multi-wire circuit


Old 09-15-04, 12:52 PM
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multi-wire circuit

I installed a multi-wire circuit last year. At the time, I read several postings at this site on the subject, and have continued to follow this topic. While my project is already finished, I would like to recap it to see if anyone spots any problems, as I could still correct them.

I was concerned that both bathrooms and the master bedroom in my 40-year old home were all on a single 15-amp circuit. So I decided to add circuits to put each bathroom on a separate circuit. I ran a 12-3 romex cable from the panel to the attic, instead of two 12-2's, because the run to attic was difficult and I was concerned about overcrowding in the conduit that encases the cables until they reach the attic. I installed junction boxes in the attic and made splices so that the master bedroom remained on the original circuit and each bathroom runs off one leg of the new multi-wire circuit. Without covering every single detail, I note that:
- The receptacles in the bathrooms are all GFIC.
- I have not pig-tailed the neutral connections because as I understand it, this is not required in my situation since the multi-wire branches are completely separate (i.e., do not run to a single device.)
- I used a 15-amp double-pole breaker for the multi-wire circuit although I later concluded that double pole is not strictly required, for the same reason noted above, namely that the two legs of the multi-wire circuit run to separate bathrooms and at no point are wired to a common device.
- As noted, I ran 12-gauge wire to the attic, on the theory that this would simplify upgrading the bathroom circuits to 20-amp at some time in the future, but I limited the breaker to 15 amps at the present time because there is still some 14-gauge wire in the walls that I did not disturb.

Would appreciate knowing if anyone spots anything faulty in my procedure or logic. Thanks.
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Old 09-15-04, 01:01 PM
Join Date: Sep 2000
Location: United States
Posts: 18,497
I am concerned about your statement, "overcrowding in the conduit that encases the cables." Depending on how many cables that is, you may have a derating problem. Depending on that and the size of the conduit, you likely have a conduit fill problem.

If you split the 12/3 into two 12/2s at the first junction box, most of the concerns about multiwire circuits vanish.

Pigtailing is not required.

A double-pole breaker is not required, but a most excellent idea anyway.

Bathroom receptacles on a 15-amp circuit does not meet current code. A few other bathroom codes may also come into play. However, whether or not your project requires upgrading to current code is a judgement of the inspector. Most inspectors would probably say that it does.
Old 09-15-04, 01:56 PM
Join Date: Jun 2004
Location: Ontario, Canada
Posts: 96
You might also look into installing an Arc Fault Circuit Interrupter breaker (AFCI) on the bedroom circuit. I don't like AFCI, too many false trips, which require a visit to the panel to reset. Although I would think in your case, it's not required, since the circuit would be considered grandfathered? (again, up to the inspector)

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