14/3 feeds 2 circuits, shared neutral?

[54FordPanel]

I'm helping my nephew remodel his house, which was built in the late '70s. I've found at the breaker box that they are using 14/3 to feed 2 different circuits, and sharing the neutral.
This is original wiring from the builder, not a previous owner.

Is this ok? Doesn't 2 circuits sharing the neutral double the load on the neutral?

There are 2 different 14/3 wires feeding 4 circuits off 4 breakers that are doing this.

I have to move these wires anyway, and I need to know if it's ok to do it this way, I'll replace it with 14/3 again. Otherwise, I'll run new 14/2 wires to do it right.

 

[Aceman]

Is this ok? Doesn't 2 circuits sharing the neutral double the load on the neutral?

Yes, it's ok and no, it doesn't double the neutral load. This is assuming it's done right and that both "hots" haven't been pulled from the same phase.

 

[54FordPanel]

Ok, I've been a'Googling since I posted this, and it's called a multi-wire branch circuit? And as long as the 2 circuits are on different phases it's ok?

Edit: Looks like we're posting at the same time. Thanks, that's the info I needed Ace

 

[VHF]

Yes, multi-wire branch circuit (MWBC). As long as the two hots are on separate legs it's OK. If the two hots were on the same leg, then the neutral could be overloaded.

 

[davido30093]

MWBC are commonly used to save cost. The load on the nuetral is the difference in the two loads. i.e. If the load on one circuit is 10 amps and the load on the other circuit is 5 amps, the load on the nuetral is the difference, 5 amps.

 

[walrus]

Current code makes you use a 2 pole breaker. Back in the 70s you could use two single pole breakers.

Waiting for the naysayers to say the house will burn down if you use a MWBC. Oh Wait its been like that since the 70s? you sure the house is still standing?

 

[APEowner]

Current code makes you use a 2 pole breaker. Back in the 70s you could use two single pole breakers.

I would upgrade to this. I really don't care for any situation where you need to turn off two breakers to kill all the power in one box. Yes it can happen in a completely up to code situation and yes you should really make sure all the wires in a box are dead before you mess around in there but it's so easy to avoid and sooner or later it's going to bite someone (and it might be you).

 

[Gooch]

I would upgrade to this. I really don't care for any situation where you need to turn off two breakers to kill all the power in one box. Yes it can happen in a completely up to code situation and yes you should really make sure all the wires in a box are dead before you mess around in there but it's so easy to avoid and sooner or later it's going to bite someone (and it might be you).

I agree, but make sure you are ok with if something causes on leg to short or overload that both legs will be tripped, or that if you need to work on one leg, that you will be shutting off the other leg aswell.

 

[cowboyjosh]

I agree, but make sure you are ok with if something causes on leg to short or overload that both legs will be tripped, or that if you need to work on one leg, that you will be shutting off the other leg aswell.

Or you could use handle ties if they make them for whatever brand panel your working with. Your AHJ is probably different, but our AHJ still allows MWBC breakers to be handle tied as opposed to a double pole breaker.

 

[jvitez]

To be really particular, you could tie the two handles of the individual breakers together. Go to an electrical supply house and see what they have for your brand. Or, you could just leave it for another 30 years and see what happens.

We use this type of circuit very often in Canada. Only relatively recently were single 20 amp circuits allowed for kitchens, like the NEC. The CEC demanded multi-branch wiring so that the top plug of one receptacle was on one circuit, and the bottom plug was on the other, so a kettle and toaster could be plugged in at the same time to the same receptacle. We mostly use 15 amp circuits for residential construction.

My garage has several of these circuits. 14/3 for 2 circuits is cheaper and somewhat less labour than 2 runs of 14/2.

 

[Charles (in GA)]

I think code just calls for a common trip, it doesn't get as specific as having a double pole breaker.

210.4(B) Disconnecting Means. Each multiwire branch circuit shall be provided with a means that will simultaneously disconnect all ungrounded conductors at the point where the branch circuit originates.

Charles

 

[Gooch]

I think code just calls for a common trip, it doesn't get as specific as having a double pole breaker.

210.4(B) Disconnecting Means. Each multiwire branch circuit shall be provided with a means that will simultaneously disconnect all ungrounded conductors at the point where the branch circuit originates.

Charles

right, but a finish nail does not comply. you need to buy a specific handle tie, and for the price of most 2 pole 15 and 20 amp breakers, this is the quickest way.

 

[Gooch]

To be really particular, you could tie the two handles of the individual breakers together. Go to an electrical supply house and see what they have for your brand. Or, you could just leave it for another 30 years and see what happens.

We use this type of circuit very often in Canada. Only relatively recently were single 20 amp circuits allowed for kitchens, like the NEC. The CEC demanded multi-branch wiring so that the top plug of one receptacle was on one circuit, and the bottom plug was on the other, so a kettle and toaster could be plugged in at the same time to the same receptacle. We mostly use 15 amp circuits for residential construction.

My garage has several of these circuits. 14/3 for 2 circuits is cheaper and somewhat less labour than 2 runs of 14/2.

\really, that's pretty silly to wire a kitchen that way IMO

 

[mrb]

\really, that's pretty silly to wire a kitchen that way IMO

different countries have different codes. look how the UK wires their houses and you wont think canadas that bad.........

 

[Teken]

\really, that's pretty silly to wire a kitchen that way IMO

Not sure if this is *common* in Canada per say. As I have not seen too many houses wired this way.

Having said all of that . . . One only needs to travel to Ontario where Holmes On Homes is being filmed.

So, I am sure you will see more than a few eye openers there!

 

[Charles (in GA)]

right, but a finish nail does not comply. you need to buy a specific handle tie, and for the price of most 2 pole 15 and 20 amp breakers, this is the quickest way.

I agree. The package with the handle ties is probably $4 or $5 and the DP breaker is only about $7. Reuse the single pole breakers for other circuits.

I think it is a waste to try to wire multi-wire circuits for general purpose receptacles. I did MW circuits for my lighting, but wanted to put 4 ea 4.0 amp fixtures on each 120v circuit and this was maxing out the 80% rule, so I opted for three MW circuits with two lights on one side and two lights on the other side of the circuit. Most of the circuit is in the roof area where it gets hot, so that was a consideration also.

Charles

 

[VHF]

\really, that's pretty silly to wire a kitchen that way IMO

My 1970 tract house in Wisconsin was like that. Makes sense because you can plug in a toaster and waffle iron at the same place and they will be on different sides of the MWBC. So I think it was actually rather intelligent.

However, it makes it a bit of pain to retrofit for GFCI. I ended up just putting a GFCI receptical at each countertop outlet (only 3 total) alternating which hot leg I used.

 

[snorky18]

Assuming the MWBC is allowed by AHJ and wired correctly (ie hots on 2 seperate phases with 240V between them), what are the disadvantages to MWBCs?

Advantage seems like a lot of wire saved if you're building a larger house with long home runs where you can run one 12/3 and split it downstream compared to running two 12/2s, correct?

 

[Charles (in GA)]

Assuming the MWBC is allowed by AHJ and wired correctly (ie hots on 2 seperate phases with 240V between them), what are the disadvantages to MWBCs?

Advantage seems like a lot of wire saved if you're building a larger house with long home runs where you can run one 12/3 and split it downstream compared to running two 12/2s, correct?

Not sure how arc fault breakers would work on MW circuits, of course, AFCI is now required in residential.

Charles