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Old 10-24-2010, 01:58 PM   #1
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Two circuits in one ceiling junction box?


Hello,

I am trying to install an overhead light fixture in a house that I bought with some partially finished rehab work.

There is a ceiling junction box in one room with two sets of wires, each on a different breaker. One group has two white wires, one red, one black. The other has only one white and one black. The wall switch has one white and one black wire. I tried using just the one white and black group and the light did not come on. I would be very grateful for any advice!

Thanks!

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Old 10-27-2010, 11:26 AM   #2
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Two circuits in one ceiling junction box?


Hello,

I am trying to install an overhead light fixture in a house that I bought with some partially finished rehab work.

There is a ceiling junction box in one room with two sets of wires, each on a different breaker. One group has two white wires, one red, one black. The other has only one white and one black. The wall switch has one white and one black wire. I tried using just the one white and black group and the light did not come on.

First, I would like to know if this is dangerous. If not, I would be very happy for any suggestions about wiring this light.

Thanks!

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Old 10-27-2010, 12:23 PM   #3
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Two circuits in one ceiling junction box?


TRhere is no problem running two circuits to the same junction box provided there is enough space in the box and you do not combine neutrals from one circuit with neutrals from the other circuit there.

If the light did not come on when you hooked up the black and white wires in the small group (one cable?) are you sure it is a different circuit as opposed to a cable going down to the switch and nowhere else?

When you figure out that one cable goes down to the switch only then you connect the black wire of that cable to the light fixture black, the other wire of that cable to the live power wire (red or black), and the white of the fixture to the neutral (white) that accompanies the live power wire.
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Four inch round (octagonal) metal boxes 2 inches deep are usually too small for handling two circuits from the panel. You can buy a full width (4 inch) ring that fits over the open box front giving you another 1-1/2 inches of depth.
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Last edited by AllanJ; 10-27-2010 at 12:29 PM.
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Old 10-27-2010, 01:04 PM   #4
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Two circuits in one ceiling junction box?


Before much help can be given you will need to determine the function of each wire. The OP states Chicago as a location so they could be dealing with conduit not cables, but this should have changed the wire colors.

How did you determine that two circuits were involved? Did you consider that this could be power in and power out and a switched hot?
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Old 10-31-2010, 11:33 AM   #5
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Two circuits in one ceiling junction box?


If you have only a white and black at the switch, it is usually because it is fed hot by a piece of 2-wire BX cable. One wire is the hot and the other is the switchleg that should be connected to the load, or hot lead on the fixture. I would need to know what wires in the junction box are spliced together to figure out what to do next but if I had to guess without seeing a picture this is what I would expect to see: You have 3 seperate pipes/conduits/cables entering the junction box, all have a hot and neutral except for the cable going to the switch. The red and 2 blacks should go together. The white from the switch should go to the fixtures' black lead. The other 2 whites should splice with the white lead to the fixture. If this all sounds like what you have, you may want to wire it this way. (make sure the power is off first.) If you want check out my website for my phone # and I can walk you through it.
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