Electricity is confusing

[Charles Bishop]

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 following.

1. If I turn off the switch all 6 lights go out (as is to be expected)

1. 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.

2. 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)

1. 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 confusing.

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.

[RBM]

You don't have enough information to do more than guess, but it may be possible that there is an emergency backup system connected to these lights, which itself is not working properly

[Joseph Meehan]

You have done a good job of describing what is almost certainly a floating neutral. Some where along the line the white wire is not properly connected or it is missing. If so you have a dangerous situation. I suggest you turn off both breakers involved until you can check it or have it checked. It can cause a fire and damage equipment.

Again ___ Turn off both of those breakers ____ !!!

[Tazz]

is the voltage for the fixtures 120? 277? 240?

are the switches 3 ways? single pole?

need more info...

Commercial buildings usually have the 277 and they usually share the neutrals.

as one poster mentioned there is emeergency lighting that could be involved..

[DerbyDad03]

You might have a shared neutral situation. I have a couple of circuits in my house that share a neutral and the circuits are a pain to work on. I get "bleeding" across circuits when only breaker is on and certain switches are are certain positions.

I discovered this while trying to split up some circuits after I first moved in. I killed the breaker for the circuit I wanted to work on, removed a wire nut in a junction box and went upstairs to make sure the correct outlet was dead. Luckily it was night time because when I went upstairs I saw an overhead light from another circuit glowing slightly. Had it been daytime, I probably would never had noticed it.

Made splitt> I ran across this situation the other day and am confused.

[EXT]

Keep in mind, when you turn off fluorescent lights and have a totally dark room, there is often an after-glow that is visible from the bulbs. This is a natural occurrence to fluorescent bulbs. I used to have a photo darkroom with fluorescent lights, you would have to wait until the glow was fully extinguished before you could open any film boxes or you would fog the film. The fluorescent bulbs were primarily used for cleaning and maintaining equipment and chemical balances, incandescent bulbs were used for "safe-lights".