a/c breaker trip

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jetlag

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Eatonton, Georgia
My son works for a motel chain. He said the outside condenser is supplied by #10 conductors and a 35a breaker. He said the name plate shows 37 a max draw. I guess thats the same as full load amps. He says the breaker trips often. I told him I would check amps while running and if over 30 , I would run #8 conductors first.. If load is in the 20's a 50a breaker or even 2.5 times the load is ok for start load on a regular breaker. He doesnt know if the 35a is a time delay breaker or not . I also told him if the running load is much over the 37a max there is problem with the compressor,, Does this sound like good advise, Hey If I scew up its me but if I cause someone else to do it that bothers me more.
 
Tell him to hire an electrician to look at this. First, breaker to bus connections and conductor to breaker connections. Then amprobe while equipment is running, could be an equipment problem.
 
Depends by what he means by "max draw". He needs to look at the nameplate and see if it lists Minimum Circuit Ampacity (MCA) and Max Breaker values. If the max breaker is 35A, then the install seems reasonable. If the MCA is 35, then its no wonder it trips often.

The wires need to be sized per the MCA value. The breaker needs to >= MCA is not more than the max breaker.

If you have no MCA value, but have an RLA for the compressor and FLA for the fan, then you'd take RLA*1.25 + FLA and that will be close to the MCA. It is just nicer when the factory calculates the MCA because there could be other loads you don't know about.

The measured running current should be near the sum of the RLA and FLA, or about 80% of the MCA (depending on what numbers he has available).
 
Sounds bit high for normal motel room. How many tons ? He needs to know the running amps total. Is always a chance the unit it over charged. If he is in charge of doing the AC work have him check freon level and put amp probe on it. Anything over 30 after its running few minutes is too high for #10. He might be triping only on start up. Add a hard start cap and it might hold. Without actual numbers its guess work.
 
chris kennedy said:
Tell him to hire an electrician to look at this. First, breaker to bus connections and conductor to breaker connections. Then amprobe while equipment is running, could be an equipment problem.
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He is an inplant electrician ,originally trained under me and I have a state masters license for 18 years. And the post states that I advised him to check the running amps it could be equiptment problem, so your post is pointless.
 
suemarkp said:
Depends by what he means by "max draw". He needs to look at the nameplate and see if it lists Minimum Circuit Ampacity (MCA) and Max Breaker values. If the max breaker is 35A, then the install seems reasonable. If the MCA is 35, then its no wonder it trips often.

The wires need to be sized per the MCA value. The breaker needs to >= MCA is not more than the max breaker.

If you have no MCA value, but have an RLA for the compressor and FLA for the fan, then you'd take RLA*1.25 + FLA and that will be close to the MCA. It is just nicer when the factory calculates the MCA because there could be other loads you don't know about.

The measured running current should be near the sum of the RLA and FLA, or about 80% of the MCA (depending on what numbers he has available).
Click to expand...

Thanks for that, that is one great overview. I'll pasted it elsewhere...

For all of you out there that don't deal with motors a lot, well pay attention...
 
thanks jim

thanks jim

Jim W in Tampa said:
Sounds bit high for normal motel room. How many tons ? He needs to know the running amps total. Is always a chance the unit it over charged. If he is in charge of doing the AC work have him check freon level and put amp probe on it. Anything over 30 after its running few minutes is too high for #10. He might be triping only on start up. Add a hard start cap and it might hold. Without actual numbers its guess work.
Click to expand...

ITs not for a motel room , its for another area I think its 4 tons or more . It was late today so he plans more tests tomorrow. I,,ll remind him to make sure unit is not over charged
 
If the amps are high have him check the contactor points for the compressor. They can be pitted and will cause a unit to over amp. Also check the wires at the compressor, sometimes they get loose.
 
thanks suemarkp

thanks suemarkp

suemarkp said:
Depends by what he means by "max draw". He needs to look at the nameplate and see if it lists Minimum Circuit Ampacity (MCA) and Max Breaker values. If the max breaker is 35A, then the install seems reasonable. If the MCA is 35, then its no wonder it trips often.

The wires need to be sized per the MCA value. The breaker needs to >= MCA is not more than the max breaker.

If you have no MCA value, but have an RLA for the compressor and FLA for the fan, then you'd take RLA*1.25 + FLA and that will be close to the MCA. It is just nicer when the factory calculates the MCA because there could be other loads you don't know about.

The measured running current should be near the sum of the RLA and FLA, or about 80% of the MCA (depending on what numbers he has available).
Click to expand...

Its my fault he calls it max draw, it is the MCA as stated at 37a on the name plate so it seems to me the #10 conductors and 35a breaker was not a proper install. He will look for more spec tomorrow .I dont see how they could expect to start the compressor with a 35a breaker .
 
jetlag said:
Its my fault he calls it max draw, it is the MCA as stated at 37a on the name plate so it seems to me the #10 conductors and 35a breaker was not a proper install. He will look for more spec tomorrow .I dont see how they could expect to start the compressor with a 35a breaker .
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I would agree. If the 37 is actually the MCA, then the #10 would be undersized and 35 would be puhing it as the OCP. Did he mention what the nameplate MOCP is ?
 
MCA = minimum circuit ampacity. If it is only 35 amps then the #10 wire is okay at 75C. Use a 50 amp breaker. If it is 37 amps then you need #8
 
jetlag said:
Its my fault he calls it max draw, it is the MCA as stated at 37a on the name plate so it seems to me the #10 conductors and 35a breaker was not a proper install. He will look for more spec tomorrow .
Click to expand...
Look for MO(C)P while you're there.
 
In my experience it is rare to see a A/C unit run at MCA or more unless it has a problem. Dirty coils, pitted contactor, loose connection, over charged, low voltage, "tight" compressor can all cause a unit to over amp. I have known a few A/C contractors who would fuse a unit at or right above MCA to get more service calls. They would claim it was to protect the compressor. I got alot of good customers because of them.
 
Thanks Mgraw

Thanks Mgraw

Mgraw said:
In my experience it is rare to see a A/C unit run at MCA or more unless it has a problem. Dirty coils, pitted contactor, loose connection, over charged, low voltage, "tight" compressor can all cause a unit to over amp. I have known a few A/C contractors who would fuse a unit at or right above MCA to get more service calls. They would claim it was to protect the compressor. I got alot of good customers because of them.
Click to expand...

I think this is the problem and today he will find out if the unit runs below the mca , but the 35a breaker has prob starting the compressor and is also 2 a below the mca of 37a. Before my son was hired they had to call electrician for everything, so like you say , protect the compressor was more like pad the wallet.
 
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