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I have a Multiwire Branch Circuit connected to two 15A Breakers (Handle tied together). Each circuit only has 2 duplex receptacles on it that are seldomly used. Is it acceptable to combine both the HOTs together and pigtail to only 1 of the 15A breakers? I would than remove the Handle Tie and use the renamed 15A Breaker for a new circuit.

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    I work with MWBCs quite a lot, and I can't really see a problem with that. That's been proposed to me as a method for validating that an MWBC is not cross-connected with any other circuits. (by using a GFCI to detect cross-connect leakage). – Harper Jul 21 '17 at 17:26
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Since

  1. the two hot conductors do not rejoin at any point (we know this because you'd have a 240V short on your hands otherwise), making it so that the rules about wires in parallel don't apply
  2. the two hot conductors are being protected by the same breaker in the new configuration (i.e. two 14AWG hots on the same 15A breaker, returning via a 14AWG neutral), eliminating the possibility of an overloaded neutral, and
  3. this is all on one breaker, making it all part of one branch circuit and avoiding a violation of 200.4(A) regarding shared neutrals

you can go ahead and do this safely by wirenutting both hots to a pigtail from the chosen breaker in the panel. (312.8 allows splicing in the panel provided you aren't overflowing the gutter space.)

I would put a tag on the wires in the cable saying "Same Leg" at the various boxes this feeds though to avoid confusion between this (admittedly somewhat odd) configuration and an actual multi-wire branch circuit.

  • Some breakers are designed to accept two hots. They typically have a mount with channels on each side of the screw. In that case it's not necessary to pigtail. – isherwood Jul 22 '17 at 14:36
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My only concern comes from the IAEI (International Association of Electrical Inspectors).

*Question: Can a UL Listed product be modified in the field if the manufacturer indicates that the revision is ok and sends out new parts?

Answer: The UL Mark applies to products as they were originally manufactured. UL does not know the effect modifications in the field will have on a product. Therefore, unless the modifications are specifically tested and evaluated by UL, UL cannot say that the modifications void the UL Mark, or that the product continues to comply with UL’s safety requirements. The exception would be when the product has specific replacement markings.*

So why not just replace the breakers, cost is not relevant and everyone is happy.

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    In effect, isn't it the same as having a spare breaker with a handle tie? – Kris Jul 22 '17 at 14:19
  • Have you checked with UL to see if that modification cause that equipment to lose its UL listing. – Retired Master Electrician Jul 23 '17 at 20:16
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Short answer: No, not like that.

You have to remove one of the wires in the panel and cap it off.

Then go to each receptacle that was on that wire and rewire it to the remaining hot wire instead of the disconnected one. Cap off the disconnected wire at each receptacle.

Then you are good.

Good luck and stay safe!

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    I'm not the OP and not a sparky but I'm curious as to why this is required. No wires will be subject to overcurrent as would be if the two hots were to be connected to two breakers on the same leg. Thanks – DoxyLover Jul 21 '17 at 17:34
  • Agreed, but the Electrical Code does not allow paralleling of conductors less than 1/0 with a few exceptions for elevators. And, IMHO, it is better form to have only one wire per breaker. – ArchonOSX Jul 21 '17 at 18:51
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    I'm not seeing how this is "paralleling" if the two never come back together. How is it different than a pigtail in the panel? – isherwood Jul 21 '17 at 19:00
  • Hmmmm good point if they are separate receptacles are not joined in the field then they would not be considered paralleled. One of them should still be re-identified (if they are red and black) so that the next person doesn't think they are different legs of the 240 volt system. They will now be on the same leg. Both wires on the same breaker seems like bad form and may be confusing. – ArchonOSX Jul 21 '17 at 22:01
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    He's not paralleling because each hot serves differeent loads. – Harper Jul 22 '17 at 14:47

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