class 2 supply is the most common type of supply that I have 
seen for POE
injection.  And yes, the output should be isolated from earth ground to comply
with IEEE 802.3af. 



Can somebody explain to me why an isolated power supply is 'safer' than 
an
earthed one? I am particularly concerned that this applies to IT networks and
anything else that may run through, for example, roof voids and similar
spaces. Within one room, as for Class II consumer products, the techniques is
probably acceptable. 

I know there are 'segregation' requirements, but cable runs can be 
disturbed
by non-electrical people during maintenance. The point is that cable damage
(by humans, rodents or building movements) can create a connection between
live mains and the 'SELV' circuit. Since the latter is not earthed, the fault
can persist indefinitely, until someone contacts the SELV circuit. The hazard
is great, the probability is low, and to me that results in a tick in the
'unacceptable risk' box. 

We now have the concept of 'PELV', protected extra-low voltage, which 
has
reinforced insulation from mains voltage AND is earthed (preferably at one
point only, to avoid currents due to earth potential differences. I think that
all 'SELV' requirements must be re-examined to see if they should be changed
to 'PELV'. In hazard-based terms, there is no contest. SELV has two
safeguards, PELV has three. 



Personally, I do not see any safety compliance problems with 
this
construction when used as intended (inside lines). 

By the way, one problem that I *have* seen with this 
construction is
performance related.  Most of these POE injection power supplies are switching
converters, and the Y-caps used on the input for EMI suppression create a
voltage divider that places a very high 50/60 Hz common mode noise signal
(typically one half of the AC mains voltage) on the Ethernet outputs.  



How can Y-caps do that? Y caps go from both mains poles to earth. 



This means that an IP telephone powered by the POE injector 
will be riding
on the 50/60 Hz common mode noise.  The analog audio circuits in the IP phone,
such as the microphone for a hands-free mode, can be sensitive to this common
mode noise and produce audible hum.  

Grounding the chassis of the POE injector fixes the problem, 
but most of
these devices are ungrounded.  



Then they cannot possibly have Y-caps. 



So, the IP telephone has to be designed with an extraordinary 
level of 50/60
Hz common mode immunity in order to avoid hum in the analog audio path. 



It sounds as though people are making some fundamental error that shows 
up as
this problem. 


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Re: PoE injectors

[emc-p...@ieee.org]

In message <6.1.0.6.2.20090327120836.030f3...@pop.randolph-telecom.com>, 
dated Fri, 27 Mar 2009, Joe Randolph  writes:

>I will try to explain the mechanism, but I don't want to take this 
>thread too far off track. 

OK, I've replied off-list.
-- 
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
Things can always get better. But that's not the only option.
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

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Re: PoE injectors

[emc-p...@ieee.org]

On 3/27/2009, John Woodgate wrote:




How can Y-caps do that? Y caps go from both mains poles to earth. 



Hi John:

I will try to explain the mechanism, but I don't want to take this thread too
far off track.  Most of the discussion here has been about the safety aspects
of POE.  My comment about common mode noise was an aside, since it does not
relate to a safety issue.  It's simply a consequence of using POE injectors
that have an ungrounded chassis. 

Perhaps I used the term "Y caps" too loosely.  The caps I refer to are
Y1-rated safety caps that connect from each side of the AC mains input to the
internal chassis of the POE injector.  You are correct that these caps do not
actually connect to earth ground in a Class 2 arrangement.  They would only
connect to ground if the chassis were grounded, and it is the ungrounded
chassis that causes the problem.  With the chassis floating, the two caps
create a voltage divider.  If one side of the AC mains is grounded, the entire
chassis rides on the center point of the capacitive voltage divider, and with
respect to earth, it carries a 50/60 Hz potential of one half the AC mains
voltage.

All of this is a high impedance circuit and there are no dangerous touch
currents involved, but since the Ethernet cable is also floating with respect
to earth, the 50/60 Hz noise typically carries through to the Ethernet output
via similar EMI caps in the second power supply that generates the DC applied
to the Ethernet port within the POE injector.  An IP phone that is powered
exclusively by an ungrounded POE injector will typically be floating on this
very large (but high impedance) common mode noise.

In theory, a floating IP phone will be immune to this common mode noise, but
there are parasitic capacitances to earth that allow small common mode
currents to flow.  I have seen this become a problem for the microphone input
of the hands-free mode. 





Joe Randolph
Telecom Design Consultant
Randolph Telecom, Inc.
781-721-2848 (USA)
j...@randolph-telecom.com
http://www.randolph-telecom.com  

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Re: PoE injectors

[emc-p...@ieee.org]

In message 
<201048ea81ba0745aca78e4cc883900104781...@desmdswms201.des.grplnk.net>, 
dated Fri, 27 Mar 2009, "Haynes, Tim (SELEX GALILEO, UK)" 
 writes:

>Does this change the circuit for SELV to PELV and I thought that PELV 
>and SELV circuits could not be  "mixed and matched" as the SELV circuit 
>safety is partially dependant on there NOT being an earth?

That is indeed the 'phlogiston theory of electrical safety'.(;-) How can 
adding a THIRD safeguard to an SELV source make it unsafe?

I suspect that somewhere in the history of SELV, 'no earth is required' 
was modulated into 'no earth shall be present', for no reason.
-- 
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
Things can always get better. But that's not the only option.
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

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RE: PoE injectors

[emc-p...@ieee.org]

John, All,

I know nothing about PoE or IT systems as such but...

>Grounding the chassis of the POE injector fixes the problem, but most 
>of these devices are ungrounded.

Does this change the circuit for SELV to PELV and I thought that PELV
and SELV circuits could not be  "mixed and matched" as the SELV circuit
safety is partially dependant on there NOT being an earth?

Regards
Tim


SELEX Sensors and Airborne Systems Limited
Registered Office: Sigma House, Christopher Martin Road, Basildon, Essex SS14
3EL
A company registered in England & Wales.  Company no. 02426132

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Re: PoE injectors

[emc-p...@ieee.org]

In message <6.1.0.6.2.20090327004517.030f4...@pop.randolph-telecom.com>, 
dated Fri, 27 Mar 2009, Joe Randolph  writes:

>A Class 2 supply is the most common type of supply that I have seen for 
>POE injection.  And yes, the output should be isolated from earth 
>ground to comply with IEEE 802.3af.

Can somebody explain to me why an isolated power supply is 'safer' than 
an earthed one? I am particularly concerned that this applies to IT 
networks and anything else that may run through, for example, roof voids 
and similar spaces. Within one room, as for Class II consumer products, 
the techniques is probably acceptable.

I know there are 'segregation' requirements, but cable runs can be 
disturbed by non-electrical people during maintenance. The point is that 
cable damage (by humans, rodents or building movements) can create a 
connection between live mains and the 'SELV' circuit. Since the latter 
is not earthed, the fault can persist indefinitely, until someone 
contacts the SELV circuit. The hazard is great, the probability is low, 
and to me that results in a tick in the 'unacceptable risk' box.

We now have the concept of 'PELV', protected extra-low voltage, which 
has reinforced insulation from mains voltage AND is earthed (preferably 
at one point only, to avoid currents due to earth potential differences. 
I think that all 'SELV' requirements must be re-examined to see if they 
should be changed to 'PELV'. In hazard-based terms, there is no contest. 
SELV has two safeguards, PELV has three.
>
>Personally, I do not see any safety compliance problems with this 
>construction when used as intended (inside lines).
>
>By the way, one problem that I *have* seen with this construction is 
>performance related.  Most of these POE injection power supplies are 
>switching converters, and the Y-caps used on the input for EMI 
>suppression create a voltage divider that places a very high 50/60 Hz 
>common mode noise signal (typically one half of the AC mains voltage) 
>on the Ethernet outputs. 

How can Y-caps do that? Y caps go from both mains poles to earth.

>This means that an IP telephone powered by the POE injector will be 
>riding on the 50/60 Hz common mode noise.  The analog audio circuits in 
>the IP phone, such as the microphone for a hands-free mode, can be 
>sensitive to this common mode noise and produce audible hum. 
>
>Grounding the chassis of the POE injector fixes the problem, but most 
>of these devices are ungrounded. 

Then they cannot possibly have Y-caps.

>So, the IP telephone has to be designed with an extraordinary level of 
>50/60 Hz common mode immunity in order to avoid hum in the analog audio 
>path.

It sounds as though people are making some fundamental error that shows 
up as this problem.
-- 
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
Things can always get better. But that's not the only option.
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

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Re: PoE injectors

[emc-p...@ieee.org]

On 3/26/2009, Peter Tarver wrote:



What if the power supply is Class 2 Equipment?  Then the 
isolation requirements are somewhat larger than 1500 V.  
Also, doesn't the supplied power to the PD have to continue 
to be isolated from earth, as do the ethernet circuits? 



Hi Pete:

A Class 2 supply is the most common type of supply that I have seen for POE
injection.  And yes, the output should be isolated from earth ground to comply
with IEEE 802.3af.

Personally, I do not see any safety compliance problems with this construction
when used as intended (inside lines).

By the way, one problem that I *have* seen with this construction is
performance related.  Most of these POE injection power supplies are switching
converters, and the Y-caps used on the input for EMI suppression create a
voltage divider that places a very high 50/60 Hz common mode noise signal
(typically one half of the AC mains voltage) on the Ethernet outputs.  This
means that an IP telephone powered by the POE injector will be riding on the
50/60 Hz common mode noise.  The analog audio circuits in the IP phone, such
as the microphone for a hands-free mode, can be sensitive to this common mode
noise and produce audible hum.  

Grounding the chassis of the POE injector fixes the problem, but most of these
devices are ungrounded.  So, the IP telephone has to be designed with an
extraordinary level of 50/60 Hz common mode immunity in order to avoid hum in
the analog audio path.




Joe Randolph
Telecom Design Consultant
Randolph Telecom, Inc.
781-721-2848 (USA)
j...@randolph-telecom.com
http://www.randolph-telecom.com  

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Re: PoE injectors

[emc-p...@ieee.org]

On 25 Mar 2009 at 21:47, neve...@comcast.net wrote:
> 
> Does it matter for the discussion that:
> 
> 1) Power is not present at the output of the source unless
> the other side of the cable connects to a PD (powered
> device) which "signals" to the sourcing equipment it is a PD
> and to turn it on. If you unplug the PD, the power goes off.

The requirements apply for all load modes of operation, 
including when the handshaking is completed and the PoE 
output supplies power to the PD.

> 2) The power supply in the sourcing equipment are isolated
> per IEEE 802.3 (1500Vrms).

What if the power supply is Class 2 Equipment?  Then the 
isolation requirements are somewhat larger than 1500 V.  
Also, doesn't the supplied power to the PD have to continue 
to be isolated from earth, as do the ethernet circuits?

Peter Tarver
ptar...@ieee.org

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RE: PoE injectors

[emc-p...@ieee.org]

On 26 Mar 2009 at 9:00, Umbdenstock, Don wrote:
> 
> My apologies for thinking out loud “if a PD can present up
> to a 13 W load, then the 25k handshake cannot be part of the
> load, but rather is restricted to a handshake circuit. So
> the question is whether there is a spec for current limiting
> for PSE? If a PSE is by definition current limited, and AHJs
> know this, then LPS or NEC Class 2 marking wouldn't seem to
> be necessary. 

LPS, NEC Class 2, et al, all have voltage, current and 
possibly overcurrent protection and power limitations 
placed on them **at the source**.  The load becomes 
irrelevant to such circuit designations.

> The reason for the series of PoE comments is to anticipate
> the needs of the AHJs. Is the above conclusion a logical
> argument for anticipating questions from an AHJ?

PoE, to my knowledge, isn't recognized by AHJs.  They may 
try to impose a TNV type of designation, for their 
purposes, which they do recognize (I've heard of at least 
one case of this).

Peter Tarver
ptar...@ieee.org

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RE: PoE injectors

[emc-p...@ieee.org]

On 25 Mar 2009 at 23:17, Ron Pickard, RPQ wrote:
> 
> Hi Don,
> 
> Further to what Joe has stated below, according to IEC
> 60950-1 an ethernet interface circuit is generally
> characterized as an SELV circuit, but must also be
> considered a TNV-1 circuit if it is subject to overvoltages
> (atmospheric conditions).

Per one UL PAG, TNV classification does not apply, if the 
installation instructions state that the PoE system 
conductors do not allow such exposure; meaning they they 
remain indoors.

> You might also want to read
> through CENELEC CLC/TR 62102 (replaced ETSI EG 201212)
> entitled "Electrical safety - Classification of interfaces
> for equipment to be connected to information and
> communications technology networks"

Absolutely.  I have recommended to some TC 108 members that 
TR 62102 be updated to include PoE.  As of my last check 
(~FEB2008), it did not.

> Although with that said, LPS may more likely be more of a
> customer requirement rather than regulatory, whereby there
> should be an adequate selection of LPS and non-LPS PoE
> invertors. LPS selection should depend on a customer's
> specific requirements and the specific application. IMHO,
> for a safer installation, LPS PoE injectors should be
> considered.

There may be a semantic issue involved here.  The 1.3 A 
limit I mentioned previously applies at the PoE output of 
the product (e.g., the modular jack), not at the power 
supply's output.  I just wanted to be clear about that.


Peter Tarver
ptar...@ieee.org

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Re: PoE injectors

[emc-p...@ieee.org]

Does it matter for the discussion that:

1) Power is not present at the output of the source unless the other side of 
the cable connects to a PD (powered device) which "signals" to the sourcing 
equipment it is a PD and to turn it on. If you unplug the PD, the power goes 
off.

2) The power supply in the sourcing equipment are isolated per IEEE 802.3 
(1500Vrms).

?

Neven





From: "Don Umbdenstock" 
To: emc-p...@ieee.org
Sent: Wednesday, March 25, 2009 1:42:50 PM GMT -08:00 US/Canada Pacific
Subject: RE: PoE injectors

Let me share some of my thought process with you.

Hazard based consideration and 60950 would suggest that if a power
source (injector) can provide more than 15W, then a fire enclosure or
other means of fire protection is necessary.  Other means to prevent
fire when a fire enclosure is not provided includes LPS source, product
built with V-1 or better circuit boards, etc.

Most injectors provide more than 15W to be able to power more than one
device and handle line loss.  Thus it would seem intuitive that the PoE
injector (or switch) would be LPS.

What's the rest of the story that I'm missing?

Don
561 912  6440


From: Umbdenstock, Don 
Sent: Wednesday, March 25, 2009 4:34 PM
To: emc-p...@ieee.org
Subject: FW: PoE injectors


Hi Pat,

LPS means "limited power source" per 60950 Clause 2.5; this is the basis
of my question.

Don
561 912  6440

From: pat.law...@slpower.com [mailto:pat.law...@slpower.com] 
Sent: Wednesday, March 25, 2009 12:14 PM
To: Umbdenstock, Don
Cc: emc-p...@ieee.org
Subject: Re: PoE injectors

Hi Don,

What does 'LPS' mean in this context?

Pat Lawler
EMC Engineer
SL Power Electronics Corp.

"Umbdenstock, Don"  wrote on 03/25/2009 
07:23:54 AM:
> I have perused the IEEE 802.3af explanation on various web sites and
> examined supplier specs.  I came to the conclusion that the injector
> should be LPS certified and marked as such.  However, most of the 
> injectors I have found by web search do not indicate LPS.
> 
> Does anyone believe that a PoE injector does not require LPS 
certification? 
> If so, why not?
> 
> Regards,
> 
> Don Umbdenstock
> Manager Compliance Engineering
> 
> Tyco Safety Products / Sensormatic
> 6600 Congress Avenue
> Boca Raton, FL 33487 USA
> Phone: 561.912.6440
> djumbdenst...@tycoint.com

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RE: PoE injectors

[emc-p...@ieee.org]

Let me share some of my thought process with you.

Hazard based consideration and 60950 would suggest that if a power
source (injector) can provide more than 15W, then a fire enclosure or
other means of fire protection is necessary.  Other means to prevent
fire when a fire enclosure is not provided includes LPS source, product
built with V-1 or better circuit boards, etc.

Most injectors provide more than 15W to be able to power more than one
device and handle line loss.  Thus it would seem intuitive that the PoE
injector (or switch) would be LPS.

What's the rest of the story that I'm missing?

Don
561 912  6440


From: Umbdenstock, Don 
Sent: Wednesday, March 25, 2009 4:34 PM
To: emc-p...@ieee.org
Subject: FW: PoE injectors


Hi Pat,

LPS means "limited power source" per 60950 Clause 2.5; this is the basis
of my question.

Don
561 912  6440

From: pat.law...@slpower.com [mailto:pat.law...@slpower.com] 
Sent: Wednesday, March 25, 2009 12:14 PM
To: Umbdenstock, Don
Cc: emc-p...@ieee.org
Subject: Re: PoE injectors

Hi Don,

What does 'LPS' mean in this context?

Pat Lawler
EMC Engineer
SL Power Electronics Corp.

"Umbdenstock, Don"  wrote on 03/25/2009 
07:23:54 AM:
> I have perused the IEEE 802.3af explanation on various web sites and
> examined supplier specs.  I came to the conclusion that the injector
> should be LPS certified and marked as such.  However, most of the 
> injectors I have found by web search do not indicate LPS.
> 
> Does anyone believe that a PoE injector does not require LPS 
certification? 
> If so, why not?
> 
> Regards,
> 
> Don Umbdenstock
> Manager Compliance Engineering
> 
> Tyco Safety Products / Sensormatic
> 6600 Congress Avenue
> Boca Raton, FL 33487 USA
> Phone: 561.912.6440
> djumbdenst...@tycoint.com

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Re: PoE injectors

[emc-p...@ieee.org]

On 3/25/2009, Don Umbdenstock wrote:



I have perused the IEEE 802.3af explanation on various web sites and 
examined
supplier specs.  I came to the conclusion that the injector should be LPS
certified and marked as such.  However, most of the injectors I have found by
web search do not indicate LPS.
Does anyone believe that a PoE injector does not require LPS 
certification? 
If so, why not? 



Hi Don:

I'm not certain what you mean by "LPS certification," but if you meant to ask
if the Ethernet side of the injector should be safety certified as a SELV
circuit, I believe the answer is yes.  For safety analysis per UL 60950 and
other similar versions of IEC 60950, the voltages that appear on an Ethernet
cable are generally considered to be SELV, whether or not the circuit has POE
provisions.




Joe Randolph
Telecom Design Consultant
Randolph Telecom, Inc.
781-721-2848 (USA)
j...@randolph-telecom.com
http://www.randolph-telecom.com  

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RE: PoE injectors

[emc-p...@ieee.org]

Hi Don,

 

Further to what Joe has stated below, according to IEC 60950-1 an ethernet
interface circuit is generally characterized as an SELV circuit, but must also
be considered a TNV-1 circuit if it is subject to overvoltages (atmospheric
conditions). You might also want to read through CENELEC CLC/TR 62102
(replaced ETSI EG 201212) entitled “Electrical safety - Classification of
interfaces for equipment to be connected to information and communications
technology networks” if you haven’t done do already.

 

I don’t believe there is a hard and firm LPS requirement for power supplies
in general nor do I believe that unique LPS certifications are even available.
The LPS qualification is usually formally evaluated as part of formal safety
approval testing to IEC 60950-1 for instance, which is also noted in that
safety report. The LPS marking on the power supply is a result of that.

 

Although with that said, LPS may more likely be more of a customer requirement
rather than regulatory, whereby there should be an adequate selection of LPS
and non-LPS PoE invertors. LPS selection should depend on a customer’s
specific requirements and the specific application. IMHO, for a safer
installation, LPS PoE injectors should be considered.

 

IHTH.

 

I look forward to your reply.

 

Best regards,

 

Ron Pickard

RPQ Consulting

Glendale, AZ 85303

+623.512-3451 tel, +623.848-9033 fax

rpick...@rpqconsulting.com

www.rpqconsulting.com <http://www.rpqconsulting.com/> 

www.linkedin.com/in/RonPickard

 



From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of Joe Randolph
Sent: Wednesday, March 25, 2009 9:20 PM
To: Umbdenstock, Don; emc-p...@ieee.org
Subject: Re: PoE injectors

 

On 3/25/2009, Don Umbdenstock wrote:



I have perused the IEEE 802.3af explanation on various web sites and examined
supplier specs.  I came to the conclusion that the injector should be LPS
certified and marked as such.  However, most of the injectors I have found by
web search do not indicate LPS.
Does anyone believe that a PoE injector does not require LPS certification? 
If so, why not? 


Hi Don:

I'm not certain what you mean by "LPS certification," but if you meant to ask
if the Ethernet side of the injector should be safety certified as a SELV
circuit, I believe the answer is yes.  For safety analysis per UL 60950 and
other similar versions of IEC 60950, the voltages that appear on an Ethernet
cable are generally considered to be SELV, whether or not the circuit has POE
provisions.



Joe Randolph
Telecom Design Consultant
Randolph Telecom, Inc.
781-721-2848 (USA)
j...@randolph-telecom.com
http://www.randolph-telecom.com <http://www.randolph-telecom.com/> 

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RE: PoE injectors

[emc-p...@ieee.org]

I understand that most typical circuits present less than 1k Ohm or upwards of
Meg Ohm load, and that PoE PD circuits are unique in presenting 25k Ohm load. 
Am I correct that once the handshake establishes the 25k Ohm load, that the
PSE continuously monitors the load?  If for example a short develops across
the power line in the PD, would the injector immediately shut off the power to
the PD?

 

Don 
561 912  6440 



From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of
neve...@comcast.net
Sent: Wednesday, March 25, 2009 5:47 PM
To: emc-p...@ieee.org
Subject: Re: PoE injectors

 

Does it matter for the discussion that:

1) Power is not present at the output of the source unless the other side of
the cable connects to a PD (powered device) which "signals" to the sourcing
equipment it is a PD and to turn it on. If you unplug the PD, the power goes
off.

2) The power supply in the sourcing equipment are isolated per IEEE 802.3
(1500Vrms).

?

Neven





From: "Don Umbdenstock" 
To: emc-p...@ieee.org
Sent: Wednesday, March 25, 2009 1:42:50 PM GMT -08:00 US/Canada Pacific
Subject: RE: PoE injectors

Let me share some of my thought process with you.

Hazard based consideration and 60950 would suggest that if a power
source (injector) can provide more than 15W, then a fire enclosure or
other means of fire protection is necessary.  Other means to prevent
fire when a fire enclosure is not provided includes LPS source, product
built with V-1 or better circuit boards, etc.

Most injectors provide more than 15W to be able to power more than one
device and handle line loss.  Thus it would seem intuitive that the PoE
injector (or switch) would be LPS.

What's the rest of the story that I'm missing?

Don
561 912  6440


From: Umbdenstock, Don 
Sent: Wednesday, March 25, 2009 4:34 PM
To: emc-p...@ieee.org
Subject: FW: PoE injectors


Hi Pat,

LPS means "limited power source" per 60950 Clause 2.5; this is the basis
of my question.

Don
561 912  6440

From: pat.law...@slpower.com [mailto:pat.law...@slpower.com] 
Sent: Wednesday, March 25, 2009 12:14 PM
To: Umbdenstock, Don
Cc: emc-p...@ieee.org
Subject: Re: PoE injectors

Hi Don,

What does 'LPS' mean in this context?

Pat Lawler
EMC Engineer
SL Power Electronics Corp.

"Umbdenstock, Don"  wrote on 03/25/2009 
07:23:54 AM:
> I have perused the IEEE 802.3af explanation on various web sites and
> examined supplier specs.  I came to the conclusion that the injector
> should be LPS certified and marked as such.  However, most of the 
> injectors I have found by web search do not indicate LPS.
> 
> Does anyone believe that a PoE injector does not require LPS 
certification? 
> If so, why not?
> 
> Regards,
> 
> Don Umbdenstock
> Manager Compliance Engineering
> 
> Tyco Safety Products / Sensormatic
> 6600 Congress Avenue
> Boca Raton, FL 33487 USA
> Phone: 561.912.6440
> djumbdenst...@tycoint.com

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Re: PoE injectors

[emc-p...@ieee.org]

A primary question in the US is: Does the circuit qualify as a Class 2 (or
Class 3) circuit according to the National Electrical Code? (ref: NFPA 70
clause 725.121) If it fails to qualify, then wiring requirements become quite
stringent.
There are seven possibilities: a listed Class 2 transformer, a listed Class 2
power supply, listed equipment marked to identify the Class 2 output,
thermocouples, limited power circuits of listed equipment meeting chapter 9
requirements, listed information technology equipment limited power circuits,
or batteries with capacity at or below No 6 carbon zinc cells.

To my mind, in this situation, that means the circuit must be both "listed"
and a "limited power circuit".
The decision of determining compliance with the criteria for a limited power
circuit is, to a small extent, left to the listing agency. However, it seems
the limited power circuit designation is an important part of code
requirements.
Providing a circuit which cannot be considered a Class 2 or Class 3 circuit
and must use Class 1 wiring methods will place an immense installation burden
on the user.

Bob Johnson
ITE Safety  

Umbdenstock, Don wrote: 

Dear Colleagues,

I have perused the IEEE 802.3af explanation on various web sites and 
examined
supplier specs.  I came to the conclusion that the injector should be LPS
certified and marked as such.  However, most of the injectors I have found by
web search do not indicate LPS.

Does anyone believe that a PoE injector does not require LPS 
certification? 
If so, why not?

Regards,

Don Umbdenstock
Manager Compliance Engineering

Tyco Safety Products / Sensormatic
6600 Congress Avenue
Boca Raton, FL 33487 USA
Phone: 561.912.6440
djumbdenst...@tycoint.com  





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emc-pstc
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RE: PoE injectors

[emc-p...@ieee.org]

I gave a presentation to the Santa Clara Valley chapter of 
the PSES in JUN2007 that has guidance on this topic.  Find 
it at:

http://www.ewh.ieee.org/r6/scv/pses/ieee_scv_pses_jun07.pdf

(My follow-up presentation from FEB2008 is extraordinarily 
delinquent in being posted, due to s/w issues at my end and 
a full calendar.)

LPS is not sufficient, since the PoE conductors are of 
similar size and use significantly similarly constructed 
modular plugs and jacks.  The maximum current that can be 
dumped into the network is 1.3 A.

UL also has published some Practical Application Guidelines 
on the topic.

Peter Tarver
ptar...@ieee.org

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RE: PoE injectors

[emc-p...@ieee.org]

My apologies for thinking out loud – if a PD can present up to a 13 W load,
then the 25k handshake cannot be part of the load, but rather is restricted to
a handshake circuit.  So the question is whether there is a spec for current
limiting for PSE?  If a PSE is by definition current limited, and AHJs know
this, then LPS or NEC Class 2 marking wouldn’t seem to be necessary. 

 

The reason for the series of PoE comments is to anticipate the needs of the
AHJs.  Is the above conclusion a logical argument for anticipating questions
>from an AHJ?

 

Don 
561 912  6440 



From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of Umbdenstock,
Don
Sent: Thursday, March 26, 2009 8:44 AM
To: neve...@comcast.net; emc-p...@ieee.org
Subject: RE: PoE injectors

 

I understand that most typical circuits present less than 1k Ohm or upwards of
Meg Ohm load, and that PoE PD circuits are unique in presenting 25k Ohm load. 
Am I correct that once the handshake establishes the 25k Ohm load, that the
PSE continuously monitors the load?  If for example a short develops across
the power line in the PD, would the injector immediately shut off the power to
the PD?

 

Don 
561 912  6440 



From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of
neve...@comcast.net
Sent: Wednesday, March 25, 2009 5:47 PM
To: emc-p...@ieee.org
Subject: Re: PoE injectors

 

Does it matter for the discussion that:

1) Power is not present at the output of the source unless the other side of
the cable connects to a PD (powered device) which "signals" to the sourcing
equipment it is a PD and to turn it on. If you unplug the PD, the power goes
off.

2) The power supply in the sourcing equipment are isolated per IEEE 802.3
(1500Vrms).

?

Neven





From: "Don Umbdenstock" 
To: emc-p...@ieee.org
Sent: Wednesday, March 25, 2009 1:42:50 PM GMT -08:00 US/Canada Pacific
Subject: RE: PoE injectors

Let me share some of my thought process with you.

Hazard based consideration and 60950 would suggest that if a power
source (injector) can provide more than 15W, then a fire enclosure or
other means of fire protection is necessary.  Other means to prevent
fire when a fire enclosure is not provided includes LPS source, product
built with V-1 or better circuit boards, etc.

Most injectors provide more than 15W to be able to power more than one
device and handle line loss.  Thus it would seem intuitive that the PoE
injector (or switch) would be LPS.

What's the rest of the story that I'm missing?

Don
561 912  6440


From: Umbdenstock, Don 
Sent: Wednesday, March 25, 2009 4:34 PM
To: emc-p...@ieee.org
Subject: FW: PoE injectors


Hi Pat,

LPS means "limited power source" per 60950 Clause 2.5; this is the basis
of my question.

Don
561 912  6440

From: pat.law...@slpower.com [mailto:pat.law...@slpower.com] 
Sent: Wednesday, March 25, 2009 12:14 PM
To: Umbdenstock, Don
Cc: emc-p...@ieee.org
Subject: Re: PoE injectors

Hi Don,

What does 'LPS' mean in this context?

Pat Lawler
EMC Engineer
SL Power Electronics Corp.

"Umbdenstock, Don"  wrote on 03/25/2009 
07:23:54 AM:
> I have perused the IEEE 802.3af explanation on various web sites and
> examined supplier specs.  I came to the conclusion that the injector
> should be LPS certified and marked as such.  However, most of the 
> injectors I have found by web search do not indicate LPS.
> 
> Does anyone believe that a PoE injector does not require LPS 
certification? 
> If so, why not?
> 
> Regards,
> 
> Don Umbdenstock
> Manager Compliance Engineering
> 
> Tyco Safety Products / Sensormatic
> 6600 Congress Avenue
> Boca Raton, FL 33487 USA
> Phone: 561.912.6440
> djumbdenst...@tycoint.com

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RE: PoE injectors

[emc-p...@ieee.org]

I had a stupid attack.

CHANGE
 Power on TNV wiring to a remote device cannot be considered LPS.

TO
 Power on TNV wiring to a remote device should not necessarily be considered
LPS.

 > -Original Message-
 > From: emc-p...@ieee.org [mailto:emc-p...@ieee.org]On Behalf Of Brian
 > O'Connell
 > Sent: Wednesday, March 25, 2009 10:26 AM
 > To: emc-p...@ieee.org
 > Subject: RE: PoE injectors
 > 
 > Limited Power Source - q.v., 2.5 and 6 of UL60950-1
 > 
 > Power on TNV wiring to a remote device cannot be considered LPS.
 > 
 >  > -Original Message-
 >  > From: emc-p...@ieee.org [mailto:emc-p...@ieee.org]On Behalf Of
 >  > pat.law...@slpower.com
 >  > Sent: Wednesday, March 25, 2009 8:14 AM
 >  > To: Umbdenstock, Don
 >  > Cc: emc-p...@ieee.org
 >  > Subject: Re: PoE injectors
 >  > 
 >  > Hi Don,
 >  > 
 >  > What does 'LPS' mean in this context?
 >  > 
 >  > Pat Lawler
 >  > EMC Engineer
 >  > SL Power Electronics Corp.
 >  > 
 >  > "Umbdenstock, Don"  wrote on 
 > 03/25/2009 
 >  > 07:23:54 AM:
 >  > > I have perused the IEEE 802.3af explanation on various web 
 >  > sites and
 >  > > examined supplier specs.  I came to the conclusion that 
 >  > the injector
 >  > > should be LPS certified and marked as such.  However, 
 > most of the 
 >  > > injectors I have found by web search do not indicate LPS.
 >  > > 
 >  > > Does anyone believe that a PoE injector does not require LPS 
 >  > certification? 
 >  > > If so, why not?
 >  > > 
 >  > > Regards,
 >  > > 
 >  > > Don Umbdenstock
 >  > > Manager Compliance Engineering
 >  > > 
 >  > > Tyco Safety Products / Sensormatic
 >  > > 6600 Congress Avenue
 >  > > Boca Raton, FL 33487 USA
 >  > > Phone: 561.912.6440
 >  > > djumbdenst...@tycoint.com

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RE: PoE injectors

[emc-p...@ieee.org]

Limited Power Source - q.v., 2.5 and 6 of UL60950-1

Power on TNV wiring to a remote device cannot be considered LPS.

 > -Original Message-
 > From: emc-p...@ieee.org [mailto:emc-p...@ieee.org]On Behalf Of
 > pat.law...@slpower.com
 > Sent: Wednesday, March 25, 2009 8:14 AM
 > To: Umbdenstock, Don
 > Cc: emc-p...@ieee.org
 > Subject: Re: PoE injectors
 > 
 > Hi Don,
 > 
 > What does 'LPS' mean in this context?
 > 
 > Pat Lawler
 > EMC Engineer
 > SL Power Electronics Corp.
 > 
 > "Umbdenstock, Don"  wrote on 03/25/2009 
 > 07:23:54 AM:
 > > I have perused the IEEE 802.3af explanation on various web 
 > sites and
 > > examined supplier specs.  I came to the conclusion that 
 > the injector
 > > should be LPS certified and marked as such.  However, most of the 
 > > injectors I have found by web search do not indicate LPS.
 > > 
 > > Does anyone believe that a PoE injector does not require LPS 
 > certification? 
 > > If so, why not?
 > > 
 > > Regards,
 > > 
 > > Don Umbdenstock
 > > Manager Compliance Engineering
 > > 
 > > Tyco Safety Products / Sensormatic
 > > 6600 Congress Avenue
 > > Boca Raton, FL 33487 USA
 > > Phone: 561.912.6440
 > > djumbdenst...@tycoint.com

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Re: PoE injectors

[emc-p...@ieee.org]

Hi Don,

What does 'LPS' mean in this context?

Pat Lawler
EMC Engineer
SL Power Electronics Corp.

"Umbdenstock, Don"  wrote on 03/25/2009 
07:23:54 AM:
> I have perused the IEEE 802.3af explanation on various web sites and
> examined supplier specs.  I came to the conclusion that the injector
> should be LPS certified and marked as such.  However, most of the 
> injectors I have found by web search do not indicate LPS.
> 
> Does anyone believe that a PoE injector does not require LPS 
certification? 
> If so, why not?
> 
> Regards,
> 
> Don Umbdenstock
> Manager Compliance Engineering
> 
> Tyco Safety Products / Sensormatic
> 6600 Congress Avenue
> Boca Raton, FL 33487 USA
> Phone: 561.912.6440
> djumbdenst...@tycoint.com

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