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Subject: Re: TWL: Alternatives to isolation transformer?
From: Arild Jensen (elnav@XXX.XXX)
Date: Mon May 06 2002 - 13:51:17 EDT
Bill Martin wrote
The galvanic isolator blocks small amounts of both AC and DC, but will not block large amounts of
> either. I'm sure Arild understands this, but I didn't want non electronics types to misunderstand.
>
> A galvanic isolator is essentially four diodes wired series parallel so
> that it opens the circuit at potentials less than about 1.3v (ac or
> dc). Conversely, it closes the circuit if there is more than 1.5v or so
> (whether it is ac or dc).
REPLY
Recent changes in the standards for galvanic isolators now require a capacitor to be included.
The old diode only version also disabled the protective function of GFCI's and this was not
considered a good thing. The addition of the capacitor allows the flow of small AC leakage
currents in the milliamp range. This permits the GFCI to function and trip at the 5 ma threshold.
There are additional requirements such as testing for continuity of the green wire in both
directions which will also change the characteristics compared to the old style.
Arild
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