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From: Spehro Pefhany
Subject: Re: UL Leakage Current Test - disconnecting Y-capacitors?
X-Newsreader: Forte Agent 1.92/32.572
Date: Thu, 16 Jan 2003 15:06:03 GMT
NNTP-Posting-Date: Thu, 16 Jan 2003 10:06:03 EST
On 16 Jan 2003 06:40:12 -0800, the renowned email@example.com
(Klaus Kragelund) wrote:
>I'm performing an UL leakage-current test. The test is conducted by
>removing the ground wire and connecting a amp-meter from the chassis
>(instrument ground) to either mains wire.
>This is fine - but what puzzles me is that our Q department says it is
>ok to remove any Y capacitors during that test. Anybody know the
>rationale behind that?
Probably because the reactance of the capacitors is known and
constant, and their leakage is low (they are subject to rigorous
testing and have high enough breakdown voltage that things will
probably arc elsewhere before the capacitor fails), so you can
calculate that current seperately. The reactance might mask more
serious leakage that might not be so well behaved.
Y capacitors are typically thouands of pF.
>If I were to build an instrument with many
>Y-capacitors in parallel the current drawn by these will be high and
>possible lethal if the ground wire was removed....
Probably a good idea not to do that.
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