Hello EMC-PSTC Community,
I forwarded Kris Carpentier's questions on clause 6.4.1 of IEC 950 to
the Convenor of the responsible WG7 of TC74, Mr. Helmut Hintz. Since he
is not subscribed to this forum, here is his reply:
Hallo Kris,
here are my answers to your questions.
1) Separation between TNV-1 & 3 circuits from earthed parts:
- permanent earth:
test is not required:
- earth connection via plug (type A or B):
test is required. Reason: if the plug is diconnected,
no earth is available and the transient passes on the
accessible part.
2.) Separation between TNV-1 & 3 circuits and other circuits
- in general:
test is required
- in the special case, e.g. the circuit is far away and
between TNV and SELV are a lot of permanent earthed other
circuits, a test according to 6.4 is not necessary,
provided that a carefully made investigation of all circuitries
shows, that the transient can not pass on to the SELV circuit
via the permanent earthed other ciurcuits.
3.) Permanently earthed or earthed via a plug:
yes, there is a difference.
- only between permanently earthed parts no test is required.
- for plugable equipment type A or B a test is required.
- for plugable equipment type A or B and the equipment has in
addition a permanent earth connection a test is not required.
Assumption: Permanent connection is always made by service personnel
best regards
helmut hintz
--
Kind regards/mit freundlichen Gruessen,
Horst Dierich, Germany
EMAIL: [email protected]
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Dear collegues,
I have a question about clause 6.4.1 of IEC950/A1/A2/A3/A4.
This clause deals with protection of operators against
lightning coming on TNV-1 or TNV-3 lines.
In paragraph b), it is required that a pulse test must be made
between TNV-1 or -3 and "parts that can be touched by the testfinger".
I assume that an enclosure made of metal, and that contains these
circuits, is a "part that can be touched".
Further-on, this clause mentions that "these requirements do not apply
where it is shown that safety is provided by other means, for example
between circuits each of which has a permanent connection to earth".
My assumption:
>From my point of view, I assume that the lightning is supposed
to enter the system in common mode.
My question:
If the above assumption is correct, is it allowed not to perform
this test if the metal enclosure is earthed in case of:
- a permanent earth connection made by service personnel?
- a connection made with a plug like Pluggable equipment type A?
The same clause, par. c) deals with isolation between TNV-1 or -3 and
"circuitry that is provided for connection to other equipment".
If this interface circuit (SELV in my case) is electrically
"far away" from TNV-1 or -3, which means that a lot of electrical
ground connected to PE is between both of them, is it then not
possible not to perform this test? I'm still convinced that a real
lightning pulse is looking for a solid ground (PE) as a return path
and not an SELV interface. Is there a difference regarding the way
the grounds (PE) are connected, permanent or pluggable ?
When, during the pulse-test, there is a spark-over from TNV-3(1) to
PE, is this allowed?
Kind regards and really looking forward to Your opinion!
Carpentier Kris
Alcatel Telecom
Fr. Wellesplein
B-2018 Antwerp - Belgium
tel.: 32 3 240 7986
fax.: 32 3 240 9933
email: [email protected]
ref:kcarpentier/[email protected]
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