From: Spehro Pefhany
Subject: Re: Galvanic Isolation Required?
X-Newsreader: Forte Agent 1.92/32.572
Date: Sun, 29 Dec 2002 01:52:12 GMT
NNTP-Posting-Date: Sat, 28 Dec 2002 20:52:12 EST
On Sat, 28 Dec 2002 20:51:09 -0400, the renowned PC
>I'm working on a control unit for diesel generator sets which requires some
>instrumentation to read AC mains voltage from the gen-set. The
>microprocessor board reads the voltage from a conditioning/scaling circuit
>which is then connected to an A/D converter.
>This control board interfaces with the AC mains lines for sensing purposes
>but is also connected to a 12VDC battery which is the starting battery for
>the generator set. The main DC logic supply for the control board is
>derived through the 12VDC battery. Theoretically, the 12VDC could be
>considered "user side" and a shock hazard might exist under just the right
>1. Are there any standards where galvanic isolation would be required in
>this application? I've checked with UL, and apparently they don't require
>it, at least for UL508 (Industrial Controls). How about CE or others?
I'm not aware of any, but you might have to (proably should)
mechanically interlock access to the battery, which could cost more
than the isolation. You might try sci.engr.compliance for a more
reliable answer on this.
>2. Despite standards, can there be a case made that the potential liability
>of a shock hazard is very real and therefore advisable to include galvanic
Yes. It's probably fairly inexpensive, it could possibly protect the
electronics under some conditions. If your system will be made in
volume there are inexpensive and very accurate PTs that could do
OTOH, if you add some isolation, and there is access to the battery,
then you'd better make sure that the isolation you add is good enough
to meet all the applicable standards.
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