Thread: Unexpected tripping of AFCI

I have inspected two houses where in both cases electric powered brand new exercise equipment (treadmills) caused the main panel 20 amp AFCI breaker to trip. In both of the cases these were bedroom circuits that had only minimal electrical load, meaning maybe an alarm clock or lamp were in use in addition to the treadmill. Doe this represent a malfunction of the AFCI? or an expected reaction? I would think the microchip inside the AFCI would be programed for a different sort of electrical signature than a simple surge. Has anyone else seen this?

Gene,
More than likely the installation instructions for the treadmill state that the device should be on a dedicated circuit. Usually, it's the motor start-up causing the problem.

Originally Posted by Gene South

I have inspected two houses where in both cases electric powered brand new exercise equipment (treadmills) caused the main panel 20 amp AFCI breaker to trip. In both of the cases these were bedroom circuits that had only minimal electrical load, meaning maybe an alarm clock or lamp were in use in addition to the treadmill. Doe this represent a malfunction of the AFCI? or an expected reaction? I would think the microchip inside the AFCI would be programed for a different sort of electrical signature than a simple surge. Has anyone else seen this?

It is very, very common for electricians to get calls for treadmills, televisions, computer power supplies and vacuum cleaners tripping AFCIs. All of these devices produce a harmonic and wave form distortion (current ripple) that can trip AFCIs. Manufacturers are intensely working on improving AFCIs that are not affected by these appliances but yet can still detect an abnormal current condition caused by an arc fault. Its a difficult task to pull off especially when manufactures are trying to keep AFCI prices economical by using simple logic circuits. Since an arc fault caused by a nail in a wire and the arc between the brushes of a running vacuum cleaner motor produce similar current signatures it takes time for the manufacturers to iron out all the bugs.

Another possibility is a neutral to ground fault. Most AFCIs will trip on a neutral to ground fault when load starts to be applied. Less likely but neutral to ground fault do occur and do trip AFCIs.

In both cases an electrician would need test for a neutral to ground fault and if ok would need to put in a newer version AFCIs. Manufacturers are always coming out with newer versions of AFCIs for the exact reason older ones have trouble telling a dangerous arc fault and a running vacuum cleaner/treadmill apart.

Originally Posted by Donald Farrell

Gene,
More than likely the installation instructions for the treadmill state that the device should be on a dedicated circuit. Usually, it's the motor start-up causing the problem.

Hi Don, yes, the start-up surge is causing the AFCI to trip. I spoke with an electrician today. He told me treadmills are notorious for causing AFCI's to trip. But that doesn't make it right however.

- - - Updated - - -

Originally Posted by Gene South

Hi Don, yes, the start-up surge is causing the AFCI to trip. I spoke with an electrician today. He told me treadmills are notorious for causing AFCI's to trip. But that doesn't make it right however.

Maybe a new AFCI breaker would not be so sensitive. Thanks for your input.

Gene

Originally Posted by Donald Farrell

Gene,
More than likely the installation instructions for the treadmill state that the device should be on a dedicated circuit. Usually, it's the motor start-up causing the problem.

Even a dedicated circuit receptacle in a bedroom, or basically any other room too, the receptacle would be required to be AFCI protected if not GFCI protected (there are limited exceptions, but by and large the circuits will either be AFCI protected or the receptacles GFCI protected).

Originally Posted by Jerry Peck

Even a dedicated circuit receptacle in a bedroom, or basically any other room too, the receptacle would be required to be AFCI protected if not GFCI protected (there are limited exceptions, but by and large the circuits will either be AFCI protected or the receptacles GFCI protected).

Ok clarify your reply please

Are you saying it needs to be one or the other? (AFCI OR GFCI ?)

Originally Posted by jack davenport

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Ok clarify your reply please

Are you saying it needs to be one or the other? (AFCI OR GFCI ?)

AFCI protected.

Originally Posted by Donald Farrell

AFCI protected.

Oh I know what it should be, but Jerry's reply is kinda written in circles or my mind is warped tonight ( which is a possibility )

Originally Posted by jack davenport

Oh I know what it should be, but Jerry's reply is kinda written in circles or my mind is warped tonight ( which is a possibility )

Jack,

What I'm saying is, that depending on which room the treadmill is plugged in will depend on what type of protection the receptacle will have.

Additionally, I am also saying that (basically) unless the treadmill is plugged into a receptacle in a location which requires GFCI protect, the treadmill will be plugged into a receptacle which has AFCI protection.

In other words, regardless where the suggested dedicated circuit is or where it goes to, either the receptacle will require GFCI protection (garage, kitchen, bathroom, etc) or the circuit will require AFCI protection (bedroom, living room, family room, den, etc).

There are very few receptacles in a house which will be on a circuit which does not have AFCI protection, and almost all of those receptacles not having AFCI protection will have GFCI protection. So, almost regardless where the treadmill is plugged in it will have AFCI protection on the circuit supplying the receptacle - if the treadmill is causing the AFCI to trip, adding a dedicated circuit will not solve that problem.

However, if the treadmill is tripping a 20 amp breaker to a bedroom circuit, unless the treadmill is drawing well over 20 amps at start up surge (which I doubt) the 20 amp breaker should not trip on overcurrent - especially when "In both of the cases these were bedroom circuits that had only minimal electrical load, meaning maybe an alarm clock or lamp were in use in addition to the treadmill."

That leaves the 20 amp AFCI breaker tripping because of the AFCI function "Doe this represent a malfunction of the AFCI? or an expected reaction? I would think the microchip inside the AFCI would be programed for a different sort of electrical signature than a simple surge."

If the treadmill trips the AFCI function of the breaker, the first thing I would check (presuming that the rating of the treadmill has been checked and that it is not tripping the overcurrent function of the breaker) would be to replace the breaker just in case there is there was a problem with the first breaker. If the replacement AFCI breaker trips too, then I would next check it by replacing - temporarily replacing - the AFCI breaker with a non-AFCI breaker. If the problem is still present, it is likely overcurrent tripping the breaker, if the problem is no longer present, then the problem is either a problem with the circuit (don't forget to remove the non-AFCI breaker and reinstall one of the AFCI breakers)) or there is a problem with the equipment.

There could be a problem with the circuit which is causing the AFCI to trip with a heavy load on the circuit but not trip with almost no load on the circuit. Of, the problem could also be the treadmill itself - in which case I would wonder if the two treadmills were the same brand ...

Not sure if that helped clear up what I was saying or if I muddied the water even more?

Dimmer switches have also been known to cause AFCIs to trip. some newer models have solves this problem. The first thing I would check is whether the manufacturer has a revised model of AFCI.

I find it interesting that a bedroom circuit has a 20 amp breaker. All of the bedrooms in my house are on 15 amp circuits. In fact the only 20 amp circuit that I have is for the kitchen and for the outdoor Christmas lighting.

Is it just me?

15 amp is the norm here. The max receptacles and fixtures on a 15 amp circuit is 12, per the Canadian CEC.
In Canada, 20 amp kitchen counter outlets became acceptable in 2006. Before that they had to be 15 amp split duplex, which is still allowed but we need GFCI's either side of the sink. The 20 amp non-split circuit makes that easier than having to install double 15 amp GFCI breakers in the panel..

We are required to have AFCI on bedroom circuits. That's it, one or 2 15 amp AFCI breakers just for the bedrooms receptacles.The bedroom lights can be either on AFCI or not.
Are we all getting shocked to death? Not that I know of.