Shared neutral for just one fixture?

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  #1  
Old 07-20-11, 07:40 AM
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Shared neutral for just one fixture?

I want to see if I can use the existing wiring to set up a fan and fan lights on separate switches.

Here's the situation:

I have two breakers for my downstairs lights. I'll call them A and B. They are on opposite sides of my panel.

Right now, the circuit A hot wire comes into the switch box and runs up to the ceiling box to power the fixture. The neutral for circuit A is present in the ceiling box.

The hot for circuit B is also run down to the switch box. It used to supply power for a fixture removed during a remodel. It continues on to other lights on circuit B. They are just tied together with wire nuts right now.

My question:

Can I use the circuit B hot in the switch box to power the fixture, but still use the neutral from circuit A in the ceiling box where the fixture is? It would be the only thing on circuit B that shared the neutral with circuit A.

Thanks!
 
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  #2  
Old 07-20-11, 07:51 AM
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All conductors of the circuit need to be run together in the same sheath or raceway. If this is a multiwire branch circuit, the same neutral is shared between the two circuits. Are the two hots on the same cable? Is one of the hots red and the other black?
 
  #3  
Old 07-20-11, 08:04 AM
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In the switch box, Romex from A comes down and romex from B comes down as switch runs. So, one wire in each is always hot, and the other is the hot that powers a fixture.

The ceiling box is a junction of hots and neutrals from A. The switch run powered by A in the switch box starts and ends here, too.

I just want to tap into B at the switch box to free up that hot wire from A to use it to as another switch so the light could run separately.
 
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Old 07-20-11, 09:15 AM
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Sounds like you are describing two switch loops. Are the whites and blacks both connected to the switches?
 
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Old 07-20-11, 09:34 AM
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Are the A and B circuit breakers directly across from each other? In any panel that I am familiar with this would mean they are both on the same leg and that a shared neutral may NOT be used. To be certain you would need to measure the voltage between the two circuit breakers. If it is 240 volts then a shared neutral is feasible but if the voltage test is anything other (including zero) then a shared neutral may NOT be used.

Current code requires a two-pole circuit breaker for any shared neutral circuits.
 
  #6  
Old 07-20-11, 09:48 AM
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You may not use the hot from circuit A from the panel out to your new light and the neutral of circuit B from that light back to the panel.

The following has been let to slide by once in awhile on a case by case basis. Use of two 14-2 cables instead of one 14-4 cable. Cable a from ceiling box of circuit A, hot feed down to switch, switched power back to ceiling box for light A. Cable b from same ceiling box of same circuit A, neutral down to same switch box, switched power back to ceiling box and continuing on to another light B.
 
  #7  
Old 07-21-11, 06:35 AM
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Right now, the breakers are directly opposite each other in the panel and the voltage across them reads zero. So, a shared neutral isn't possible right now.

However, it wouldn't be hard to move the breaker for circuit B right beside the one for circuit A and put in a double pole. It's a matter of just swapping circuits with similar loads.

The shared neutral with A would only occur for one ceiling fan/light fixture on circuit B though. I wasn't sure if that made a difference or not. It isn't a true shared neutral between those two circuits. The rest of the lights on circuit B would have their own neutral back to the box and would not be connected to any neutral from circuit A.
 
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Old 07-21-11, 01:45 PM
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However, it wouldn't be hard to move the breaker for circuit B right beside the one for circuit A and put in a double pole. It's a matter of just swapping circuits with similar loads.
It still won't be possible because the conductors arent in the same sheath.
 
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