Hi folks
I have not been following all this thread, but I have the following
comments:
I have substantial reservations about Jim's first comment:- to put the
external protective earth on as the first item on the stud. This is likely
to cause a particular problem if the supply cable has to be replaced due to
damage etc., as you will have to remove/replace all the connected internal
earthing wires to do it!
I believe that you should always use at least TWO studs/terminals for this
type of thing, and dedicate one solely to the earth of the external supply
connection. Then the whole issue becomes much simpler in both theory and
practice - both for the manufacturer and the installation/service engineer.
The above may not be mandated by most standards but I believe it is both
common sense and good practice.
As regards UL's comment on the need to put the circle on the earth symbol
on external earth terminal - I think they were VERY wrong unless that was
the terminal for connection of the PRIMARY MEANS of earthing (which it
rarely is) !
The whole idea of the circle is to designate the terminal for that purpose
ALONE; using it anywhere else is going to re-introduce the confusion that
the circle was designed to eliminate, as stated in (for example) the first
two sentences of IEC/EN 60950 Clause 1.7.7.1:
"The wiring terminal intended for connection of the protective earthing
conductor associated with the supply wiring shall be indicated by the
symbol .... (IEC 417 No. 5019). This symbol shall not be used for other
earthing terminals"
Regards
John Allen.
Racal Defence Electronics Ltd.
John Allen
----------
From: Andrews, Kurt[SMTP:kandr...@tracewell.com]
Sent: 18 January 2000 15:26
To: jim_bac...@mail.monarch.com; Jackson; William;
'emc-p...@majordomo.ieee.org'
Subject: RE: Proper Protective Earth Ground Symbol
Jim,
For the Protective Earth Terminal, that is the ground from the power cord
or
IEC Inlet that should be located just inside the equipment needs to be IEC
417, No. 5019, the circle upside down tree. Also the incoming ground MUST
be
the first on a stud and secured by its own lockwasher and nut. You may then
stack other grounds to other parts of the equipment on top of this ground.
You may use a separate lockwasher and nut for each additional ground or one
for all of the additional grounds. There may also be other ground studs in
the unit if you don't want to run wires to the Protective Earth Terminal.
This assumes an all metal construction, which is what we use. We have used
both the upside down tree symbol, IEC 417 No. 5017, and the
Equipotentiality
symbol, IEC 417 No. 5021 for these additional grounds with no problems. For
an additional ground on the outside of the equipment we have used the same
symbol as for the Protective Earth Terminal. When we sent a unit in once
for
safety testing to UL we had the upside down tree without the circle next to
an outside ground terminal and they told us it has to be the one with the
circle around it. I would think that the frame ground symbol, IEC 417 No.
5020 (pitchfork) would also be acceptable although we haven't used it.
Hope this helps,
Kurt Andrews
Compliance Engineer
Tracewell Systems, Inc.
567 Enterprise Dr.
Westerville, OH 43081
Ph. 614-846-6175
Fax 614-846-7791
Email: kandr...@tracewell.com
-----Original Message-----
From: jim_bac...@mail.monarch.com
[SMTP:jim_bac...@mail.monarch.com]
Sent: Tuesday, January 18, 2000 8:18 AM
To: Jackson; William; 'emc-p...@majordomo.ieee.org'
Subject: Re:Proper Protective Earth Ground Symbol
forwarded for William.... Jim
____________________Reply Separator____________________
Subject: Proper Protective Earth Ground Symbol
Author: "Jackson; William" <wjack...@harris.com>
Date: 01/14/00 4:59 PM
Greetings all,
I have a request for interpretation of requirement. Which symbol is
correct
for use on a chassis for protective earthing - the upside down tree
or the
circle upside down tree or the pitchfork?? (Note:- the ground on
the back
of the box is generally marked "GND" and is screw and locking washer
configuration). What is the correct marking to satisfy a NRTL for a
marking?
Thanks,
Bill
Bill Jackson, CQE
QA Prgms&Eng/Product Safety
Harris
RF Communications Division (RCD)
(716)-242-3897
wjack...@harris.com
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