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enter image description hereI have a 12/3 MWBC feeding one single bedroom that is about 8x14 in size. It feeds two lights and approximately 5 outlets. In the panel, each leg was on a 20 amp single pole breaker, one on top of the other. Needing to make some space in the panel (allows 48 circuits), I added some tandem breakers and placed this MWBC on a 15 amp tandem.

Are MWBC permitted on a tandem breaker? If so, does it need a breaker tie? Should I just replace it with two separate single poles breakers (the way it was) and add a breaker tie? Thank you in advance!

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  • @AlK Most likely, you cannot use a tandem for an MWBC. Most tandems end up with each half on the same “leg” of your service (as opposed to opposite legs with a full-size two-pole breaker) meaning you could overload the shared neutral’s limit by a factor of two (30A on 15A wiring, etc). There may exist some single-space breakers that do attach to both poles and would be safe for MWBC use, but they are rare. Post the make of your panel, photos of all its labeling, and the make/model of the breaker you are considering using.
    – nobody
    Jan 11 at 22:38
  • I added the only photos it would allow me to. This is a Homeline 100amp main breaker panel being used as a sub panel. Model of the panel is, HOM2448M100PCVP. The breaker that is being used is, Homeline 2-15 Amp Single-Pole Tandem Circuit Breaker. Considering this line only feeds 2 lights /
    – Al K
    Jan 11 at 23:23
  • 5 outlets, is on a tandem 15amp breaker now, rather than a 20amp and is for a bedroom, do you believe the neutral can still have an issue?
    – Al K
    Jan 11 at 23:29
  • You definitely MUST NOT put a MWBC on that breaker - you risk overloading the (totally unprotected) neutral by a factor of two. If one side is really only lighting you could probably put it on the same breaker as the receptacles and be safe without breaker trips (especially if the lights are LED).
    – nobody
    Jan 12 at 0:08
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    Yes, two separate single-pole 15A breakers handle-tied would be fine. A two-pole 15A breaker would also work (HOM215) for a lower price than two HOM115s and a handle tie, and without the potential hassle of actually locating handle ties.
    – nobody
    Jan 12 at 1:55

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