Compressors Tripping Breakers

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When a compressor motor Has an intermittant short is there any way to identify it?
I have had several request from A/C & Refrigeration mechanics over the years to replace the circuit breakers feeding their equipment because they claimed it was bad because it had tripped out and they found nothing wrong at the time (they checked the amperage) with the unit. So far every time it has been the compressor and not the breaker.

Jeff
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
Normally a megger will identify a "bad" motor, but not necessarily a "intermittent short". Most of the failures I have seen with compressor motors are insulation failures and are readily identified by a megger test.
Has one been performed on the failures you are familiar with ?
 

technoid52

Member
Location
PA
When a compressor motor Has an intermittant short is there any way to identify it?
I have had several request from A/C & Refrigeration mechanics over the years to replace the circuit breakers feeding their equipment because they claimed it was bad because it had tripped out and they found nothing wrong at the time (they checked the amperage) with the unit. So far every time it has been the compressor and not the breaker.

Jeff
Has your utility company been giving out a few power winks when your not there? That would make the motor current rise high enough to blow the breakers. Freon Pressures have to equalize befor a restart.
 

GG

Senior Member
Location
Ft.Worth, T.X.
I do A/C work as well as electrical. Every time I have found a tripped compressor breaker I have installed a hard start kit (start capacitor) at the condenser and the breaker did not trip again. I would say of the 10 or so brekaers I found tripped, a hard start kit fixed the problem. I wonder if the A/C techs had hard start kits installed at the time they requested you to change out the breaker?
 

charlietuna

Senior Member
Both you and the A/C contractor are only guessing without actually knowing what the voltage and current flow was at the time of the trip! If the breaker's rating is close to the full load rating of the compressor it will easily trip due to a low voltage condition caused by other equipment or your power company. I usually suggest installing one of my data loggers on the effected circuit for a week--then provide the owner and the A/C contractor with a copy of the readout and my suggested course of repair.
 

cowboyjwc

Moderator
Staff member
Location
Simi Valley, CA
We used to find that when that started happening, it was usually an older unit or maybe a not well maintained unit. Very rarely was it a bad breaker.
 
This particular compressor is pulling 28amp 1ph (when running properly) and is fed with #8 thhn on a 50amp c/b.
I found out after I posted yesterday that they have replaced 2 contactors on the condensing unit as well.
A recorder would come in handy as we are really doing a process of elimination by ruling out the circuit breaker and I'm sure they will try a hard start kit as the unit currently does not have one, after that if the problem still exist it seems like the next step is the compressor.
Power surges are a possibility and the recorder would point that out.
I have put in to purchase one but budget issues may not allow for it at this time.
Thanks for the input.
 

Jim W in Tampa

Senior Member
Location
Tampa Florida
If 2 contactors have burned up i would say either they were undersized or being over loaded.
A hard start cap is cheap and easy. While it might mask the real problem it is a quick fix.
Many other issues are involved such as head pressure from dirty coils,filters ect. If the AC man is qualified to check the charge (not as simple as just reading the 2 gauges) and he has the right amp readings then there might be problems with the start cap. Breaker is unlikely but can't be ruled out. Also things like tight connections. Lastly we must remember that compressors do wear out.
 

growler

Senior Member
Location
Atlanta,GA
When a compressor motor Has an intermittant short is there any way to identify it?
I have had several request from A/C & Refrigeration mechanics over the years to replace the circuit breakers feeding their equipment because they claimed it was bad because it had tripped out and they found nothing wrong at the time (they checked the amperage) with the unit. So far every time it has been the compressor and not the breaker.

Jeff

I have been on calls when the compressor had a dead short and the A/C service tech said it was the breaker , because the breaker keeps tripping.

I really don't care because I get paid to point out the real problem and I change out the breaker because those idiots let it trip 50 times.

There is an old saying that you should never look a gift horse in the mouth. A/C service techs are a boon to the electrical service industry.

It's their job to learn how to check out those compressors and mine to show up when they don't.
 

growler

Senior Member
Location
Atlanta,GA
This particular compressor is pulling 28amp 1ph (when running properly) and is fed with #8 thhn on a 50amp c/b.
I found out after I posted yesterday that they have replaced 2 contactors on the condensing unit as well.

Did they check out their service lines because I have been told that a kink or clog in the line will cause problems like this.

As I say I just install a new breaker and make sure all connections are tight and then it's their problem. You may want to meg your feeder cable just to be on the safe side.
 

Jim W in Tampa

Senior Member
Location
Tampa Florida
Did they check out their service lines because I have been told that a kink or clog in the line will cause problems like this.

As I say I just install a new breaker and make sure all connections are tight and then it's their problem. You may want to meg your feeder cable just to be on the safe side.

It is called a restriction and should show up on gauges. There also is a circuit board for time delay so it does not start till pressure had time to equal itself. Many AC men are weak in the electrical end of the job. Have had to tell more than one how to reverse the direction on 3 phase. Teach them one item at a time. $$$$$$$$$$$$$$$$$$$$$$$$$
 

Mgraw

Senior Member
Location
Opelousas, Louisiana
Occupation
Electrician
I would install a hard start kit as well as a time delay. If the compressor tries to start before the refrigerant has time to equalize the compressor can draw locked rotor amps for several seconds before the internal overload will kick it out. Could also be someone playing with the t-stat. Also check for insects between the contacts, I have seen ants inside the contactor cause the points to burn.
 
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