multi-wire light receptable confusion


Old 07-22-01, 10:08 AM
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With a hit-and-miss knowledge of electrical wiring, this is a big mystery. I removed a bathroom light fixture from the wall and undid all the black and white wiring. The wiring consists of 4 sets of black and white wires. I want to install a new fixture. One way I tried that didn't work was to wire all the blacks together and all the whites together. It didn't work. Another way I tried was to wire the blacks from 3 sets together, just capping them off, and the same for the whites from the same 3 sets together, just capping them off. This left one free set of black and white. So, I wired the free set of black and white to the black and white of the new light. It still didn't work. I just read info. about making a white wire "hot." In my situation, was one of the white wires made hot and now I need to find out which one? If I find out which one is "hot," do I then wire it to the black of one set and the black of the new light and will this work then? Somebody PLEASE HELP ME! I can't afford a real electrician! Another problem with this is that somehow this wiring controls some other lights in the same part of the house..........
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Old 07-22-01, 02:43 PM
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what you really need to know is which two wires go to the switch and you can do this with a cheap continuity tester just make sure power is off to the circuit.once you know what two wires go to the switch take the white wire and splice it in with all the blacks execept the black switch wire,now take the black switch wire and splice that in with your black light fixture wire,all other whites get spliced together including your white fixture wire.
Old 07-22-01, 09:04 PM
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Confirm that the switch box has only 1 cable entering that box, if only 1 cable then we know the source of circuit power is at the fixture ceiling box.

3 things that we need to know...

1. Is it only the 1 ceiling fixture that the same switch controls ?

2. which cable is going to the switch ?

3. which cable is the circuit power supply wire ?

Tell me how many cables are entering the ceiling box and how many cable are entering the switch box, each cable should have a black/white/bare wire in it.

1st lets find the circuit power supply wire ,
To find the circuit power supply cable pull the wires out of the box, don't let any wires touch each other or the box.
use a volt meter or use a basic light socket with a known good light bulb in it , temporary connect your volt meter or test socket to the white & black of the same cable, then check the next cable, and so on, (power will have to be to on to check) which ever cable gives a voltage reading or turned on the light bulb, that cable is your power supply cable, MARK IT !

Now the switch cable, a continuity checker testing between the the white and black on the same cable of each of the remaining cables , check with switch on and off, once identified -MARK IT !

Now connect the circuit black to white going to switch , connect black on the switch cable to fixtures black or brass color screw. Connect circuit white to fixture white or silver color screw. Remark the white wire going to siwtch with a piece of black electrical tape at both ends to signify that this is a hot wire.

If there is any other cable connect then black to circuit black, white to circuit white to feed an unswitched cable onward.

The instructions are assuming that circuit power supply is at the ceiling box.

I also just notice that you mentioned bathroom wall fixture, so anywhere I mentioned ceiling box, I mean the location where the light fixture is.

Also remember all bares together and grounded to box (if metallic) and grounding screw or green wire at fixture , it gets connected to ground too.

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