15 amp and 20 amp circuits sharing the same neutral

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Stevenfyeager

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electrical contractor
In a remodeling house, there are several 12-3 runs using two 20 amp circuit breakers on each 12-3 cable. Fine enough, but my question is, would it be acceptable to change one of those 20 amp CBs to a 15 amp circuit breaker? Is it ok to share a neutral with two different amperages? Thank you.
 
Not weird at all. I have used MWBCs when relocating a panel during an upgrade, and ended up with one 15a and one 20a circuit sharing a cable. As long as the shared neutral is sized for the larger circuit, you're golden (just as with shared EGCs)
 
I agree also that a multiwire branch circuit (MWBC) that is a 12-12-14 (20A - Neutral - 15A) is perfectly Code compliant. I see this in residential dwellings that were wired with EMT, FMC or other raceway during the mid Twentieth Century, here in the Minneapolis area. The most common recurring scenario is a Laundry branch circuit and a General Lighting branch circuit paired in a MWBC; or a single Small Appliance branch circuit paired with a General Lighting branch circuit.
 
Dennis Alwon said:
The problem would be with afci breakers, if applicable, unless you have a ge panel.
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Dennis never heard about that for a GE panel and was curious about that. Also wouldn't that also apply for gfci breakers?. Electrician for 27 years but do commercial and industrial

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There's no problem with a 15-amp breaker protecting a 12-gauge wire, but in a multi-wire branch circuit, the breaker needs to open all ungrounded conductors simultaneously.
 
drcampbell said:
There's no problem with a 15-amp breaker protecting a 12-gauge wire, but in a multi-wire branch circuit, the breaker needs to open all ungrounded conductors simultaneously.
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Good point, the OP mention changing a 20 amp CB to a 15 which would require a handle-tie.
 
drcampbell said:
There's no problem with a 15-amp breaker protecting a 12-gauge wire, but in a multi-wire branch circuit, the breaker needs to open all ungrounded conductors simultaneously.
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But, they do not need to be common trip, they only need to disconnect them simultaneously so a 15 and 20 with handle ties would be fine.

Roger
 
davegerver said:
Dennis never heard about that for a GE panel and was curious about that. Also wouldn't that also apply for gfci breakers?. Electrician for 27 years but do commercial and industrial

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As stated if you have them both on a 15 amp circuit it is not an issue but if you want one on a 20 and the other on a 15 amp then ge is the one company that makes afci's without any gfp in it so you use 2 sp afci's and use a handle tie.
 
I think you will be out of luck for a multiwire branch circuit with gfci breakers as they would need to be a dp. Unless you can find a dp breaker -(gfci) with a 15 and 20 amp- you won't...:)

In that case just use gfci receptacles at the box where the multiwire branch circuit first terminates.
 
davegerver said:
Dennis never heard about that for a GE panel and was curious about that. Also wouldn't that also apply for gfci breakers?.
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The 20A / 15A Multiwire Branch Circuit is ONLY solvable with GE "MOD3" single pole Combination-Type AFCI breakers. Dual Function AFCI breakers or GFCI breakers cannot be used because of the ground fault sensing of differential current between the Hot and the Neutral.

The "MOD3" is what has been sold to us for at least four years now. The GE MOD3 Combination-Type AFCI is PURE AFCI detection without any ground fault sensing component in its circuitry. The branch circuit load neutral doesn't even have to be connected to the AFCI breaker LOAD terminal, rather, the branch circuit load neutral can be landed directly on the panel neutral bar with the GE Manufacturer's instructions blessing. GE documents how to do this. GE documents the use of a handle tie for two single pole breakers (two AFCI or an AFCI and a conventional OCPD) on a MWBC.

The 20A / 15A MWBC is the hardest AFCI puzzle in the panel upgrade of an existing Dwelling service center. ONLY a GE AFCI can handle the challenge with minimal cost and effort, in my opinion.
 
al hildenbrand said:
The 20A / 15A MWBC is the hardest AFCI puzzle in the panel upgrade of an existing Dwelling service center. ONLY a GE AFCI can handle the challenge with minimal cost and effort, in my opinion.
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Unless you moved the panel more then six feet in the upgrade process - it is not a problem.
 
kwired said:
Unless you moved the panel more then six feet in the upgrade process - it is not a problem.
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Well, yeah, if you don't have to use AFCI, then putting OCPDs on a 20A / 15A MWBC does not have an AFCI's puzzle . . . :blink:

That doesn't change the difficulty, in any way, when one does have to use AFCI.
 
al hildenbrand said:
Well, yeah, if you don't have to use AFCI, then putting OCPDs on a 20A / 15A MWBC does not have an AFCI's puzzle . . . :blink:

That doesn't change the difficulty, in any way, when one does have to use AFCI.
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:D

Roger
 
Sorry never heard of the "mod 3" breakers. Dont know if I would trust them without sensing the neutral as well. Probably great for those nuisance trips

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davegerver said:
Dont know if I would trust them without sensing the neutral as well.
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The GE AFCI breaker, as well as all AFCI overcurrent protective devices and AFCI receptacle devices are ONLY testable by their TEST button. There is no third party diagnostic tool or technique that is allowed by the nationally recognized testing laboratories (NRTLs) to "test" any AFCI.

Manufacturers have stonewalled us for over two decades when it comes to sharing technical explanations of their own circuitry solutions to the "Grand Concept" of Arc Fault Circuit Interruption.

As a result, if an AFCI stays "ON," after a TEST and RESET, it is, by definition, working to UL standard until a court of law finds otherwise.
 
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