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We have a problem with a 15A breaker repeatedly tripping. This circuit seems to be servicing the thermostat, and could possibly power the blower motor. It will work fine for a few hours, maybe even a day or so, but then randomly the breaker will trip. Last winter we had the glow plug replaced for the heater, and the service tech mentioned something to me about the blower motor making noise and possibly going out, like the bearings might be beginning to fail. I haven't found any other power draw on that circuit that would cause an overload.

Could the motor failing be the cause of the overload?

What is the likelihood that both the blower and the thermostat are on the same circuit?

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  • Other than furnace equipment, what else is on that circuit?
    – Harper - Reinstate Monica
    Jun 27, 2017 at 20:58
  • Did you see my answer located at "Safe to test circuit breaker is working by overloading it"? ask yesterday by @Joe. You'll never know the problem until you check the amperage draw.
    – Retired Master Electrician
    Jun 28, 2017 at 0:25

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Could the motor failing be the cause of the overload?

Normally, there is an overload fuse or breaker on the air handler / evaporator that protects the motor at more like 3 amps. This is supposed trip if the motor is overloaded. The 15 amp breaker is supposed to protect the conductors to the air handler / evaporator.

What is the likelihood that both the blower and the thermostat are on the same circuit?

Yes. The thermostat is actually 24volt on the secondary side of a 120volt to 24 volt transformer fed by the 15 amp circuit.

If the breaker keeps tripping that is telling you something is broke.

Call a reputable HVAC or electrical contractor to take a look at it.

Good luck!

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Try oiling the motor (if it has oiling ports on it) or spraying both ends with a penetrating lube. I'd say it could cause the circuit to trip when starting up if it's requiring more than the normal amount of juice to overcome a sticking spot in the bearing. Which might explain the randomness of it as it may only happen when trying to start at only one particular spot in the 360 degrees of possible rotation. I'd spray the bearings first and see if that keeps it from tripping and if so then time for a new motor or get it rebuilt by an electric motor or alternator rebuild type place. If that's not it then it might be time for an electrician to go over your service panel and all the connections to make sure everything is tight and how it's supposed to be.

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    Be careful what you spray on the motor. If the lubricant is volatile, then fumes will be swept onto the evaporator coils (and if there is a furnace, onto the walls of the heat exchanger) and into the duct work. You will smell it throughout the house, maybe for a long time.
    – Jim Stewart
    Jun 27, 2017 at 17:48

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