GFCI measure the current in the active and the current in
the neutral. If the two currents are the same the GFCI does
not trip. If the neutral is connected to another active not the
one coming from the GFCI then the current in the neutral
coming from the GFCI will be different than the active coming
from the GFCI and the GFCI will register a ground fault and
not reset. This is called crossed neutrals.
The Active and neutral going to the GFCI is the same as that in
the House circuits and can be used to supply lights or anything
else. But the Active and neutrals leaving the GFCI can only be
used with each other and cannot be connected to other actives
or neutrals otherwise the GFCI will trip and refuse to reset.
As an example a GFCI has a active and neutral connected to a
power outlet. Then somebody splices into the neutral and runs
it to a light with a different active as soon as the light is turned
on the GFCI Trips


"Donna" wrote in message
...
On Mon, 26 May 2008 23:22:46 -0700, Donna wrote:

Can you tell how this bathroom light-switch circuit is wired based on
these
15 highly annotated photos?
http://www.flickr.com/photos/2702997...74838278/show/

This question is a followup to a previous question on the same topic.
All the circuit breakers operate something (although some have tons of
circuits on them and others have almost none).

Wiring isn't as easy as it looks!
Can you help me figure out how to hook a simple light switch in this
bathroom?

Here is the wiring table (see the well annotated photographs)
The wiring table is as follows (parenthesis are when I turn on the
adjacent
bathroom light switch which causes the voltage to change for some strange
reason in the first bathroom).
-----
left-most white to ground = 0 volts (0 volts with the adjacent switch on)
right-most white to ground = 26 volts (117 volts with adjacent switch on)
black to ground is 119 volts (118 volts with the adjacent switch on)
red to ground is 119 volts (117 volts with the adjacent switch turned on)
-----
left-most white to red is 26 volts (117 volts with the adjacent switch on)
right-most white to red is 0 volts (15 volts with the adjacent switch on)
black to red is 83 volts (0 volts with the adjacent bathroom switch on)
-----
white to white is 26 volts (117 volts with the adjacent switch turned on)
black to left-most white is 118 volts (118 volts with adjacent switch on)
black to right-most white is 83 volts (0 volts with adjacent switch on)
-----

Can you give me an idea of why the voltage changes when the adjacent
bathroom light switch is turned on with bulbs in the sockets of this
adjacent bathroom light switch (which is a two-wire switch in this
adjacent
bathroom)?