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Old 11-02-2019, 09:55 PM   #1
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AFCI Tripping


I have a Siemens subpanel (90A) in my basement that I'm working on. I have three circuits, all 15A (and all recently run), that seem to have nuisance trip problems. It started with a miter saw, which might make sense. Later, a shop vac and then just a regular dyson vac are tripping the circuits.



I've moved the vacuums to all three and it trips them. I have Homelite panel for the main and I've never had the household dyson vac trip those. I've also replaced one of the afci with a regular 15A, and nothing trips.



Could there be a problem with the wiring from the main panel to the subpanel that would cause this? Otherwise, could it just be incompatible breakers? I've checked the wiring to the outlets and everything seems good.
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Old 11-02-2019, 10:13 PM   #2
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Re: AFCI Tripping


Nothing upstream of the subpanel will make breakers trip in the subpanel. The problem has to be in the panel itself or in the circuits that are run from it. It already sounds like you tried multiple AFCI breakers so at least theoretically that rules them out. I would recheck you wiring to all of the circuits 1st. If you don't find anything I would create a new circuit with just a short section of wire (5 feet or so) with a single plug on the end of it. Install it connected to 1 of the breakers in the subpanel and see if things plugged into that temporary circuit trip the breakers.
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Old 11-03-2019, 06:00 AM   #3
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Re: AFCI Tripping


Neutrals tied together somewhere downstream of the breakers?
Neutrals tied to, or in contact with, gnd/bond downstream of the breakers?
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Old 11-03-2019, 07:50 AM   #4
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Re: AFCI Tripping


Staples driven too deep?

Cable clamps too tight?

You mention incompatible breakers. Did you use the type of breakers that are listed on the sub-panel?
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Old 11-03-2019, 09:13 AM   #5
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Have you tried using the devices on other AFCI protected circuits in another panel? Do other devices trip the afore mentioned circuits? Could be these motors are not suitable for AFCI circuits.
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Old 11-03-2019, 12:42 PM   #6
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Nuisance tripping had been an issue for years...AFCI breakers don't like motors...my shop-vac will trip the one in my garage.
One problem is that the spec on these breakers is 5mA max...there is no minimum...so breaker manufacturers are free to make them more sensitive to pass the spec.
The AFCI breaker compares the current in the hot to the current in the neutral line...if it's off by 5mA or more, it trips. But as I stated, yours may be more sensitive.
Motors can be a problem as the initial inrush of current will "charge up" the large inductor and the returning current may not match the current in the hot line.
Large capacitive loads will have the same effect.
It may be just the motors...or as stated above, you may have multiple return paths...or there is a leakage path to ground somewhere.
If other devices work such as lamps, the circuitry is likely ok.
If your devices are double insulated (no exposed metal), and you're not in a wet area (not worried about getting shocked), use a ground lifting plug...a motor may still trip the breaker, but at least you will have narrowed it down to the motor or just a very sensitive breaker...
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Old 11-03-2019, 02:00 PM   #7
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Re: AFCI Tripping


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Originally Posted by zhawkeye View Post
Nuisance tripping had been an issue for years...AFCI breakers don't like motors...my shop-vac will trip the one in my garage.
One problem is that the spec on these breakers is 5mA max...there is no minimum...so breaker manufacturers are free to make them more sensitive to pass the spec.
The AFCI breaker compares the current in the hot to the current in the neutral line...if it's off by 5mA or more, it trips. But as I stated, yours may be more sensitive.
Motors can be a problem as the initial inrush of current will "charge up" the large inductor and the returning current may not match the current in the hot line.
Large capacitive loads will have the same effect.
It may be just the motors...or as stated above, you may have multiple return paths...or there is a leakage path to ground somewhere.
If other devices work such as lamps, the circuitry is likely ok.
If your devices are double insulated (no exposed metal), and you're not in a wet area (not worried about getting shocked), use a ground lifting plug...a motor may still trip the breaker, but at least you will have narrowed it down to the motor or just a very sensitive breaker...
You're describing GFCI functions - the problem here is AFCI - Arc Fault Circuit Interrupter- AFCIs trip when detecting the electrical signature common to electrical arcs.
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Old 11-04-2019, 09:15 AM   #8
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Re: AFCI Tripping


You're right...I blew right past that...sorry, I'm dealing with GFCI problems with our products at work, so I've got GFCI on the brain at the moment...
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Old 11-04-2019, 01:32 PM   #9
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Re: AFCI Tripping


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Originally Posted by zhawkeye View Post
You're right...I blew right past that...sorry, I'm dealing with GFCI problems with our products at work, so I've got GFCI on the brain at the moment...


GFCI are highly reliable now. Your suggestion manufacturers make them too sensitive is plain wrong.

If you are having trip problem look for a leakage current to ground creating an in balance of the hot and neutral.


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Old 11-05-2019, 07:21 AM   #10
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Experimenting with different GFCI breakers give us different results. Our issue is that we use switching power supplies instead of the older style linear supplies...switching supplies inherently have leakage to ground...that's how they filter out the RF noise generated by the switching circuitry.
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Old 11-06-2019, 06:16 AM   #11
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Re: AFCI Tripping


RetroActv is stating that they are AFCI breakers not GFCI breakers.


RetroActv: are you sure they are AFCI breakers and not GFCI breakers.


If so then try switching the wires from the AFCI breaker that is tripping to another AFCI breaker in the panel. If the breaker trips again at least you know it is not the breaker that is faulty.


Again, AFCI (CAFCI) breakers monitor the circuit for "C.ombination" A.rc F.aults which means arcs in series or parallel. Thus the term combination. Some people confused the term in this case "combination" meaning the breaker is both AFCI and GFCI. A breaker that is both AFCI and GFCI is called a "Dual" purpose not a "combination". GFCIs and AFCIs monitor two totally different types of faults.
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