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# Electric breaker thresholds and AFCI thresholds

## Electric breaker thresholds and AFCI thresholds

#1
02-28-11, 03:25 PM
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Electric breaker thresholds and AFCI thresholds

What's the threshold for a 15 amp breaker? For almost two years my 12a vacuum never had an issue on our 15a circuit but yesterday the circuit tripped twice. The only other items on the circuit were 5 CFL lights with an aggregate of 60w.

Is 12a the max current the vacuum with draw? or the average it draws?

I'm also noticing the breaker is tripping more since I swapped it with an AFCI. Do AFCI have lower thresholds?

Trying to gauge if I should be concerned since the wiring is about 50 years old. The circuit only trips under a load.

#2
02-28-11, 03:35 PM
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One of the pros will come along and correct me if I'm wrong, but an AFCI will trip QUICKER than a normal breaker. Your 12A vacuum will draw it's max amps upon start up, and that's what the AFCI is sensing. If all of the CFL's are off, it may or may not trip the breaker on start up of the vacuum. With 4 or 5 of them on, it probably will.

#3
02-28-11, 03:43 PM
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The load would be 120v * 12a + 60w = 1500w or about 12.5a

So around 80% is the threshold?

#4
02-28-11, 03:57 PM
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The trip threshold of a 15A breaker should be about 15A, although they are mechanical devices so some variation is to be expected. Tripping on only 12A would be unusual (assuming you actually measured current with amp meter).

Your vacuum's rating should be the maximum current under normal conditions. If the vacuum is malfunctioning (clogged bag, bad motor, shorted switch) it may be drawing more. Does the vacuum trip the breaker immediately when you switch it on or after a period of running?

AFCI breakers additionally have a microprocessor that can detect when there is sparking in the wiring in the circuit such as would be caused by frayed cords or loose connections. They do occasionally have false trips, but it could be an intermittent problem in your wiring or vacuum cleaner.

#5
02-28-11, 04:16 PM
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Originally Posted by ibpooks
Does the vacuum trip the breaker immediately when you switch it on or after a period of running?
First time it tripped after a minute. The second time after about 10 seconds.

#6
02-28-11, 04:42 PM
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AFCI breakers do not trip quicker than a "normal" breaker. As Ibpooks mentioned, they do the additional components for detecting arcing. As far as overcurrent goes, they should react the same as a normal breaker.

Circuit breaker ratings are not an exact thing, they have a tolerance. A 15 amp breaker can hold beyond 15 amps for a length of time before tripping. Breakers do wear out but you may have some other "unknown" load on the circuit. I suggest trying the vacuum on another circuit and see if you get the same result.

First time it tripped after a minute. The second time after about 10 seconds.
Breakers trip due to heat. that could be why it tripped faster the 2nd time.

#7
03-01-11, 10:10 AM
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Would the arcing of the motor's brushes cause the AFCI to cut out? It would seem to me that this is potentially an irritating side effect of AFCI's when a motor load is placed in the circuit it protects.

#8
03-01-11, 10:55 AM
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I suppose the brushes could cause a trip when they are getting worn out. The AFCI is designed to allow brushed motors in good condition to run without tripping the breaker. The microprocessor in the AFCI monitors for very specific patterns that are observed in frayed cords.

#9
03-01-11, 11:45 AM
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No one has mentioned failing breaker yet. I know being AFCI it is probably not that old but if you have another AFCI of the same size in the panel I'd suggest swapping the hots to them and see if you still have the problem.

#10
03-02-11, 02:57 AM
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Originally Posted by ray2047
No one has mentioned failing breaker yet. I know being AFCI it is probably not that old but if you have another AFCI of the same size in the panel I'd suggest swapping the hots to them and see if you still have the problem.
Don't do that Ray., The reason why you need matched hot and netural to function properly.

And there is other trick I done from time to time first thing first is unhook the hot conductor from the AFCI breaker and test it to see if that hold on it own if not then you have bad breaker if hold on {stay on } then what I do is swap either other working AFCI breaker or get a GFCI breaker and test it NOTE:: Only for testing purpose if that trip out then you have issue with conneciton somewhere along the circuit.

to OP I do not know what namebrand the breaker you have in your load centre I know couple earliers one they have some quirks but the latter one is better than old one so if you can tell us that will help a bit with it.

Merci.
Marc