Using 12-3 romex for multi circuits

[jdub63]

I'm currently installing my electrical outlets and was planning on using 12-3 romex for wiring the quad outlets. My plan was to use one circuit (black) for one side and the other circuit(red) for the other side of the quad. Can I use the same neutral for both circuits?? If I use two 20 amp breakers I should be able to get 26 outlets (13 per circuit) out of one run. Right??

 

[kbs2244]

There may be local codes you need to check out, but I do it all the time.
I don't do Romex, but the concept is the same with 3 wires in EMT.

 

[Charles (in GA)]

I'm currently installing my electrical outlets and was planning on using 12-3 romex for wiring the quad outlets. My plan was to use one circuit (black) for one side and the other circuit(red) for the other side of the quad. Can I use the same neutral for both circuits?? If I use two 20 amp breakers I should be able to get 26 outlets (13 per circuit) out of one run. Right??

In most cases code requires that you use a double pole circuit breaker (aka 240v breaker, one that is actually two breakers with the handles tied together). The reasoning is that if a circuit trips, and you go to work on it, the other circuit will not be hot. Other part of the reasoning, the panelboards are designed so that adjacent breakers are on opposite sides of the buss, which is what you want. If you were to use two breakers that were both on the same side of the buss (electrically) you would be overloading the lone neutral.

You need to split up your circuits more than having 13 on one breaker and 13 on another.

Charles

 

[jdub63]

Thanks. That makes sense...I'll use a double pole breaker. You addressed my concern of overloading the neutral.

I live out of city limits, so no permits/inspections required

 

[sberry]

I use multi wire circuits all the time especially where loads are heavy or runs are long.

 

[Falcon67]

X2 what Charles said.

 

[notquitegto]

I was thinking about doing something similar. You will just wire-nut all the neutrals together? Right?

Are you planning on a double 20amp breaker?

Mike

 

[nate379]

Is there a limit on how many outlets on a run? I have a 20 amp and 2 15 amp run of outlets in my garage and was thinking about putting quad boxes in place of the singles just for having more space to plug stuff in. 2 chargers plugged in and that outlet is done type thing.

The 20 amp has 1 outlet (for a freezer), one 15 amp is for my boiler controller, and the other has 4 or 5 outlets.

 

[malibu101]

.

The 20 amp has 1 outlet (for a freezer), one 15 amp is for my boiler controller, and the other has 4 or 5 outlets.

Smart idea that the freezer is on its own circuit. The amp draw of the freezer probably does not neccesitate its own circuit.
BUT
I have seen and heard of more than one occasion where the freezer was on a circuit with something else and the circuit was tripped for some reason of other things plugged in. The tripped breaker was not discovered until it was too late.

 

[kbs2244]

Don't they put pilot lights on freezers anymore?
Mine have a little orange light by the handle to show that there is power to the unit.

 

[VHF]

If your recepticals don't require ground-fault protection then the shared-neutral multi-wire branch circuit (MWBC) as described is great. However, under NEC all the 120VAC recepticals in a garage with a concrete floor require GFCI protection. The only way to provide this with a MWBC would be to use a GFCI receptical for each outlet, which would get a little expensive.

Far more common is to use either (1.) one GFCI receptical for each circuit and then daisy-chain the rest of the downstream recepticals or (2.) use a GFCI circuit breaker to protect all the recepticals on the circuit. However, neither of these approaches are compatible with a shared neutral. :-(

It's probably better to just run two 12-2 Romex cables when ground fault protection is requried. (Too bad they don't make a 12-4 with ground!)

 

[malibu101]

It's probably better to just run two 12-2 Romex cables when ground fault protection is requried. (Too bad they don't make a 12-4 with ground!)

To inform- I don't know about NM cables but we use 12/4 MC cable all the time.
It has black, red, blue, white, and green conductors. We use it for mainly for applications that are 3Ø and need a neutral.

 

[sberry]

You can protect multi wire branches with gfci, not both circuits at once though.

 

[Aceman]

Here we go again...

However, under NEC all the 120VAC recepticals in a garage with a concrete floor require GFCI protection.

That's not what the nec says. I see no mention of concrete floors? It says GFI protection is required in garages and all work areas except for habitable rooms. 210.8(A)2

The only way to provide this with a MWBC would be to use a GFCI receptical for each outlet, which would get a little expensive.

Or a 2 pole GFI breaker. Not necessarily cheap, but it is an option.

Far more common is to use either (1.) one GFCI receptical for each circuit and then daisy-chain the rest of the downstream recepticals or (2.) use a GFCI circuit breaker to protect all the recepticals on the circuit. However, neither of these approaches are compatible with a shared neutral.

GFI's work on shared neutrals, they just need to be installed after the two circuits split. To put things in perspective, your house is fed with a multiwire circuit. Two hots and one neutral.

It's probably better to just run two 12-2 Romex cables when ground fault protection is requried. (Too bad they don't make a 12-4 with ground!)

They do make 12-4 Romex. http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet6

You can protect multi wire branches with gfci, not both circuits at once though.

Huh?

 

[walrus]

Far more common is to use either (1.) one GFCI receptical for each circuit and then daisy-chain the rest of the downstream recepticals

This should work in MWBC, if you use 2 GFCI recepts, one on each circuit and then regular recepts downstream

 

[sberry]

GFI's work on shared neutrals, they just need to be installed after the two circuits split.

That is what I meant, just didnt word it right.

 

[VHF]

Aceman,

Thanks for correcting my attempt to insert concrete floors into the NEC!

They do make 12-4 Romex. http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet6

Wow, and there's even a choice of color-coding for applications (such as this) when you want 2 neutrals. But I bet you won't find it on the shelves at the big box stores, and probably special order at all but the largest supply houses.

If the distance from the pannel to the first outlet location is long, then it might make sense to run a shared-neutral MWBC (using 12/3 NM) to the first location (which would have two GFCI recepticals), and the wiring the rest of the circuit(s) downstream using separate neutrals.

However, much as the elegant thriftiness of MWBC appeals to me, I probably wouldn't do it myself because of (1.) the inconvience of having both circuits trip together on overload, (2.) the (small) chance of frying tools & appliances due to a loose neutral causing an over-voltage condition, and (3.) I prefer GFCI breakers over GFCI recepticals anyway. But I'm going to have to get some of that 12/4 with dual neutrals when the time comes to finsih my garage wiring if I don't use conduit!