Thread: 2 pole breakers used for 2 single pole circuits

Guys,
A while back we had a thread discussing a new trend in new construction of using a double pole breaker for 2 single pole circuits and that this was allowed by the NEC. I can not seem to find that thread in the archives. I need to have some back up to explain this practice to some doubting realtors. Can anyone point me to that thread or some documentation that explains the reasoning behind this practice?

Thanks Much

Jim Weyenberg
HouseMaster Inc of NE. WI.

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Jim,

Originally Posted by Jim Weyenberg

A while back we had a thread discussing a new trend in new construction of using a double pole breaker for 2 single pole circuits and that this was allowed by the NEC.

If those are actually separate circuits, there is nothing wrong with using double pole breakers for two circuits, just be aware that when one circuit trips its side of the breaker the other side will trip off the circuit on it.

some documentation that explains the reasoning behind this practice?

What I think you really have is not two separate circuits but a multiwire circuit which has two 'hot' conductors and one 'neutral' conductor, and they are both fed off a double pole breaker, which is now required and has always been a very good idea.

Follow the conductors from the breaker next time and you will probably find that they go to a 3-conductor with ground NM cable, that would be a good indication that is a multiwire circuit. Use your multimeter and check the voltage between the two hot conductors - there should be 240 volts, which leaves 120 volts each leg to neutral and ground. If you find -0- volts between the two hot conductors and it is a 3-wire cable, that is wrong, very wrong as you could have twice as much current on the 'neutral' as it was designed to have on it - and that would not be good.

Thanks Jerry,
But let me see if I understand you correctly. So if they are 2 separate circuits but share a neutral, the double pole breaker makes sure that if one single pole is tripped the other is simultaneously tripped to prevent the shared neutral from remaining hot, both circuits broken for safety sake. Reason being to save some copper? I would guess!

Jim Weyenberg
HouseMaster Inc. of NE. WI.

Originally Posted by Jim Weyenberg

So if they are 2 separate circuits but share a neutral,

The shared neutral makes them not "two separate" circuits, it makes it "one" multiwire circuit.

the double pole breaker makes sure that if one single pole is tripped the other is simultaneously tripped to prevent the shared neutral from remaining hot,

The neutral does not remain "hot" but what the double pole breaker does is make sure the current from the other leg of the multiwire circuit also stops flowing through the neutral, otherwise you could disconnect the neutral and have a lot of current flowing through it, making for one large arc, and resulting affects, which could include fire, electrical shock, etc.

The double pole breaker shut off

both circuits broken for safety sake.

Reason being to save some copper?

I've never found a good reason to use multiwire circuits, but, yeah, it would save some copper, some labor, but not enough to offset the potential for bad things to happen. Note, though, that multiwire circuits have been around a very long time.

The National Electrical Code, NEC, is written as a restrictive document. What this means is that unless something is prohibited, or directed to be done a certain way, it is permitted. You aren't going to find a paragraph that says it's OK to put 2 circuits on a 2 pole breaker, only a paragraph that says it's not OK if it isn't (and there isn't one, by the way)

Multi wire branch circuits save copper. 2 separate circuits require 2 hots, 2 neutrals, and 2 grounds and a multi wire requires 2 hots, 1 neutral, and 1 ground. Multi wire circuits also help limit voltage drop. The savings are even more pronounced in 3 phase applications.

While 2 pole breakers are acceptable on multi wire branch circuits, 2 singles with handle ties are a better option if there are no line to line (hot to hot) loads. The handle ties are designed so the handle on a tripped breaker can move without shutting off the other breaker but when operating the handles manually both breakers shut off per NEC rules. Note that APPROVED handle ties are required.

Jerry mis-spoke on the testing of multiwire circuit voltage. You should have ~240 volts betweel the 2 hot wires on a correctly wired one and will have ~0 volts between hot wires on an incorrectly wired one. Assuming you get 120 volts between the 2 hot wires a different kind of wiring issue is at hand where one hot wire has been wired as a neutral rather than just having the 2 hot wires on the same line circuit. The line to neutral voltage should always be ~120 volts, even if the hots are on the same line circuit. Any other voltages indicate the neutral is open somewhere.

Originally Posted by Bill Kriegh

Jerry mis-spoke on the testing of multiwire circuit voltage. You should have ~240 volts betweel the 2 hot wires on a correctly wired one and will have ~0 volts between hot wires on an incorrectly wired one.

Originally Posted by Jerry Peck

If you only find 120 volts between the two hot conductors and it is a 3-wire cable, that is wrong, very wrong as you could have twice as much current on the 'neutral' as it was designed to have on it - and that would not be good.

Bill is quite correct, my head must have been somewhere else as you will get ~0 volts between the two hots on a mis-wired multiwire circuit.

Bill, thank you for catching and correcting that. I am going back to change in so as not to confuse others if they read that post and do not read the corrections below it.

Thanks, Jerry and Bill,
You guys are indispensable. I see what you mean and see it going back to the old fuse box circuits. Thank you both for the help.

Jim Weyenberg
HouseMaster Inc. of NE. WI.