|
|
|
|
|||||
|
||||||
Subject: Re: TWL: Alternatives to isolation transformer?
From: Bill Martin (Martin_WJ@XXX.XXX)
Date: Fri May 03 2002 - 12:54:53 EDT
>A galvanic isolator only breaks the DC path in the green wire. By design
>it has to allow AC current to flow and therefore is not a preventative for
>stray AC leakage current problems.
This is not true, though a common misstatement. 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).
Since the normal galvanic potentials are less than 1v, the normal galvanic
currents are blocked. If there's a failure in your appliances though that
tries to put 115v on the ground, then the isolator quickly conducts that
current to provide safety. This is where the misconception comes from that
it blocks DC but not AC. It actually blocks low potentials, but not high ones.
Bill Martin
Telegraph Hill
|