I ran across this situation the other day and am confused.
There are two rooms in a commercial building. The larger room has 4
fluorescent fixtures in the ceiling. The second, smaller room has two. The
smaller room has a switch to turn on it's lights. However this is fed from
the larger room switch (first switch) and the small room switch (2nd
switch) only works if the first one is on.
So, I'm testing the power on the first switch to see which is power and
which is the switch leg, and accidently short out the switch and trip the
breaker. "Great" I think, at least I know which breaker controls the
lights. Sure enough, it's labeled "Lights" in the breaker box.
However, yesterday when I wanted to change out the switch. I noticed the
1. If I turn off the switch all 6 lights go out (as is to be expected)
2. If the switch is on, and I turn off the breaker, the fluroescent bulbs
show a "glow" as if the power is on but reduced.
3. If the breaker is off and the switch is on, I measure about 85V at the
power side and switch leg of the switch. The lights have a "glow" as
above. (I think this diminishes with time and the lights finally go out)
4. If the breaker is on and the switch is off, I measure 135V at the power
side of the switch.
What I discovered is that there is a second breaker, labeled (Lights and
Heater (baseboard electric heater in the large room). If I turn this off
as well as the first one, there is no longer any power to the switch.
The wiring is a rat's nest of boxes and red wires to and from the switch
and fixtures (along with additional wires from other lights and outlets)
so it would be time consuming to trace where the wires come from and go.
It's commercial so I'm assuming that it was done to code, it's just
I didn't check, but assumed that the fixtures were 120V rather than 240V.
Actually, I did notice that some only had one power wire going into them
so it's safe to assume that they're 120V.
Any suggestions as to what might be happening? I took out the switch
already, but will be back on Monday and can get additional info (assuming
this doesn't mean tracing wiring) then if you need it.