Dear Ray,
Regarding the Nordic variation to EN 60950 - It may seem an obvious
question, but if you are testing to EN 61010, then why are you
concerned about a Nordic variation to EN 60950 ? Further, dealing
with the Nordic deviation, the usual connotation of "insulation" does
not include earthed conductive (metal) cases. The bridging of
insulation would imply something like a varistor from the primary to
the secondary of a transformer. There are other examples, but IMHO
placing a varistor from L-G would not violate the letter or the
intent
of the Nordic deviation.
Best regards,
Dan Teninty PE
HMSC
Tucson, AZ
[email protected]
______________________________ Reply Separator _________________________________
Subject: Surge Suppressers
Author: [email protected] at CCGATE
List-Post: [email protected]
Date: 5/13/97 9:49 AM
Dear Friends,
It seems that surge suppressers have been a topic of much discussion
lately. Must be all of the surge testing to EN61000 4-5! Well at least
that's what brought up our issue.
We have a piece of 230V equipment that failed the surge test, (safety
testing will be to EN61010). In reviewing how to install varistors, we
have run into some concerns. In Europe the 230V supply is 1 line, 1
neutral, and 1 ground wire. A varistor connected between line and
neutral will suppress a surge, as long as the neutral is grounded.
For the 230V US voltage, there is 2 hot lines and a ground. To make
the varistor effective, it seems that the varistor needs to be
connected to ground.
However, I know of a Nordic deviation out of EN60950 that states:
(DK, FI, NO, SE). Transient protection components shall be installed
in such a way that insulation for protection against electric shock
will not be bridged. This means that transient protection components
must not be connected to protective earthed parts in pluggable
equipment or to other accessible parts.
I think the concern here is the possibility of not having a good
ground, and then if the over voltage is shunted to ground, the chassis
could become hot.
Is this a valid concern? It sounds like a "double fault" scenario to
me. If so, does anyone have an alternative solution?
Thank you for your consideration.
Happy is the man that finds wisdom and gets understanding!
Ray Russell
[email protected]
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