"Sbharris[atsign]ix.netcom.com" wrote in
ups.com:

an RCD/GFI, which
places a small voltage between neutral and ground as they exit the RCD
device. After all, the ground and neutral are connected together in the
service panel, so there's no difference between them unless the RCD,
connected after the panel, puts it there.

You are so wrong!!!!!

The purpose of this small
voltage is so the RCD can detect a ground-neutral "fault" (one where
the neural wire has touched the gound inside your lamp or other
appliance) and trip when that happens. The reason RCDs do this is
because having the neutral touch ground makes the major feature of the
RCD (the ability to tell if more current is flowing in the hot wire
than in the neutral, signaling an extra path to ground which may be you
being electrocuted) inoperative. So the RCD is designed to shut off the
power if its sensing function (which requires a separate neutral and
ground path as they exit the device) is compromised and it becomes
"blind" and unable to perform its function. But again, if you don't
have an RCD in the first place, none of this applies. YOU don't care if
the ground touches neural in your old lamp UNLESS you have an RCD/GFI
to trip in the first place.


The GFI does not work that way. The ones I have seen use a small toroidial
transformer to sample the current flow in the hot and neutral lines. (Some
also sample the safety ground and trip if there is any flow there).

The circuit is a balanced bridge as long and the current in the hot line is
equal to the current in the neutral line, the GFI does not trip.

If there is an imbalance, it implies that some current is flowing through
something OTHER than the designed load and that current is going to a
different neutral or to earth ground.

You can still get electrocuted if you have one lamp that has the hot
shorted to the frame and you touch that and another device that has neutral
connected to the frame. If both were on the same GFI protected circuit, you
would NOT trip the GFI.

NEVER connect the neutral to the frame of any device because you defeat the
GFI when you do this. Frame always connects to safety ground.

Your advices would also make the device deadly if it is ever used in an
older house with two wire plugs and someone plugs it in backwards.

Never connect neutral to the frame.

--
bz

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

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