Re: GFCI
| Subject: | Re: GFCI |
| From: | Martin Tom Brown |
| Date: | Thu Apr 25 15:03:33 1996 |
> In a message dated 96-04-24 18:11:24 EDT, you write:
>
> >Thanks for your info. I can only imagine what a GFCI really is; my image
> >was an ammeter on both legs of the circuit:
> >
> > -----(A)-----
> > line load
> > -----(A)-----
> >
> >and the thing tripped if the ammeter outputs differed by more than an mA
> >(which means that the mA is sneaking off somewhere where it shouldnt).
> >If thats true, why would the "GFCI have to be grounded to earth?".
Out of curiosity what does GFCI stand for?
In the UK they are called ELCB (earth leakage circuit breakers),
and are good value in wet grass with UK mains at 240v and 50Hz.
I can attest to how unpleasant mains applied to the eyepiece
can be from when we had a motor fault on an observatory scope.
> Hmmmm....... after I thought about it a bit, I think you may be right. I
> have never actually looked at the design of a GFCI, so I am not sure, but I
> guess it really is a current comparator, looking at the two sides of the AC
> line. That function would not have to be ground referenced.
Although the test is for current balance on live and neutral many
ELCBs refuse to supply any power at all unless the earth is OK.
Instead a neon lights saying line fault to show the earth is NBG.
(this may not be true of all ELCBs or US two pin systems)
Regards,
-- Martin Brown <martin@nezumi.demon.co.uk> __ CIS: 71651,470 Scientific Software Consultancy /^,,)__/
