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Questions tagged [mwbc]

Use this tag for questions about Multi-Wire Branch Circuits, sometimes called "Edison circuits".

A multi-wire branch circuit is used to conserve wire in North American wiring when dual (line to line and line to ground) utilization voltages are present, such as in the 120/240V split-phase system used in residences or Wye type three phase systems (120/208Y, 277/480Y) found in commercial work.

These require a common disconnecting means (either a pullout disconnect with multiple fuses, multiple single pole breakers linked by handle ties, or a multi-pole breaker), and the neutral must be pigtailed to wiring devices so that removing a device does not unlink the neutral. They are most commonly used for kitchen receptacles (small appliance branch circuits), despite having compatibility issues with and most protection, but may be used for other things as well.

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What is a tandem breaker (aka duplex, cheater, twin, double-stuff, etc.)?

I keep hearing about tandem breakers, and how they won't work with 240V loads and how they should never be used for a multi-wire branch circuit. Aside from those issues... What is a tandem breaker? (note: they can be thrown independently).
Harper - Reinstate Monica
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I installed a new outlet and tripped the whole power panel... Does a 30 amp circuit need special outlets?

So... I tried swapping two outlets in my kitchen, and tripped the entire power panel! The old outlets were wired with FOUR wires: red, black, white, bare. I wired the new outlets using the same scheme: Red to one of the HOT terminals Black to the…
steeveedee
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Neutral pigtails on MWBC

I've recently moved into a new home with a few outbuildings. Due to the property being in rural unincorporated area, no inspections or permitting was required on the outbuildings when they were built last year. To mitigate the risk my insurance…
cyclops
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Splitting 240V into two 120V Circuits

I think I have this figured out for the most part but looking for validation from expert strangers on the internet. Renovated the kitchen in this 1960's house. I think it probably has been renovated before and there was a ton of power in the…
Tyler Herron
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House Wired Incorrectly? - MWBC

I am working on finishing my basement. In my basement there is 3 junction boxes fed by 12/3 wire. Each junction box feeds a single 12/2 line (White-White, Black-Black, Ground-Ground, Red-Nothing). My thought was this was done to allow expansion at a…
Jeff
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Why are tandem breakers on shared neutral (MWBC) problematic?

I hear that shared-neutral or multi-wire branch circuits (MWBC) can have issues when used with tandem breakers (also called duplex, twin, cheater or double-stuff breakers). What is the issue there? Also, how do I put them on GFCI or AFCI?
Harper - Reinstate Monica
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Look over father's plan to fix outdoor electrical circuit

So to begin with, I am not a DIY'er when it comes to electricity. I prefer to allow the professionals to handle these matters as it's not something I'm confident in and not too knowledgeable about... my dad however has always been a DIY'er and I'll…
Austin Stepp
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MWBC and very low power factors

The principle of an MWBC is that two hots can share a neutral if they're on opposite phases, since the current on the neutral will cancel instead of adding. But isn't this only true for loads with reasonable power factors? Consider if one phase of…
Joseph Sible-Reinstate Monica
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Can't figure out this multi-wire branch circuit

I recently replaced my kitchen island, and found out that I have some MWBC in my home. I figured it out and the new receptacles are working. 
On a separate line, at the countertop, I went to replace a working old dirty receptacle with a GFCI…
user241867
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When did Handle Ties become mandatory for MWBC?

Original Question I was extending a circuit in my kitchen last week as part of a remodel and discovered something that had been under my nose the whole time I've lived here but I just paid enough attention to notice. There are 5 multiwire branch…
ThisOneGoesToEleven
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Sharing Neutrals - How To Correct?

I have a 12/3 NM cable landing on two separate 20 amp breakers sharing a neutral between the two. They are landing on a Dishwasher/Garbage Disposal outlet. I understand this is NOT to code since there is no tie bar between the two breakers (confirm…
Richard
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MWBC with both circuits on the same bus -- any easy fixes?

While moving some wires around in my garage (to make space for attic storage), I discovered an electrical issue that might be concerning: In my garage there are two circuits delivered as a MWBC, but the two circuits are on the same bus (0V between…
ldoogy
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Two Circuits on a Single 12/3 - Shared Neutral

I was recently trying to upgrade a 20A breaker supplying outlets in my kitchen and dining room to a CAFCI breaker. When I opened my breaker box I saw that the neutral on this circuit was shared with an adjacent breaker, which supplies our kitchen…
Nigel Crawford
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Multi-Wire Branch Circuit on wrong breakers

My electrical panel has a double-pole breaker that looks like it's for a MWBC, but actually the attached wires are from different cables. In the below picture the black wire with the yellow rubber bands goes out the side of the panel (to a sump…
IceGlasses
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In a multiwire branch circuit, can the two hots be connected to the same phase?

This may be an obvious question, but I haven't been able to find a direct answer. I believe I have a MWBC - I have two hot wires connected to two separate circuit breakers, sharing a neutral and ground wire. The two circuit breakers are not adjacent…
Mwinn
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