Two circuits from one cable and lights in "series"


Old 05-12-04, 01:39 PM
Jeff Stock
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Two circuits from one cable and lights in "series"

Now that I've got my old wiring taken care of in my bathroom remodel, I'm ready to go at the new wiring. I've seen so much helpful advice here that I thought I offer up a couple of questions/scenarios for suggestions.

1. I have to pull two new 20A circuits -- one for bathroom GFCI receptacles and one for electric radiant heat in the floor. I've had one suggestion to just pull one 12-3 cable from the breaker box and split the circuits in a junction box, thereby pulling 1 cable instead of 2. This advice came from the inspector at the city planning dept, so I'm guessing it's ok per code in the city. Should I follow this advice? If I do, which color wire becomes the common wire? Would there be any difficulties hooking this up at the breaker box? (I would be using a double breaker in the box.)

2. I actually have to pull a total of 3 new circuits, because the bathroom lights need their own 15A circuit. I was planning on pulling a 12-2 cable for this new circuit. The lighting circuit will control 6 recessed lighting fixtures. I have read (on other online forums) the repeated suggestion that I run a wire from the switch box to a 4" junction box and then fan out cable from this junction box to each fixture. The reasoning behind this would be that if one light needs working on, it could be disconnected and worked on and the others would still function. I don't see much benefit to this, because I feel better about an entire circuit being dead at the breaker box when I work on it, just in case... Are there any other benefits to wiring the recessed lights in this fan out fashion? If I choose to wire the lights in a physical series, would I pigtail together in a wirenut at each light: black from switch/prev + black to next + black to this and white from switch/prev + white to next + white to light?

Thanks again for all the help
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Old 05-12-04, 02:23 PM
Join Date: Jan 2002
Location: Chicago
Posts: 1,915
Usually a single 20A circuit is enough to feed the whole bathroom, but with that many lights running 2 would not be a bad idea. I would run a 12-3 and a 12-2 circuit (both with ground of course). Split the 12-3 (one red, one black (both hots) and one white (neutral) so that the red and white will feed the heater, and the black and white will feed the lights. Feed the GCFI outlets in the bathroom from the 12-2.
I don't think you have to GCFI protect the radiant heat.
Old 05-12-04, 02:31 PM
Jeff Stock
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Thanks for your advice.

Originally Posted by trinitro
I don't think you have to GCFI protect the radiant heat.
This radiant heat manufacturer (WarmlyYours) requires GCFI protection, either in the thermostat, at the circuit breaker or at the line's end near the control device. The thermostat they sold me has GCFI protection built in, so I'm ok there.

Thanks again
Old 05-12-04, 02:50 PM
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
You can certainly run a separate circuit for bathroom lights, but I'm not sure you need to. I suppose it depends on what else is involved.

Feeding bathroom receptacle outlets and feeding the lighting in the bathroom is allowed by code, as long as that same circuit does not feed anything outside the bathroom. Is a fan involved? What size bulbs do you plan to put in the recessed lights? 20 amps is a lot of current. Unless you are talking about a powerful hairdryer, or a powerful curling iron you may be okay. However, if you do run a separate circuit for the lights then you can use that circuit elsewhere if you need it.

Running 12/3 and feeding two circuits is called a multiwire circuit. The white wire is the neutral. Neutral wires are always white. Nothing else can be used for neutral wires. (In the US anyway.) If you do run a multiwire circuit, remember that all neutral connections that enter and leave an outlet (receptacle, light, whatever) must be pigtailed. You cannot run the neutral through a device.

As for the idea of a common junction box which branches out and feed the lights, I disagree. The first problem with this is that the junction box must be permanently accessible. This is easy if an attic is above the bath, but if there is no attic above then you end up with a box that has a blank cover somewhere you can see it, and access it. I would run to the first light and then on to the second, then to the third, etc.
Old 05-12-04, 03:29 PM
Jeff Stock
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I was planning on running 60W or 75W bulbs in the lights. I forgot about the ceiling fan -- it will also be on the lights circuit. It's just a fan, no lamp.

I like the idea of a new circuit for the lights because the rest of the lights in the 2-story house are all on one circuit, and adding more to that circuit would definitely put me over the wattage limit for that 15A circuit.

I agree with you about the fan-out box. Even though I've got an attic, I'm sure not going to climb up there just to disconnect one light so I can work on it while the others are running.


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