attic fan trips afci

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cjmeyer

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I had an attic ventilator fan on a circuit that was moved to an AFCI over the winter. Now that the warm weather is finally coming around, I found every time the fan tried to go on, the AFCI tripped. Is this to be expected for a 3-4 amp motor ?
 
Re: attic fan trips afci

An AFCI also has a 30 to 50 mA GFP circuit. You may have a ground fault in the motor, or a inadvertant neutral to ground connection.
 
Re: attic fan trips afci

How far away from the panel is the attic fan? Ive been having problems in larger homes with false tripping if the load is too far away from the source. So Ive actually started running #10 to alot of my AFCI circuits if they are far away.
 
Re: attic fan trips afci

It's old an old multi-room romex 14 awg circuit. The fan is about 70 ft from the AFCI. I isolated the other stuff (lights, etc) off the circuit when I was trying to determine what was tripping the AFCI.

It's presently working fine on a standard breaker. I'm planning to check the fan for an isolated neutral, but otherwise, I don't know why the AFCI tripped.

The fan is a standard type attic vent fan drawing about 3 amps.
 
Re: attic fan trips afci

The UL test for an AFCI uses an air compressor with about 148 amperes locked rotor current to test for motor loads, if I recall correctly from a recent Mike Holt newsletter.
I suspect the AFCI is operating properly, you have a problem in the wiring to the fan or the fan. Can you get to the junction box for the fan and check it?
Interesting comment on using 10 AWG for a home run for an AFCI ckt....
 
Re: attic fan trips afci

A capacitor, across the load, will fool the AFCI into thinking it is an arc.

Capacitance coupling, in the 70 feet of wire, may be initiating the trip.

Disconnect the leads at the motor. Check to see if the AFCI still trips.

If it still trips, the remedy is knob and tube wiring method to reduce the coupling :D

[ April 30, 2003, 12:18 PM: Message edited by: bennie ]
 
Re: attic fan trips afci

Make sure your circuit isn't daisy-chained through a bunch of receptacle "stabs" before it gets to the fan. My experience has been motor loads will trip an AFCI if these nasty nasty stab-locks are utilized.
 
Re: attic fan trips afci

Are you sure it is triping when it goes on and not off. I have found that some motor loads will trip a gfi when turning off. When it is coming to a stop after power is taken away it runs like a generator and will send voltage back on the netural. I have cured this with two pole swithes.
That might be hard to do with a attic fan.
afci have 50 ma gfi
 
Re: attic fan trips afci

Since the start of afci requirement we have found that when the rough in is done and a bathroom was included in this circuit the bath exhaust fan was causing the afci to trip.Since we do at least 2000
homes a year this was causing a flood of call backs for the service dept.As a result we now feed the bathrooms from a circuit that is not an afci circuit and the call backs on these homes is almost nill.
 
Re: attic fan trips afci

Ok, so I'm not the only one seeing fans trip AFCIs. Anyone able to explain what's going on ?

By the way - it trips when the fan tries to go on, not off. Also, AFCI is wired correctly, the fan does not have a ground fault, and it was passing through only about two or three stabs.
 
Re: attic fan trips afci

If everything is wired correctly...the circuit will trip with too much inductance or capacitance anywhere along the cable run from the hot back thru the neutral.
The 'Ground Fault' is sensed by a difference in current measure between the hot side supply and what is comming back from the load. The trip point of 50mAmps is the difference between what is going to the load and what is comming back from the load. In inductive loads such as the usual fan motor, the load current measured at the motor dosen't really get there untill after the voltage does( to the GFC it first looks like an open and then a dead short untill the motor gets running fast enough to nill the effect. Vice Versa; capacitive loads are the oppisite, first they look like a dead shorts then an open circuit.
A capacitor accross the hot and neutral input leads to the fan will (Even)out the current and voltage. Because cost is a driving factor in the market...no manufacturer will want to spend the extra 6 pennies per motor on a capacitor, they weren't needed untill you might have been required to install a GFC type device by code.You should be able to contact the fan OEM and ask them for the correct value of part to use. If they can't there engineer should be fired and I wouldn't but anything from them anymore. But that and everything else is just my personal opinion!
 
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