3 Phase Panel with jumper at hot busbars?

This is the main panel (only panel) in a small ranch style home from today. Backfed 100 amp breaker with jumper at busbar. Doesn’t look right to me. Any opinions about the jumper? Other than 100 amp breaker is not secured in place.


The back-fed 100 amp CB is feeding the bus to left and the one in the center. The jumper feeds the bus on the right. Might not be unsafe except maybe for a violation of its listing. With that arrangement is is possible to overload a neutral if there any MWBC’s that are landed on the B and C phase.

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That part I had figured out. Didn’t think about MWCB’s. Fortunately there weren’t any. It just seemed odd to find this in a 1960’s home. Panel was in good shape. I’m sure it wasn’t original.
The rest of the wiring in home was good

I see 3 at first glance

Yes, 240 volt dedicated circuits. I was assuming he was referring to 120V serving multiple outlets. Am I wrong as far as a potential issue of overloading a neutral at this panel?

If there are no MWBCs then there is no chance of overloading the neutral conductor of an individual circuit as long as the neutral conductor is not smaller than the ungrounded conductors for the circuit. If you are concerned with overloading the service neutral conductor, that should also be fine as long as it’s sized correctly. I, however, would defer such panel for further evaluation because it may not be installed as intended. For that you’d need to find its specs.

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If you had a 240 volt MWBC feeding something like a dryer then you could not overload the neutral if the ungrounded conductors ended up on the B and C phase in this 3Ø panel because your 240 volt circuit would have a line to line voltage of 0. Now if that was a MWBC for (2)-120 volt circuits then indeed the neutral could be overloaded.


If the 100 amp breakers are the main, then there should be a “tie” on there to make it a single throw.


The panel being three-phase does not change the fact that it is still a single-phase system.

The current on the neutral in a MWBC will NEVER carry more than the maximum current one one of the legs. The current on the neutral at any given instant is, for all practical purposes, the difference in the current between the two legs.

The important thing to understand is that the neutral CANNOT be overloaded on a MWBC unless the the circuit is overloaded.

The concern, if any and for the most part, would be feeding a MWBC from the same 120v leg of a single-phase system. In that case the neutral can carry 2x the current. Are you saying a MWBC in a 3-phase panel (wired to a single-phase electrical system) cannot be fed off of the same 120v leg (when miswired/misconfigured via breakers)?

Since you included me in your reply I’m assuming that your comment is in regard to my post. With this installation a neutral can be overloaded if some thinks that they’re running a MWBC when actually they’re not. My post is directed at the fact that this 3Ø panel has the B and C phase bus connected together by a wire jumper. Someone could try to connect a MWBC to the B and C phase bus and overload the neutral.

Two ungrounded conductors on the same leg will not have a potential between them. They will each only have a potential with respect to the grounded conductor.

I responded to the statement you made And that is quoted above.

The B and C busses are connected together. They are, therefore on the same Leg, not different phases. There is ZERO potential between the two busses.

If the panel were, in fact, used on a three-phase system, there would be no jumper connecting the two busses. The three PHASES would be 120° apart from each other. As it is, B and C are 180° Apart from A.

Once again, I will say for the benefit of the person who posted the original questions and for anyone else who is interested in FACTS,


As for who the original poster chooses to believe, one of his choices is a person who has been in the electrical field for 46 years, 39 of which are as a Master Electrician and licensed Electrical/General Contractor, has a Bachelor of Science in Electrical Engineering degree, and has worked as an independent Forensic Electrical Investigator and Inspector for the past 20 years or, he can believe anyone else he chooses to believe.

George you know you’re very good at blowing your own horn.

I’ll say it again, since this is a 3Ø panel and there are 3 different buses, I’ll call them A, B, and C, is it possible for someone to try and connect a MWBC to the B bus and C bus and overload the neutral because they are connected together. We all know that this is fed by a 1Ø, 120/240 volt circuit. The other posters seemed to understand what I was saying.

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What you are failing to understand is that a MWBC CANNOT be connected to the B and C busses because there is ZERO potential between them.

Other may think they understand what you are saying but what you are saying is WRONG. If there is NO POTENTIAL, there is NO MWBC.

Any first year electrical apprentice should know what a multi-wire branch circuit is. On the other hand, I don’t expect a home inspector with no electrical experience to know. They come to forums like this for help and guidance.

There are NON-MEMBERS coming into this forum and posting bad information.

I will blow my own horn if I see people misleading InterNACHI members about matters. An inspector who does not know what a multi-wire branch circuit is, could go out and make a fool of himself if he were to believe the bullshit he reads in this forum.

Are you saying Mike Holt is wrong?

Overloading Of The Grounded (Neutral) Conductor. Failure to properly terminate the ungrounded (hot) conductors to separate phases could cause the grounded (neutral) conductor to become overloaded from excessive neutral current


George is obviously not reading my posts correctly because he insists I’m incorrect which I’m not. I’ll let him have it with his condescending tone. I’ve correctly stated the issue with the panel in the photo’s as others have noted and I’ll leave it at that.

George, you are wrong.

Christopher, It is wrong.

On another related matter, there has been some misleading crap posted in this discussion about multi-wire branch circuits. For your benefit and the benefit of other MEMBERS, I want be sure that you understand that comments about the neutral in a multi-wire branch circuit being overloaded are pure BULLSHIT! IT CANNOT HAPPEN!

I will explain.

A multi-wire branch circuit is one in which there is a potential between the two ungrounded conductors. There is a potential between them because they are on OPPOSITE legs. A multi-wire branch circuit also ALWAYS has a Neutral (Grounded) conductor. The Neutral conductor’s current will always be the difference between between the current in the two ungrounded conductors. Example: Leg A is carrying 10 Amperes and Leg B is carrying 6 Amperes, the difference is 10-6=4. The neutral is carrying FOUR Amperes.

Contrary to what some in this forum believe, two or more conductors on the same leg that are sharing a Neutral do NOT comprise a MULTI-WIRE BRANCH CIRCUIT. Likewise, a 240V circuit with no Neutral serving a 240V load does NOT comprise a MULTI-WIRE BRANCH CIRCUIT.

These guys posting the comments about the neutral being overloaded do NOT know what a multi-wire branch circuit is. If they did, they would know that a MULTI-WIRE BRANCH CIRCUIT does NOT EVER have an overloaded Neutral.

I rarely get on this forum anymore because it is a cesspool of misinformation. You guys, the Members, deserve better.

I would caution any inspector who is looking for ACCURATE electrical information to look elsewhere. When I try to help, I am accused of confusing Members by providing ACCURATE information. When I point out that this is an area where I have considerable expertise, the ignorant among us accuse me of blowing my own horn while continuing to disseminate BULLSHIT!

George, a 2 pole breaker connected to the B and C phase of the pictured panel. Both are on the same 120v leg of the service. Therefore each has a potential to ground of 20A. Now we connect a 12/3 conductor to this. The black wire feeds a receptacle, the red another. Both share the neutral. We plug a 15A load into each receptacle. How many amps are on the neutral conductor?

I understand what you are trying to define with the definition of the term MWBC but in this case it is allbout the window. It is not a proper MWBC and therefore yes, you can overload the neutral. If done properly and by the definition yes correct the neutral carries less current because they are out of phase. That is not what is being debated here from what I can tell. This installation can lead to a hazard an just because you didn’t like how a term was used does not change that fact.