Re: House circuits without Ground wires - GFCIs

["S. Hieber" <shieber at yahoo_com>]

The mysterious m c asked if Terry and I were sure of our
comments about GFCIs:

> You guys sure about this?  My electrition didn't think
> so, but he may have misunderstood the situation.
> 
> > > but this it typical of this house.  It has an
> actual
> > > fuse box.  And it is all 2 wire.  All my things
> are 3
> > > prong.  I buy a lot of adapters.  I can't even
> instal
> > > a GFI because there is no groundwire so there
> wouldn't
> > > be a point.

As Terry pointed out, GFCIs work by detecting ground faults
and they do this by recognizing any difference in the
amount of current between the Hot and Neutral wires.  No
ground wire is necessary for that function.

The idea is that, if the all of the current on one side
isn't going through the other side, then some of it must be
going to ground via some path or other, and hence a ground
fault *must* exist.

If you have two-prong outlets, a very good idea is to
install a GFCI if you want protection from current leaking.

Some older house circuits might have two wires inside a
metal conduit and the metal conduit is attached to ground
at the fuse/breaker box.  In that case, connecting a wire
to the metal socket box housing and tothe ground terminal
on the GFCI socket is a good idea.  But the GFCI will
detect ground faults even if there is no ground connection.
 This is one reason why you can plug in a device that only
has two prongs (for example a standard glass tube aquarium
heater) and if any current leaks (say, the tube cracks and
current goes into the tank, etc.) the GFCI will still trip,
even though no ground wire is involved.
Sam Goldwasser used to have some web pages providing
excellent info on GFCIs.  Those pages seem to be down right
now.  But here is one site with some further info,
including mention of using GFCIs in "ungrounded"
situations.

http://homerepair.about.com/gi/dynamic/offsite.htm?site=http://www.naturalhandyman.com/iip/inf/infxtra/infgfi.shtm

enter all as one line in your browser.


Note that a GFCI will not protect a person from all types
of situations that could expose a person to dangerous
electrical shock, but only from types of ground fault
conditions.

Scott H. 

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