Breakers designed for 2 conductors vs 2 circuits

Interesting topic came up the other day at a commercial inspection with older Square D OCPD’s designed for 2 conductors.

While I had a panel open, there happened to be an electrician there at same time looking at panel at same time as me.

While looking in the panel, we both noticed a few breakers in the panel that 2 conductors, he pointed out he will be writing up to trace and service along with other defects in there, as there were.

I guess he thought I’d say something, he remarked that these types of breakers create a lot of confusion and that the breakers are designed for 2 conductors not 2 circuits, and based on the other sloppy work they were just looking for a shortcut. He said that property inspectors are correct in not making an issue out of it, but most don’t understand the difference.

Interesting point… 2 conductors vs 2 circuits.

I would like to hear his description of the difference in that context. Interestingly “electrical circuit” and “circuit” are not defined in the NEC.

Would 2 conductors/1 circuit involve a shared ground??? I don’t see how that would work. Inquiring minds want to know…

In passing I didn’t get too much in regards to specifics, but understood his point to be where conductors could be maybe for specific components or areas having their own circuit? I could see a circuit for say a FAU and a small appliance circuit end up on the same OCPD and we’d never know?

The aggregate demand needs to be within the capacity of the breaker, so you can’t just willy-nilly stick double the load on the breaker. They need to know what they are doing and what kinds of demands they are combining, but I would still perceive them as separate circuits.

Trying to figure out if there is something for me to learn from his comment. If so, I’d like to capture it.

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If two circuits are required then yes installing both hot legs on a single circuit breaker is not going to satisfy that code requirement, but as Chuck stated you cannot determine that by simply looking at the two conductors terminated on a single CB. You would need to investigate where those conductors went and what they were supplying. Two conductors on a CB can be perfectly legal when done correctly.

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Agreed. For my part, I made note of the other defects as I should. I thought was interesting two different perspectives, as Chuck also stated, if there’s something to learn that’s awesome.

It sounds to me that he may be discussing parallel circuits (two wires going to one device).

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I could be reading your question completely wrong so do keep that in mind. If the two circuits you are referring to are part of a multiwire branch circuit then a two pole breaker would be one way to comply with the requirement for common shut off. Given the common disconnect aspect of the breaker when tripped it would be less convenient but that does not make it a violation of the National Electric Code (NEC). The other way to protect a multiwire branch circuit is to use 2 separate breakers with a handle tie to assure common opening when using the two breakers as a 2 pole switch.

If the 2 circuits you are referring to are each 2 wire then it would be poor practice. But again I know of no NEC prohibition of doing it that way.


Tom Horne

No. It wouldn’t work that way. A MWBC must have 240V potential to avoid overloading the shared neutral.

Also, with a single pole breaker, the combined capacity can’t exceed the capacity of the breaker.

What wouldn’t work what way? Without the quote link there is no way to tell what you are referring to.


Tom Horne

There. Fixed it for you. Given that your’s was the only post mentioning MWBC and it immediately followed your post in the thread, I thought you might be able to make the leap on the post/response relationship.

In any case: No. It would not conform to the NEC requirements for an MWBC.

May I ask you for chapter and verse on that? What code section forbids the use of a double pole breaker as the Over-Current Protective Device for a multiwire branch circuit?


Tom Horne

The breaker we are discussing is a single pole, not a double pole. But to answer your question, we need go no further than the very first instance of the term multiwire branch circuit in the NEC (i.e., the definition).

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.

Note that the definition includes the phrase “two or more ungrounded conductors that have a voltage between them”. Two conductors connected to the same terminal cannot have a voltage between them. What you described does not meet the definition, nor could it provide the function of an MWBC.

If you use some deductive logic, you can probably suss out what post this is in response to.

Two conductors terminating in/on one OCPD is not usually typical but by the same logic not typically unusual unless I am reading the post wrong, which I have been known to do.
Post: "While looking in the panel, we both noticed a few breakers in the panel that 2 conductors, he pointed out he will be writing up to trace and service along with other defects in there, as there were.

I trace branch circuits back to the source, when required. I also do circuit drop voltage.

Old article: Still applicable today, I think?

How To Correct Double Tapped Circuit Breakers

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Chuck

Did you miss the first sentence were I said that “I could be reading your question completely wrong so do keep that in mind.” Then in each of the cases I laid out that I was writing about Multiwire Branch Circuits.

I apologize for any confusion I caused but after reading my posting again I do not find any technical errors in it. I simply misunderstood the nature of the original question.

Getting back to the original question I would point out that many currently manufactured single pole circuit breakers are intended to accommodate the termination of 2 separate conductors provided that both are the same size and material. One example is the Square D QO series which has a SEMS machine screw at each terminal. Running 2 portions of the same branch circuit from the terminal of such a breaker does not seem like terrible practice to me. Many times on larger electrical projects the electrical engineer had called out such arrangements in the notes and panel schedule. As long as it is done in a “Neat and workman like manor” I don’t see a problem. Perhaps it is the absence of an accurate panel schedule in many installations which causes the misunderstanding of what the two conductors might be. In a commercial property checking the “As Built” electrical drawings might explain many things without any need to do the extra work of tracing the circuit wiring from the breaker to see what the conductors actually supply.


Tom Horne

His statement is ‘kinda’ true. He may know more about the load of each conductor’s “circuit”.

use 180va if you want to know the true load. Each conductor could be maxed out.

Gentlemen, great conversation! I’m trying to learn as much as possible about the electrical side so I understand more of the crazy stuff I come across.

Given that breakers ‘can’ be double tapped if breaker allows, why would I be ‘tracing’ any part of the branch circuit wiring? That would be waaaay outside of my scope… unless some of you are full fledge building inspectors or are just exceeding the standard?

I’ll be viewing that link about correcting double taps next!
Thanks for the education!

Great link to show the simple fix. Thanks

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You are quite welcome.

The sum of the defect, extending a breach circuit, is OCP. Over Current Protection. Pig Tailed termination aligns 2 conductors to terminate once under a lug maintain a single circuit. Drop voltage on 15 and 20 amp circuits should be analysed at receptacles downstream moving up stream to determine adverse average current. I use 8.4% and higher as a threshold in my reports. I will as a link when I return from work.

If you are learning then start with using the correct terms.

Doubled taps does not appear in the NEC.

State what you SEE. Example. Two wires under the same terminal.

Use caution when citing the code.