a/c breaker sizing

Status
Not open for further replies.

Mgraw

Senior Member
Location
Opelousas, Louisiana
Occupation
Electrician
But as far as the compressor it should not trip out the overload it should be shutting down due to low or high pressure not due to current.

I agree, but most low end residential units don't have pressure controls. The biggest problem with compressors "flooding back" liquid refrigerant is the oil in the compressor mixes with the liquid refrigerant and takes the oil out of the compressor which will cause a compressor to heat up very quickly. Sometimes they seize up. The overloads don't kick out to around 300 degrees.
 
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
The cutouts don't always work and in this instance we are already dealing with a unit that had an undersized CB. The question we need to be addressing is "What changed?" Most likely changing the CB will keep them from having to reset it but did we solve or just cover the problem.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
The cutouts don't always work and in this instance we are already dealing with a unit that had an undersized CB. The question we need to be addressing is "What changed?" Most likely changing the CB will keep them from having to reset it but did we solve or just cover the problem.
As the equipment ages, sometimes the current will go up. I don't see any reason for any additional trouble shooting when the equipment is tripping a breaker smaller than the required minimum size breaker. It would be operating within the design specs as long as it is not tripping a 50 amp OCPD.
 

iwire

Moderator
Staff member
Location
Massachusetts
As the equipment ages, sometimes the current will go up. I don't see any reason for any additional trouble shooting when the equipment is tripping a breaker smaller than the required minimum size breaker. It would be operating within the design specs as long as it is not tripping a 50 amp OCPD.

That was my thinking entirely. As I posted above I would put my amp clamp on while I was there to see it was not drawing more than it was labeled to but beyond that I would install a proper breaker and move on.
 

ceb58

Senior Member
Location
Raeford, NC
i put the clamp on ammeter on the circuit conductors: compressor 18amps
fan motor 1.8 amps..i let the unit run for over an hour, it never wnt over 20amps total..

i purchased a 40 amp breaker, and compressor hard-start kit.
installed both and called it a day.

thanks for the All the replys!:)

There is a 30 amp breaker supplying a unit with a label requiring at least a 35 amp breaker.

I say go for the obvious first. :)

The undersized breaker is just probably tired. Even though it should handle what you read as amp draw you are not taking into account for the inrush on start up. Over time the breaker has just given up.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
It has been a while so bear with me. Dirty air filters may cause a unit to trip on overload. Less air flow across the evaporator will cause the freon to boil later than what is intended. Eventually the evaporation will still be taking place in the return lines to the compressor making it work harder. Compressors are designed to pump gas, not liquid. Checking the air filters was always one of the first things we did on service calls. A dirty evaporator will cause the same problem.

As Bob mentioned I was speaking about the blower unit which I thought of when I read air filters.
 

kwired

Electron manager
Location
NE Nebraska
There is a 30 amp breaker supplying a unit with a label requiring at least a 35 amp breaker.

I say go for the obvious first. :)

Actually a dirty filter would make the unit work less not more which would cause it current draw to decrease not increase.

The blower will work less, the compressor will have longer run cycles. Refrigerant pressure will be higher and will likely result in higher compressor current. Also you eventually may experience liguid refrigerant that never evaporated, enter the compressor. Liquid does not compress and is a bad thing. Scroll compressors handle it better than rotary compressors.

i put the clamp on ammeter on the circuit conductors: compressor 18amps
fan motor 1.8 amps..i let the unit run for over an hour, it never wnt over 20amps total..

i purchased a 40 amp breaker, and compressor hard-start kit.
installed both and called it a day.

thanks for the All the replys!:)

hard start kit will do nothing for running current. I also suggest using a megohmeter on the branch circuit as well as the compressor I recently had one that was tripping breaker (although not undersized) similar to your situation. Running current was normal but would trip after running for a few hours. Found conductor insulation problems with arc tracings in the flex from the disconnect to the condensing unit. Replaced conductors and was not called back after that.

It has been a while so bear with me. Dirty air filters may cause a unit to trip on overload. Less air flow across the evaporator will cause the freon to boil later than what is intended. Eventually the evaporation will still be taking place in the return lines to the compressor making it work harder. Compressors are designed to pump gas, not liquid. Checking the air filters was always one of the first things we did on service calls. A dirty evaporator will cause the same problem.

I agree.

I see what you where saying, I am sure Infinity was talking about the fan itself not the compressor.

But as far as the compressor it should not trip out the overload it should be shutting down due to low or high pressure not due to current.

OP is not tripping an overload he is tripping the (undersized) branch circuit breaker.
 

la2151

Member
Location
california
air cond conducter sizes

air cond conducter sizes

Does this apply to resi A/C units only or is code for commercial rooof top units as well?
 

la2151

Member
Location
california
air cond conducter sizes

air cond conducter sizes

I am also asking if this is code to use larger breaker for wire size on commercial roof top air condioners.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Does this apply to resi A/C units only or is code for commercial rooof top units as well?

I am also asking if this is code to use larger breaker for wire size on commercial roof top air condioners.
It applies to all HVAC, as well as other motor loads.
 
Status
Not open for further replies.
Top