Thanks Allen,
I would agree with the pluggable A and B issue. Because of the
concern with the leakage I indeed read this section as I knew there was some
sort of exception. In reading it, I'm out of the office and doing this from
very recent memory, the information you present is correct. This buy the way
was the UL60950 standard, so as up to date as I can get.
The issue of the ground pin is very interesting, I wasn't aware of
what the real concern was between these two types. So now another question.
If this equipment has a chassis bonding connection like you find in
telephone line up equipment, would then it fall under the class B pluggable.
I can still remove power cords, but have a chassis to frame bonding wire in
parallel to that. (Yes, I know most of that stuff is DC but there is a small
number that is not). I hope to work with the power supply folks to reduce
the problem through filter design if I can, but I think this is an
interesting questions. What do you think?
Gary
-----Original Message-----
From: Allen, John [mailto:[email protected]]
Sent: Friday, January 19, 2001 12:41 AM
To: 'David Gelfand'; EMC-PSTC (E-mail)
Subject: RE: Looking at leakage current specs
Hi folks
I (and I believe, a number of other people) disagree with the last sentence
of David's message - in so far as it is NOT merely a question of having a
longer grounding pin.
IEC and EN60950 - and I think also the common UL/CSA standard (but not
having seen the latest edition) - allow high leakage equipment to be
connected by a mains plug ONLY if it can be classified as "Pluggable Type
B", and NOT "Pluggable Type A".
If you then refer to the definitions of these two types of equipment (in
those standards) you will see that Pluggable Type A" uses a domestic
grounding plug, whilst "Pluggable Type B" uses an industrial plug , e.g.
IEC/EN60309 (but I would also personally class many of the North American
NEMA 6P-XX "Twistlock" plugs as being in this category).
The significant point about the latter types of plugs is that they have some
mechanism to positively lock the plug into the socket and thus ensure the
grounding continuity - whereas domestic plugs generally do not and can
"rock" badly in the socket - thus compromising the grounding of the
equipment.
There are also minimum conductor size requirements for the grounding
conductor, and an overall 5% limit on the leakage current (although I doubt
that this will affect much pluggable equipment!!)
John Allen
THALES Defence Ltd,
Bracknell, UK
-----Original Message-----
From: David Gelfand [ mailto:[email protected]
<mailto:[email protected]> ]
Sent: 18 January 2001 21:30
To: EMC-PSTC (E-mail)
Subject: Re: Looking at leakage current specs
Gary,
The measurement is made with all power supplies in parallel, but
you can exceed the 3.5 mA limit if you provide a warning to ground equipment
before connecting. With standard power cords this is done by having the
ground
pin slightly longer than the line and neutral.
David
David Gelfand
Regulatory Approvals
Memotec Communications Inc.
Montreal Canada
----- Original Message -----
From: "Gary McInturff" <[email protected]>
To: "EMC-PSTC (E-mail)" <[email protected]>
Sent: Thursday, January 18, 2001 10:44 AM
Subject: Looking at leakage current specs
Was reviewing a number of power supply specifications and would like
to parallel a couple, but the leakage/touch current on them is in the 2 mA
range. Isn't most of the leakage current produced (produced might not be the
word I want) in the upfront filter caps - W and Y capacitors and such? If I
parallel these aren't I likely to see a significant increase in the leakage
current, and probably blow by the 3.5 mm requirement for ITE?
Would the measurement be made twice, once for each supply or would I
have to provide a common input to both supplies and then measure between
chassis and this common point's protective earth terminal?
Gary
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