Shared Neutral, I think...

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  #1  
Old 09-18-04, 08:02 PM
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Shared Neutral, I think...

Question:

I have 12-3 running to a ceiling fan in my bedroom, dedicated with a 20 amp breaker in the panel. I want to add a ceiling fan in another room off the same circuit. I am only using the black and white from the 12-3, leaving the red left at both the box and the panel.

Can I add another 20 amp circuit breaker to the red wire to power an entire additional bedroom with a/c and use the neutral from the first breaker for the second one as well(shared neutral?)

The ceiling fan would still get hooked up to the first circuit(using the black) and I want to explore using the red in a new circuit capacity. Is this correct??
 
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  #2  
Old 09-18-04, 08:14 PM
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It's not a shared neutral as you guess. Both the red wire and the black wire are on the same circuit. They are there to allow the fan and light to be controlled separately. The red wire does not go all the way back to the panel. It probably only goes as far as the wall switch. If there is just one wire of each color in the ceiling box, then the switch in the first room will control the fan in the second room, which is probably not what you want. If there are more than one wire of each color in the ceiling box, then provide more details.

It is very unlikely that this circuit is dedicated to just this one fan. How did you come to that conclusion?
 
  #3  
Old 09-18-04, 08:20 PM
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This was a fresh circuit that I wired myself, so I am certain that it is dedicated. I had 12-3 going to the panel, and only used the black and white on the 20 amp circuit, leaving the red wire floating on both ends, with no breaker at the panel, and no connection in the fan box. I used 12-3 to go from the fan to the switch, but I am only using the black in the box to power the unit. I am POSITIVE that this is the only thing on this circuit.

More specifically, can I add another 20 amp breaker to the red, non-connected wire in the panel, using the same neutral and power additional things in the house in that manner. Are there any rules about a shared neutral which do not apply to standard 2 conductor circuits? My plan is to use the red to feed power to another bedroom and power 5 wall outlets. Thoughts???
 
  #4  
Old 09-18-04, 08:28 PM
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I did not realize that you had wired this circuit yourself, so I was assuming standard practices.

If you understand the dozen or more special restrictions on multiwire circuits, then you can certainly do what you suggest. None of the rules is more important than the rule to make sure that the red and black wires get connected to breakers on opposite legs of the power (not the same as opposite sides of the panel). If you don't ever connect the red and black to the same device, and if you split out the white wire into two separate white wires in the first box you come to (is that the fan?), then most of the other rules are easy. Of course, you might have a big problem meeting the bedroom AFCI requirements, and if you don't know what you're doing, GFCI won't work right.

Don't do this until you study up on multiwire circuits and completely understand the theory of why the neutral doesn't heat up and burn your house down. Also, be sure you understand what happens if the neutral becomes disconnected anywhere. And only do this if you can't afford to simply go out and buy some 12/2 for your new circuit.

If you think I'm trying to make you extra cautious about this, you are right.
 
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