MWBC AFCI Tripping

[ESolar]

New MWBC AFCI (Eaton BRL220CAF) was working fine for a week . The circuit has a microwave, fridge, coffee maker, coffee grinder and Kitchenaid Mixer on it. All were used daily during the past week. The report was that it tripped immediately when the coffee maker was turned on. But only one time, after using all device, including the coffee maker, daily for a week. Nothing else was in use when it tripped (except possibly the fridge). Brand of coffee maker: Cuisinart. No repeat testing because its intermittent, making diagnostics difficult. The Eaton MWBC AFCI breaker has no diagnostic indicators. Coffee maker is plugged into the first outlet (GFCI), although the MWBC branches prior to that in a separate box. Thoughts on trouble shooting?

 

[hbiss]

Try another coffee maker.

-Hal

 

[ramsy]

Read the instruction

https://images.thdstatic.com/catalog/pdfImages/08/08991351-d83c-4974-b8ab-f6d77ea68331.pdf

 

[ESolar]

Read the instruction

https://images.thdstatic.com/catalog/pdfImages/08/08991351-d83c-4974-b8ab-f6d77ea68331.pdf

Eaton never answers when I try. I did not follow the flow charts to the letter. But I can now create a trip. Turns out that they may have been running the microwave. Run fridge, coffee pot, micro, and coffee grinder simultaneously and it trips. They were likely running the micro, coffee pot and fridge (not grinder) - NPRs total 4140W, with grinder 4340W. I suppose that could be it, given the variability in appliances and in the breakers. They have a separate micro circuit that I can easy extend to their current micro location. That might solve the problem.

 

[retirede]

Eaton never answers when I try. I did not follow the flow charts to the letter. But I can now create a trip. Turns out that they may have been running the microwave. Run fridge, coffee pot, micro, and coffee grinder simultaneously and it trips. They were likely running the micro, coffee pot and fridge (not grinder) - NPRs total 4140W, with grinder 4340W. I suppose that could be it, given the variability in appliances and in the breakers. They have a separate micro circuit that I can easy extend to their current micro location. That might solve the problem.

Very unlikely hose loads are balanced across the 2 legs. You only need to overload 1 side to trip the breaker.

 

[LarryFine]

New MWBC AFCI (Eaton BRL220CAF) was working fine for a week . The circuit has a microwave, fridge, coffee maker, coffee grinder and Kitchenaid Mixer on it.

Is all of that on one circuit, or divided between two circuits?

Even then, I would give the fridge and the M/W individual circuits.

 

[ESolar]

Is all of that on one circuit, or divided between two circuits?

Even then, I would give the fridge and the M/W individual circuits.

That was all on one. The micro now has an independent circuit. So now its just a fridge and coffee pot, plus some infrequent appliances. I may be able to easily run a separate fridge circuit. It's only 10 ft. But I don't know if I can fit an AFCI for the fridge in the subpanel.

 

[ramsy]

don't know if I can fit an AFCI for the fridge in the subpanel.

Siemens Type QTA tandem AFCI breakers without the rejection feature can be installed in any panel that lists that breaker type or where a substitution letter exists for that breaker type.

Eaton indicates Non-CTL doesn't have the rejection clip and would be compatible with the BRP.

 

[mtnelect]

With all of these AFCI/GFCI requirements, how can electrical contractors make a living ? You install them, days, weeks and months later, you get a call from the customer that they are not working.

 

[ramsy]

how can electrical contractors make a living ?

In the OP's case, by resolving the typical appliance overload, and billing for it.

If you can't look beyond the flipped panel, you are not a qualified person.

If your contract has no contingency for such interior wiring issues, your bad business is a hazard to the public.

 

[ESolar]

In the OP's case, by resolving the typical appliance overload, and billing for it.

If you can't look beyond the flipped panel, you are not a qualified person.

If your contract has no contingency for such interior wiring issues, your bad business is a hazard to the public.

Another option in this case is to put the fridge on the lighting circuit, which only serves the lights, with a combined draw of less than 1 amp.

 

[ESolar]

Another option in this case is to put the fridge on the lighting circuit, which only serves the lights, with a combined draw of less than 1 amp.

I realize that a fridge cannot share its circuit. The code makers would not allow for it to share with lighting because some lighting loads can be quite high, depending on the lights and whatever else is on the circuit. But in a modern LED lit medium - large 200 sqft kitchen, the lights draw very little. They really should have a calculation, e.g., Fridge NPR + Others < 80% Rated circuit. In this case, a 10.2A fridge + 1A lights < 12A, so 15A would suffice. It beats a SABC micro 6A + coffee 6A + mixer 3A + fridge 10.2A on a 20A circuit, which is allowed but not a good idea.

 

[LarryFine]

The code makers would not allow for it to share with lighting because some lighting loads can be quite high, depending on the lights and whatever else is on the circuit.

I wouldn't want to risk light flicker.

 

[ESolar]

I wouldn't want to risk light flicker.

Good point. But the lights were originally on the SABC without flicker (that I observed). Of course, a new fridge and all bets are off.

 

[ESolar]

We did a little more experimentation with the appliances. The fridge itself is not the issue. The circuit will blow with or without the fridge running and/or starting up. It is the coffee pot + grinder, in combination with an oven (micro or toaster oven). In combo with toaster is OK. And it appears to be overload, but could be arc fault associated with the grinder or coffee pot. The solution is to move the coffee station to the other SABC. At that point in their setup, the fridge is on a MWBC but is the only appliance other than a toaster oven. And the fridge is not the culprit (all trips have been independent) . I get it - its not the fridge - its the fridge on a circuit with something else that can trip it. But I think that we have isolated the problem combination. The new breakers may be set to trip at something like 4250 vs. 4800W.

 

[augie47]

You list a number of appliances on one of the circuits and then note 4800 watts. I'm sure you realize that each of the two circuits you have is only rated 2400 watts... not much considering the appliances that you listed. There's a ton of diversity with those loads cycling but with the heavy hitting
"heat" type loads, a breaker tripping seems a logical reaction.

 

[ESolar]

You list a number of appliances on one of the circuits and then note 4800 watts. I'm sure you realize that each of the two circuits you have is only rated 2400 watts... not much considering the appliances that you listed. There's a ton of diversity with those loads cycling but with the heavy hitting
"heat" type loads, a breaker tripping seems a logical reaction.

Is that correct? Each MWBC circuit is two 20A circuits with tied 20A breakers. Each leg of the MWBC is 20A x 240V = 4800VA. If you load one circuit, your neutral is "maxed out" (in theory but not in practice). If you simultaneously load the other circuit that is out of phase, your neutral load decreases (which is why MWBCs work). From where are you getting 2400VA?

 

[augie47]

Agree that a 20amp MWBC has a capacity of 4800 va, however, you need to look at each individual 120v circuit.
120v @ 20 amps is 2400 va. If a majority of your appliances are on one side of the MWBC, as you seemed to indicate, then that circuit has a limit of 2400 watts. You cold have zero load on 1 phase and once that second phase exceeded 2400 watts you are prone to a breaker trupping.

 

[ESolar]

Agree that a 20amp MWBC has a capacity of 4800 va, however, you need to look at each individual 120v circuit.
120v @ 20 amps is 2400 va. If a majority of your appliances are on one side of the MWBC, as you seemed to indicate, then that circuit has a limit of 2400 watts. You cold have zero load on 1 phase and once that second phase exceeded 2400 watts you are prone to a breaker trupping.

You are correct! Brain fog - as they say. Thank you for pointing out my mistake. And now the tripping makes sense. It was most likely the load and not an arc fault.

 

[ESolar]

Agree that a 20amp MWBC has a capacity of 4800 va, however, you need to look at each individual 120v circuit.
120v @ 20 amps is 2400 va. If a majority of your appliances are on one side of the MWBC, as you seemed to indicate, then that circuit has a limit of 2400 watts. You cold have zero load on 1 phase and once that second phase exceeded 2400 watts you are prone to a breaker trupping.

And that reminds me of another characteristic of the NEC load calcs that has always bothered me. These circuits get 1500VA and then divided by 240V for a 6.25A load in the calcs. I always wondered whether they meant to do that, or if it was an oversight.