[rcolmansr75]

My inspector says I can't do this. Like running a 12/3 for the two circuits for the kitchen and using neutral to black for one and neutral to red for the other.

Is this the case? If so when was it changed

Dick

 

[Jim Port]

What you describe is called a multi-wire branch circuit. Depending on the code cycle you need afci protection for that circuit. Two pole afci breakers are only available for certain panels.

 

[joed]

Add your location. Give us more detail of exactly what you are attempting to do.
I know of no place where this is banned by code. It could be expensive if you are required to have AFCI or GFCI protection, like in a kitchen, which you mention.

 

[rcolmansr75]

Yes the Murray 20-Amp Double-Pole Type MP-AT Combination AFCI-Circuit Breaker Will fit my panel.

 

[Oso954]

"Will fit"my panel isn't good enough. It has to be listed for your panel. Is your panel also a Murray ?

 

[jeffnc]

What you describe is called a multi-wire branch circuit.

My understanding is that a multi-wire branch circuit requires a little more than just what the OP said. For example, the 2 hot wires should have a voltage between them. There is also more detail to ensure the neutral doesn't become overloaded. I think someone should add in more detail here before someone burns up a TV or worse - a house.

 

[Oso954]

My understanding is that a multi-wire branch circuit requires a little more than just what the OP said. For example, the 2 hot wires should have a voltage between them. There is also more detail to ensure the neutral doesn't become overloaded. I think someone should add in more detail here before someone burns up a TV or worse - a house.

That's redundant. If the 2 hot wires show voltage (240v) between them, there is no overloading the neutral, it will only see the difference in the neutral current.
The problem is when each wire has voltage but there is no voltage between them. That is when you get the sum of currents on the neutral, which can overload it.

I think Jim put the proper name on it and I assumed a properly wired MWBC. The question is why can't he use it? We have been chasing the AFCI question. In re-reading the OP's question, he never said it was for the kitchen. He said "like running .... For the kitchen". So we need to ask is this really for the kitchen, or is it a circuit for some other use or another location ?

 

[jbfan]

My inspector says I can't do this. Like running a 12/3 for the two circuits for the kitchen and using neutral to black for one and neutral to red for the other.

Is this the case? If so when was it changed

Dick

Did he cite a code section as a reason, or just his not liking them.
As others have said, it may be the fact of needing a 2 pole AFCI breaker, and not finding one for your panel.

 

[jeffnc]

In re-reading the OP's question, he never said it was for the kitchen. He said "like running .... For the kitchen". So we need to ask is this really for the kitchen, or is it a circuit for some other use or another location ?

That's the point - he didn't say "a circuit", he said "two circuits". Normally, 2 separate circuits shouldn't share a neutral. So I don't agree with Jim - the OP didn't describe a multiwire branch circuit - not specifically.

 

[Tom738]

That's the point - he didn't say "a circuit", he said "two circuits". Normally, 2 separate circuits shouldn't share a neutral. So I don't agree with Jim - the OP didn't describe a multiwire branch circuit - not specifically.

OK, what's the difference between the described situation of 2 separate circuits sharing a neutral on a 12-3 wire and an MWBC? Is it that there are some places where code requires a dedicated circuit for a certain use that is incompatible with an MWBC and therefore you can't use an MWBC?

 

[joed]

Sorry to say but this

Like running a 12/3 for the two circuits for the kitchen and using neutral to black for one and neutral to red for the other.

is the description of a MWBC,

 

[Jim Port]

OK, what's the difference between the described situation of 2 separate circuits sharing a neutral on a 12-3 wire and an MWBC? Is it that there are some places where code requires a dedicated circuit for a certain use that is incompatible with an MWBC and therefore you can't use an MWBC?

One or both circuits could still be dedicated even with the shared neutral.

Two circuits sharing a neutral is the definition of a MWBC.

 

[rcolmansr75]

Yes it is for the kitchen counter receptacles,

I was working from B&D wiring guide 6th addition.

They called it "Double receptacle circuit with shared neutral wire"

I know I need GFCI receptacles on the counter and AFCI in the breaker box. He objected to me using a 12/3 to connect these because of the shared neutral. Said I needed 2 separate 12/2 circuits

 

[darren]

I know I need GFCI receptacles on the counter and AFCI in the breaker box. He objected to me using a 12/3 to connect these because of the shared neutral. Said I needed 2 separate 12/2 circuits

If you have two separate AFCI breakers than you would need two 12/2, you can not share a neutral in this case.

If you have a 2pole AFCI breaker your 12/3 would be good.

 

[AllanJ]

Subtle restriction with multiwire branch circuits (shared neutral circuits) and ground fault circuit interrupters.

You cannot continue from the load terminals of a GFCI receptacle down the same 3 wire cable that the other half of the MWBC continues down.

Meanwhile ...

You can branch off of an MWBC using the load terminals of a GFCI receptacle continuing down a separate 2 wire cable.

You can install any number of GFCI receptacle units along a MWBC leaving the load terminals empty.

A 2 conductor cable branch off from an MWBC can reconvene with the MWBC in an outlet box or junction box further downstream subject to adequate box size and no connection between the MWBC neutral and the separate cable neutral at that location (instead having separate bundles of white wires).

Actually for any two feed cables entering the same box, regardless of origin of those cables, their neutrals may not be connected together in that box and also loads or continuing cables may not be connected to the neutral of one feed cable and the hot of the other feed cable. I will admit to seeing this rule broken where two cables came up from a 2 gang switch box to a ceiling fixture with separate leads for a light and a fan but only one neutral going into the fixture.

 

[jeffnc]

Two circuits sharing a neutral is the definition of a MWBC.

No Jim, that is not how the definition is written, as you should know, and as you probably do know. The hot leads must be connected to out of phase sources. The OP did not describe how the circuit was wired. Clearly, if the hots are not wired correctly at the panel, the neutral will be overloaded with "return" current.

http://www.nachi.org/forum/f19/explaining-multiwire-circuits-fun-3038/

https://www.mikeholt.com/mojonewsar...ngDangersMultiwireBranchCircuits~20020218.htm

 

[joed]

It is still a multi wire circuit. Just because someone installs it wrong doesn't make it not a MWBC.

There is no doubt that installed wrong a neutral can overheat.

 

[jeffnc]

We didn't say "multi wire circuit". We said "multiwire branch circuit". It has a definition. The definition isn't "more than one wire on a circuit." Just any two black wires coming from the same side of the panel won't have a voltage between them.

All the OP said was "shared neutral". You can easily have a shared neutral with 2 hot wires and it's not a multiwire branch circuit. The OP didn't say how it was wired nor what the inspector objected to.

Branch Circuit, Multiwire.
A branch circuit that consists
of two or more ungrounded conductors that have a voltage
between them, and a grounded conductor that has equal
voltage between it and each ungrounded conductor of the
circuit and that is connected to the neutral or grounded
conductor of the system.

 

[partner]

Add your location. Give us more detail of exactly what you are attempting to do.
I know of no place where this is banned by code. It could be expensive if you are required to have AFCI or GFCI protection, like in a kitchen, which you mention.

I bought and moved into a new house about a year ago. While looking over my breaker panel back then, I noticed something that looked odd, at least I had never seen before. Two circuits, dishwasher and garbage disposal were sharing a 15A double breaker with a single switch. Google quickly told me that it was a MWBC and acceptable. Now reading this thread I see that a AFCI or a GFCI may be required. Neither are on these circuits. There are about 10 AFCIs in my box and the house is full of GFCIs but none on these circuits. Is there a code violation here?

 

[joed]

Not a code issue in Canada, but not sure about NEC. I don't think AFCI is required here, but maybe GFCI.