Air Handler Breaker Tripping

[Sean B]

Residential HVAC system. Air handler in attic of a ranch home. Heat pump. Outdoor unit.
Having a problem with the air handler circuit.

There is one feed to the air handler - a #6 AWG 2-wire copper feed with ground. 60 ampere square D breaker in distribution panel in garage. Another 60 ampere square D breaker at the air handler in the attic. It's a Carrier system.

The circuit goes to a small transformer in the air handler and runs a blower motor. I have tested the current on both conductors while the blower motor is running. The current is about 5 amperes on each leg which seems about right for this little motor.

In the winter, if the heat pump can't do the job (Pennsylvania) there is a 10 kW 2-stage resistance-heat element that kicks in.

I have never had any problems with the resistance heat running in the winter with a current of a little over 40 amperes on the circuit.

The mystery is that in the summer, with only the fan running, I have had a few occasions where the 60 ampere breaker in the attic is tripping. The out-door unit is a separate 30 ampere 240V circuit so it is not involved.

Any thoughts on why this breaker is tripping under a 5-ampere load? I checked connections, no loose connections, no evidence of shorts, the motor turns freely and no smell of burned varnish or anything else. The only factor I can think of is that it happens when it is about 100+ degrees F in the attic.
Everything looks clean around the motor and fan. Replace filters often.

Could the high temperature cause the breaker to trip at such a low current? I believe the system was installed about 20 years ago.

Any help is appreciated. I am considering a new breaker for the attic unit but didn't want to spend 100 dollars unless I have to.

 

[Jraef]

High ambient could indeed cause a breaker to trip. the trip element is just a bi-metal strip, just like a cheap thermostat, so it reacts to heat no matter what the source is.

That said, 100 deg. F is not that hot. But is that the outside air temp or the temperature in the attic? If there is no venting in the attic and the sun is beating down on the roof, the temperature inside of that carrier unit could be a lot higher than the outside air temp and once a breaker starts repeatedly tripping, it starts to take less and less to make it trip again.

 

[growler]

I have had a few occasions where the 60 ampere breaker in the attic is tripping. I am considering a new breaker for the attic unit but didn't want to spend 100 dollars unless I have to.

What type of breaker does it have in there. Most 2 pole 60 amp breakers are a lot less than $100.00.

Jraef is right and a breaker could trip because of external heat but there are lots of breakers in lots of attics that are not tripping. Normally they trip because of heat when the are already near the tripping point of current draw. Did you check the breaker to see how hot it gets once the unit has run for awhile ?

 

[Sean B]

The breaker is a feed-through square D model QOU2605258 240 VAC.

I need to measure the temperature on a hot day but it is very, very warm up there. For a guess, 140F. The breaker is ambient temperature. Doesn't feel warmer than any other surfaces in that area. The breaker in the garage is relatively cool, around 75 to 80 degrees F and has never tripped.

 

[GerryB]

Residential HVAC system. Air handler in attic of a ranch home. Heat pump. Outdoor unit.
Having a problem with the air handler circuit.

There is one feed to the air handler - a #6 AWG 2-wire copper feed with ground. 60 ampere square D breaker in distribution panel in garage. Another 60 ampere square D breaker at the air handler in the attic. It's a Carrier system.

The circuit goes to a small transformer in the air handler and runs a blower motor. I have tested the current on both conductors while the blower motor is running. The current is about 5 amperes on each leg which seems about right for this little motor.

In the winter, if the heat pump can't do the job (Pennsylvania) there is a 10 kW 2-stage resistance-heat element that kicks in.

I have never had any problems with the resistance heat running in the winter with a current of a little over 40 amperes on the circuit.

The mystery is that in the summer, with only the fan running, I have had a few occasions where the 60 ampere breaker in the attic is tripping. The out-door unit is a separate 30 ampere 240V circuit so it is not involved.

Any thoughts on why this breaker is tripping under a 5-ampere load? I checked connections, no loose connections, no evidence of shorts, the motor turns freely and no smell of burned varnish or anything else. The only factor I can think of is that it happens when it is about 100+ degrees F in the attic.
Everything looks clean around the motor and fan. Replace filters often.

Could the high temperature cause the breaker to trip at such a low current? I believe the system was installed about 20 years ago.

Any help is appreciated. I am considering a new breaker for the attic unit but didn't want to spend 100 dollars unless I have to.

As a contractor I would never get involved with stuff like that past the breaker, ie appliances, hot tubs (especially hot tubs), but maybe it's yours or a friends. Maybe you could bypass the attic breaker and see if the garage breaker trips. Might tell you something.

 

[GerryB]

As a contractor I would never get involved with stuff like that past the breaker, ie appliances, hot tubs (especially hot tubs), but maybe it's yours or a friends. Maybe you could bypass the attic breaker and see if the garage breaker trips. Might tell you something.

You actually don't need a breaker in the attic. Put in a $15 pull out disconnect.