Ground fault and AFCI 2-pole breaker

[kolodziej_m]

2 hot wires of different phases are sharing a neutral. The 2 circuit breakers are off and the neutral has a ground fault with voltage. When the 2 circuit breakers are on breakers don't trip. When a AFCI is used the circuit fries the breaker.

 

[James L]

You need to clarify what you are asking.

In the thread title you mention AFCI 2-pole breaker, then 2 times in the description you mention 2 circuit breakers. Which is it? Is it one circuit breaker or two?

When you say there is a ground fault with voltage, what exactly are you saying? Are you reading voltage from the load lug of the AFCI breaker to the neutral bar? Or did you unhook the neutral altogether and read voltage from that to the neutral bar? Not that it matters in that regard, but just what are you getting at?

How many volts do you have on that neutral when the hots are turned off? What's the circuit supposed to be powering?


Nonetheless, my first guess is that something might be sharing that neutral when it's not supposed to be. I would put a voltage tester on it, and turn off all other breakers one at a time until the voltage goes away. Then you've found which circuit is dropping voltage onto that neutral.

But I'm going with the assumption that I understand what you're saying, when I might not. Clarify, please

 

[GoldDigger]

"When an AFCI is used the circuit fries the breaker."
That sounds like the breaker is being back fed when off, leading to a shunt trip type coil carrying a constant current rather than a momentary current.
I suspect that this is not a normal MWBC but instead has another breaker supplying power to the circuit when both of the supposed supply breakers are open.
There may be a compromised neutral involved too, but that is hard to tell from the confusing description.

 

[kolodziej_m]

The 2 existing breakers were 15a Siemens. I replaced those 2 with the 2 pole AFCI. When the AFCI fried I disconnected it and felt a shock from neutral. I measured the neutral wire to the neutral bus and the voltage was 120v. I started shutting off breakers until neutral was 0v. I had to have 6 breakers off until neutral was 0v. I am currently going from outlets, switches and lighting fixtures in the process of elimination. I am currently at: a bedroom light fixture with a hot neutral; a hall light with a hot neutral; a combination switch at the foyer with 2 hot neutrals. When I go back I'm going to shor

 

[kolodziej_m]

The 2 existing breakers were 15a Siemens. I replaced those 2 with the 2 pole AFCI. When the AFCI fried I disconnected it and felt a shock from neutral. I measured the neutral wire to the neutral bus and the voltage was 120v. I started shutting off breakers until neutral was 0v. I had to have 6 breakers off until neutral was 0v. I am currently going from outlets, switches and lighting fixtures in the process of elimination. I am currently at: a bedroom light fixture with a hot neutral; a hall light with a hot neutral; a combination switch at the foyer with 2 hot neutrals. When I go back I'm going to short out each location hopefully tripping a single breaker.

 

[John120/240]

................................................................................................................................................................................................................................................. When I go back I'm going to short out each location hopefully tripping a single breaker.

PLEASE DON'T. Invest in a circuit tracer or one guy in the bedroom watching the light, second guy at the panel turning breakers off one at a time.

ps how do you make red text or bold

 

[GoldDigger]

In the advanced formatting bar the capital letter A is the button for changing the font color for the selected text.
Or you can look at the result and just type in the appropriate HTML tags for the color you want.

 

[James L]

The 2 existing breakers were 15a Siemens. I replaced those 2 with the 2 pole AFCI. When the AFCI fried I disconnected it and felt a shock from neutral. I measured the neutral wire to the neutral bus and the voltage was 120v.

Now we're getting somewhere.

I started shutting off breakers until neutral was 0v. I had to have 6 breakers off until neutral was 0v.

This one right here. When you turned off the 6th breaker, and voltage went to zero, did you tyrn the other 5 back on?
If you did turn them back on, did you check the voltage on that neutral each time you turnd a breaker on?

Hard to imagine you have six different circuits giving you voltage on one neutral. I would bet it's only the 6th one, and not the first 5

I am currently going from outlets, switches and lighting fixtures in the process of elimination. I am currently at: a bedroom light fixture with a hot neutral; a hall light with a hot neutral; a combination switch at the foyer with 2 hot neutrals. When I go back I'm going to short out each location hopefully tripping a single breaker.

It sounds like you might have a box that has two different circuits in it, and the neutrals are tied together wrong. Possibly a multi-gang switch box that has 3-way traveler cable carrying the neutral with it, tied in wrong where it's sharing a box with switches on different circuits.

By the way, this 3-wire circuit you're looking at....what is it supposed to be powering? Is it lighting general use plugs?

Have you tried:
Go to the panel and land that crazy neutral into the neutral bar, and put an amp meter on it. Make absolutely sure which ONE circuit is misusing that neutral, and look for openings on that circuit that would account for the amperage on that neutral

 

[GoldDigger]

I still think that the "fried" breaker would have to result from a stray voltage on the ungrounded conductor OR the neutral pigtail from the breaker not being solidly landed, allowing the neutral terminal of the breaker to provide power through the trip coil of the breaker to the ungrounded conductor(s).

 

[ActionDave]

I still think that the "fried" breaker would have to result from a stray voltage on the ungrounded conductor OR the neutral pigtail from the breaker not being solidly landed, allowing the neutral terminal of the breaker to provide power through the trip coil of the breaker to the ungrounded conductor(s).

I'm going over the wall with you, or through the hedge if that is a better metaphor....

If there is some existing wiring that is not up to par and a two pole afci is added and on top of that the wrong neutral on a MWBC was opened something would get fried.

If I plow through all of the info and ignore any technical jargon that crosses over into slang my best answer is there is a bootleg neutral somewhere.

 

[ActionDave]

The 2 existing breakers were 15a Siemens. I replaced those 2 with the 2 pole AFCI.

What was the reason for doing this?

When the AFCI fried

Please add some detail. Did smoke come out of the AFCI breaker? Did it happen in front of you when you turned the breaker on?

I disconnected it and felt a shock from neutral.

Disconnected it how?

I measured the neutral wire to the neutral bus and the voltage was 120v. I started shutting off breakers until neutral was 0v. I had to have 6 breakers off until neutral was 0v.

Which neutral wire? The wire from the circuit that lands on the breaker or the wire from the breaker to the neutral buss?

I am currently going from outlets, switches and lighting fixtures in the process of elimination. I am currently at: a bedroom light fixture with a hot neutral; a hall light with a hot neutral; a combination switch at the foyer with 2 hot neutrals.

Are all the neutrals fed from the same circuit or at least supposed to be? Could there be a box somewhere that has more than one home run or power from another circuit in it with all the neutrals tied together?

When I go back I'm going to short out each location hopefully tripping a single breaker.

Not the best plan.

 

[kolodziej_m]

Hot neutral

Hot neutral

When I turn off the 2 breakers sharing the hot neutral the neutral = 0v. I disconnected the 3 way switches then turned the 2 breakers on. Neutral once again is hot.

 

[James L]

When I turn off the 2 breakers sharing the hot neutral the neutral = 0v. I disconnected the 3 way switches then turned the 2 breakers on. Neutral once again is hot.

That doesn't sound like the scenario you first mentioned.

You need to get real specific on what you're doing. And you need to answer the questions people ask you.

What do you mean that you disconnected the 3-way switches? Did you just take the common and travelers off the switch, or did you unhook all the neutrals and grounds, too?

Twice, you've been asked what this 2-pole circuit is powering

We're guessing that it's lighting, but if you want help you're going to have to help us get a better handle on the scenario.

I mentioned the possibility that you have a multi gang box with a 3-way switch in it, with neutrals connected wrong. And now you mention 3-way switches

Whether you've got neutrals from 2 circuits swapped, which is my hunch, or if you have neutrals from 2 circuits all hooked together (what ActionDave proposed)......

If you want help, you need to follow instructions you're being given, and then report back EXACTLY what you did and the result of it.