What's wrong with this breaker?

The person who wired it is to blame. The circuit would be OK if he had used a two pole breaker with a tie bar. That single pole tandem breaker cannot be used for a MWBC because there is no voltage between the two ungrounded conductors. To fix it one would change out the breaker.

Per NEC

Chuck I understand the issues. But my question for you is how do you write them up?

What about the cutler hammer breaker at the bottom?

Here is what went into the report.

The one I mentioned in the initial post? What about it?

Sorry Chuck.

I scanned that post a bit too fast and concentrated on the picture. oops

There is a LOT of information about this exact issue on the internet, like Chuck said, it is a very important concern many folks may overlook.

Good post Chuck…!

With all due respect, there is is not enough of the panel visible to be certain just from your photo that is a MWBC.

That said, excellent topic and a good example of how it takes more than a passing glance to properly evaluate an electrical panel. I also appreciate you providing your report comment. Fun topic and good brain food.

This type of breaker (when used in a MWBC or “shared neutral”) can draw too much current through the neutral.

The breaker provides two separate circuits with up to 15 amps of current on a single “phase” of 120V. That’s a potential load of up to 30A on a small neutral conductor before the breakers would trip, which would result in melting of the neutral conductor - a fire hazard.

When placed on opposite legs of 120V (alternating current), the neutral would not carry more than its design-load up to a point where the breaker would trip.

This setup would have been better suited for a standard breaker with a saddle fitting that allows more than one conductor. There would be a potential for “nuisance tripping,” but less opportunity to overload the neutral.

Generally, the MWBC’s of kitchens are circuits that do not require GFCI protection, such as the disposal and dishwasher circuit.

In addition, the circuits that require GFCI protection will generally be the 20 amp, small appliance branch circuits for counter top receptacles. In most cases, these will be protected at the receptacle, rather than at the breaker.

Good thread Chuck.

I understand all that has been said but…

  1. How did you determine that the red and black conductors connected to this OCPD were configured as a MWBC?

  2. If you are using I/R to detect an overloaded shared neutral on a MWBC, does that not presuppose that you have placed a load of more than 15 amps on the circuit in question? How do you go about this? Do you load each circuit in the home in this manner in order to observe the thermal results within the main panel?

Just trying to learn.

I think this is what some call a half breaker and they are fed from a single phase .so two on phase B overloads the neutral

There needs to be more posts like this. Thanks for posting

But who is to say that those red and black comductors share the same neutral? This can not be determined from the photo. Many panels are so full that it is not possible to trace the conductors even back to the sheathing. Even if you could, that does not guarantee that the red and black are being used in a MWBC configuration at the other end.

That’s what NACHI is all about ,
We have many who try to help when when the know the answer.

I would like to take the time to thank Chuck and all for this post, excellent topic of discussion.

I am posting a panel from yesterdays inspection. The branch wiring in the basement was a mess. I had trouble following portions of the wiring in the panel. It looks like one(or more) of the [MWBC]] is on to separate circuits in the panel.

I would like to ask of your opinions on the electrical panel. Not sure if you can see from the picture.

Thanks again Chuck!! Nice work!!

I am getting my code check illustrations in a few days and If I see one that pertains to this topic I will post.

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  1. We must presume that Chuck was able to verify this by following the conductors entering the panel. It is not visible in the photo.

  2. In most cases, those of us who incorporate TI in our inspections (including me) will apply normal loads to branch circuits before checking the service equipment.

Even under normal loads, the neutrals in these types of circuits will often indicate “higher than normal” temperatures. In extreme cases, the neutral will already be charred or burnt.

Unless it is 220/240 then only one neutral would indicate a MWBC or a 230/240 which is not properly in tandem. You are correct the photo doesn’t fully show this and it may not be fully visible in a crowded panel.

Your photo does not give enough detail to see what’s going on. Do you have any better pictures?

I defiantly look for overheated neutrals but most MWBC are receptacles, you guys arn’t loading receptacles are you?

I am trying to learn from others with more experience than myself, just want to make sure you are understanding the tone of my posts. I am putting my I/R camera to good use but not for electrical yet.

No I have no up close pics, I wish I did, I do have a lot of pics of the non professional wiring.

Thanks again for the educational posts, please create more!!