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Old 02-18-2007, 10:19 PM   #1
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2 curcuits in 2-gang switchbox


I have two different curcuits in a 2-gang switchbox. One switch is feeding the light in the dining room. It is a single pole switch. The other curcuit is a 3-way which has the travelers feeding it and the switchleg feeding the light in the kitchen. The neutral to the kitchen light was picked up in this switchbox from the other curcuit. Does anyone know if this is legal according to NEC? My house was built in 99. These two curcuits are on the two different phases and areNOT on a two-pole gang breaker.

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Old 02-18-2007, 11:12 PM   #2
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2 curcuits in 2-gang switchbox


It could be part of a multiwire circuit. That would be OK. If not part of a multiwire then that is not good.

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Old 02-18-2007, 11:37 PM   #3
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2 curcuits in 2-gang switchbox


I do not know what you are refering to exactly. Can you explain what is a multi-wire curcuit.
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Old 02-19-2007, 02:48 AM   #4
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2 curcuits in 2-gang switchbox


Sounds like a multiwire as Joed has already mentioned. In simple terms a multiwire is 2 120 volts circuits from opposite legs sharing a common neutral. this only works if the two hot wires are on different busses in the panel (legs if you will). This arrangement allows return current from the two hot wires to cancel one another in the neutral. In other words if I have 10 amps on one hot wire returning on the neutral and the other hot wire is returning 5 amps then only the difference is flowing in the neutral or 5 amps (10 amps -5 amps). If the 2 hots were on the same leg then the current would be the sum of the return currents. In the above example you would have 10 + 5 or 15 amps flowing in the neutral. So this would be dangerous in that you can easily exceed the amperage rating of the wire. Example: One #12 awg copper hot wire carrying 15 amps the other hot wire (same leg) carrying 15 amps. You would have 30 amps on a 25 amp rated wire. Normally multiwires that havent been split at a junction box are 12/3 g or 14/3 g with red, black and white conductors and bare ground.

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Old 02-19-2007, 09:15 AM   #5
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2 curcuits in 2-gang switchbox


That is what I thought you 2 were talking about. And yes that is what exists, as I stated originally the 2 switches are on the 2 different phases (legs). I verifiied this by the positioning of the breakers in the panel (counting leg-A, leg-B, alternating back-and-forth as most panels alternate the legs to every other 1" space). I also verified this by measuring between the hot feeds for the two switches ( has 240 vac hot-to-hot, 120vac hot-to-neut). I just remember something about this in the 93 NEC stating if this configuration is used, it must be fed from a 2-pole breaker (so there won't be a live wire in the box if you should have one breaker off---this is exactly what I have!) Is this till the case or has this changed?
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Old 02-19-2007, 10:26 AM   #6
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2 curcuits in 2-gang switchbox


I think I found the NEC regulation. Check article 210 (branch curcuits) section 4 (multi-wire branch curcuits) part b----states basically " in a dwelling unit (house--single fam) a m/w branch suplying more than one device on the same yoke shall be provided with a means to simultaneously disconnect all ungrounded conductors at the panelboard where the branch curcuit originated."

Since I have two switches in a two-gang pvc box do i need these on a 2-pole breaker? (also re-read original post!)
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Old 02-20-2007, 12:27 AM   #7
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2 curcuits in 2-gang switchbox


No you do not need the the common trip double pole breaker in your case, though its always a good idea. The Nec only requires the double pole common trip breaker if both hot wires land on the same yoke of a duplex receptacle. You would break the tab between the two brass screws and effectively isolate the top half of the receptacle from the bottom half... the neutral is then shared between the ungrounded hot legs. This is pretty common for supplying a dishwasher and garbage disposal with the receptacle under the sink.

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