Current on a 12 gauge wire

[Larry Caldwell]

We are building a home in the country and there are no building inspections or code requirements in this area. I've told the builder that we want to at least meet all the code requirements even though there will not be any official inspections. So, here's the question: There are (2) romex 12/3 wire with ground running thru conduit (with water pipes) to the kitchen island. Supposedly there are (2) single pole 20 amp breakers tied into these wires somehow. I suspect the black wire is tied to one breaker and the red is tied to the other breaker. The primary current loads are:
- Dishwasher - calls for it's own 15 amp breaker
- 2 gallon hot water heater under the sink - probably a 1500 watt heating element (~12 amps)
- small appliance outlets - about 1500 watts for an electric skillet or waffle iron.
1st, I don't see how (2) 20 amp circuits can carry that load. I talked to the electrician and he says "not to worry, it's fine". (I've seen 12 gauge wire on a 30 amp breaker around here and I know that is NOT "fine".) It seems to me that the electrician is using a single 12 gauge neutral to carry the current from (2) 20 amp hot wires and the electrician tells me that 12 gauge can do that. :shocked: Nor do I understand how he's going to provide for the 3 circuits with 2 circuit breakers. I suppose that if we sequence the usage "properly" everything will work.

Am I behind the times? or am I missing something? I'm getting ready to tell the builder to stop work until this is fixed, but don't want to do that unless I'm right. Any thoughts?

Yes, your kitchen is thoroughly under-wired. You need separate circuits for the refrigerator, microwave, garbage disposal and dishwasher. You need a minimum of two 20-amp circuits for receptacles, and a separate 15 amp circuit for lighting. The receptacle circuits need to be on a GFI breaker, and a shared neutral will trip any GFI immediately. It will not work. The water heater needs a 30 amp circuit on 10 gauge wire. That's 8 circuits for a modern kitchen.

 

[LittleBill21]

. The receptacle circuits need to be on a GFI breaker, and a shared neutral will trip any GFI immediately. It will not work. .

This is nonsense. it most certainly works. if your gfci is tied in down stream of the shared neutral distribution. your entire panel is "shared neutral" anyways, mwbc doesn't change this.

 

[LD1]

Way too many people are severly mis informed about how both mwbc's and gfi's work

 

[aczlan]

Yes, your kitchen is thoroughly under-wired. You need separate circuits for the refrigerator, microwave, garbage disposal and dishwasher. You need a minimum of two 20-amp circuits for receptacles, and a separate 15 amp circuit for lighting. The receptacle circuits need to be on a GFI breaker, and a shared neutral will trip any GFI immediately. It will not work. The water heater needs a 30 amp circuit on 10 gauge wire. That's 8 circuits for a modern kitchen.

As has been said, you need either a 220V GFCI breaker, or two GFCI receptacles after you split off the neutral to the two directions.

Aaron Z

 

[LD1]

It's wired the same as any other GFI outlet. The GFI don't care what is shared on the neutral on the line side. GFI only senses neutral current on the load side.

You don't tie in the load side neutral to the line side neutral on a mwbc just like you wouldn't on a normal circuit.

 

[ray66v]

It's wired the same as any other GFI outlet. The GFI don't care what is shared on the neutral on the line side. GFI only senses neutral current on the load side.

You don't tie in the load side neutral to the line side neutral on a mwbc just like you wouldn't on a normal circuit.

Are you saying, you can successfully cascade GFI's on a mwbc, if you don't use the line terminals of the GFI's?

 

[buickanddeere]

As has been said, you need either a 220V GFCI breaker, or two GFCI receptacles after you split off the neutral to the two directions.

Aaron Z

A 2 pole GFCI breaker will trip when 120V loads are supplied from it.

 

[buickanddeere]

How does anyone imagine that a GFCI receptacle/breaker supplying a fridge makes the world a better place?
How does anyone think that sharing a fridge circuit and breaker with another load makes the world a better place ?

 

[LD1]

Are you saying, you can successfully cascade GFI's on a mwbc, if you don't use the line terminals of the GFI's?

Not sure what you are asking.

If you want to use a MWBC to make TWO circuits that share a neutral, and you want BOTH of those circuits GFI protected, You run the Black and shared white wire from MWBC to the line terminals of the 1st GFI. You run the Red and the shared white to the other GFI.

From the GFI's, you wire everything downstream off the load side of the GFI's, just as you would with a normal circuit. From the GFI onward, is 12/2 wire and NO neutral sharing.

 

[ray66v]

Not sure what you are asking.

If you want to use a MWBC to make TWO circuits that share a neutral, and you want BOTH of those circuits GFI protected, You run the Black and shared white wire from MWBC to the line terminals of the 1st GFI. You run the Red and the shared white to the other GFI.

From the GFI's, you wire everything downstream off the load side of the GFI's, just as you would with a normal circuit. From the GFI onward, is 12/2 wire and NO neutral sharing.

That's a clear way of stating it.

My question was, what if you wire 4 GFI's on one 12/3 MWBC, alternating them as you go, black leg, red leg, black leg, red leg, wired by the line terminals only, sharing the neutral as you go? Would that work?