Can 12-3 wiring be used for two seperate circuits?


Old 08-08-05, 06:15 AM
Jerry Hartman
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Exclamation Can 12-3 wiring be used for two seperate circuits?

Can you use a 12-3 line to connect two seperate circuits (one bedroom, one family room)? My friend told me that you can use the black for one circuit and the red for the other - sharing the neutral. - using single pole breakers

Another friend told me that the breaker would have to be a 2-pole b\c of the single neutral - Using this setup would then turn off both rooms when servicing.
Which is the way to go?
Thanks for the help!
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Old 08-08-05, 06:28 AM
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Using 12-3 for two 120 volt circuits creates what is called a multi-wire circuit. Technically this is not two circuits, but rather one circuit which acts like two.

There are special rules that apply to multi wire circuits. The two hot wires MUST be connected to opposite halves of the incoming 240 volts. This ensures that the neutral current will never exceed the circuit breaker value. It is true in certain circumstances that the two circuit breakers can be single breakers, however for safety and t make it harder to incorrectly place the breakers, a 240 volt breaker (or two 120 volt breakers tied together) is recommended. Code dictates that whenever a common device is used for both portions of the circuit (such as one duplex receptacle having both halves of the circuit) that the single or tied breakers are required. Another important rule is that the common neutral cannot feed through a device, rather it MUST be pigtailed.

Most of us here do not recommend multi wire circuits in residences except for very specific situations. This is probably not one of them.

There is something in your post which may prohibit this anyway. A bedroom circuit requires AFCI protection. You need an AFCI breaker for this. This will complicate the picture.

My advice is to forget about a multi wire circuit in this case.
Old 08-08-05, 06:58 AM
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I would also suggest that you forget this idea, unless perhaps 12/3 is free to you and 12/2 is very expensive. There just aren't enough advantages to justify the disadvantages. Having said that, there's nothing wrong with multiwire circuits when done by someone very experienced with wiring and who thoroughly understands the electrical principles involved and all the special rules and hazards. They have their place, but it's a narrow niche.
Old 08-09-05, 11:16 AM
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Wire is cheap.......... safety/security/peace of mind - Priceless!

Last edited by thezster; 08-09-05 at 11:16 AM. Reason: lousy spelling
Old 08-09-05, 02:10 PM
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Received 0 Votes on 0 Posts that takes me back a few years as I can only remember the last time anyone in my company used a Multi-Wire circuit with 12/3 was when they added a Dishwasher and a Disposal to a house and ran the 12/3 to the sink area junction box and put a recept in the 4 x4 for the dishwasher and then feed the disposal direct from the junction box.

Used the 12/3 Multi-Wire circuit to run both that was some time ago and heck most just do not mess with those anymore....with all the Non-Linear and Linear issues of today it is just not worth it.

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