AC circuit breaker keeps tripping

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  #1  
Old 05-21-07, 04:50 AM
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AC circuit breaker keeps tripping

Hello,

My 30A AC circuit breaker keeps tripping. When I get it to reset the air conditioning works fine. With the breaker tripped the inside unit (fan) runs but the outside unit (compressor) does not.

Does this sound like the start capacitor is not helping to compressor start?

I looked at the capacitors and the connections are slightly corroded. If you think this could be the problem I can check them. Please let me know.

Thanks!
Ernie
 
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  #2  
Old 05-21-07, 08:55 AM
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That could be the problem. Does the breaker trip as soon as the compressor kicks on or after a few seconds of running?
 
  #3  
Old 05-21-07, 08:59 AM
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It trips as soon as the AC starts.
 
  #4  
Old 05-22-07, 03:38 AM
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Update: I checked the fan motor last night and it is free. I discharged and removed the caps but I could not easily test them since I only have a DMM (Fluke 87). I ran checks on them using the cap testing feature but I'm unsure if they are good or not. Is there are sure fire way to test the caps using a battery and a test light? How about with the Fluke?

Any help would be greatly appreciated.
 
  #5  
Old 05-29-07, 10:15 AM
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Update! I bought an anolog meter and tested the caps and they both tested good. I ordered and replaced them anyway since they looked original and they were cheap. The compressor failed to start and tripped the breaker on the 4th try. I went back down to the supply house and bought a hard start kit ($26) and installed it in parallel with the run cap. The unit worked Ok for a couple of days but tripped the breaker last night. I reset the breaker and it has been running fine ever since.

Are some of the hard start kits better than others? I need this system to last 1 more year.

Thanks in advance for your help.
Ernie
 
  #6  
Old 05-29-07, 12:14 PM
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Did you try replacing the breaker with a new one? Breakers do have mechanical components that can wear out and cause sensitive tripping. Also, is the A/C compressor a significant distance from the breaker panel?
 
  #7  
Old 05-29-07, 01:58 PM
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No I have not tried a new circuit breaker but the whole panel is only 4 months old. I can certainly try one though. I need an amp clamp and I'm thinking seriously about buying one.
 
  #8  
Old 05-29-07, 02:46 PM
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> 4 months old

Has the A/C ever worked with the breaker before, or is this the first use of the A/C with this new panel and breaker?
 
  #9  
Old 05-29-07, 03:05 PM
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On the rating plate of the unit what is the "Max Fuse or Breaker Size", and what is the "Min Circuit Ampacity"?
 
  #10  
Old 05-29-07, 03:36 PM
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Yep it worked fine with the old panel. The minimum breaker size per the data plate on the unit is 31A. My breaker is 30A and this is the one that is tripping.

I wish I knew what size breaker was in the old panel but I have no way to find out.
 
  #11  
Old 05-29-07, 04:12 PM
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31 amps ??

there should be a marking even old breaker will have a marking on the handle itself.

did you look at the A/C unit i know you did reply what the min size but did they listed the max size as well ?? it should say what is the max size

but ya have to becarefull with wire size the code is pretty tricky with the A/C system

if you are running with #10 wire you will be ok with 30 amp breaker but with A/C you can bump up to 40 amp breaker IF THE MAX SIZE ALLOWED [ sorry for upper case but i am serious with this one ]

i am sure few other will agree with me with this set up

Merci , Marc
 
  #12  
Old 05-30-07, 06:53 AM
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I looked at the unit data plate again and it says "fuse size" minimum is 31A and maximum is 50A. I will check the wire size in a bit. What size wire must I have to install a 40A breaker?
 
  #13  
Old 05-30-07, 07:17 AM
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Calculations for AC units do not follow the general rules for breaker size. It sounds like the electrician saw number 10 wire and installed a 30 amp breaker where he should have installed a 40 amp breaker.

The nameplate on the AC unit should also list min wire size as well as max fuse size. Also check to be sure that your breaker is HACR rated.
 
  #14  
Old 05-30-07, 07:43 AM
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I checked the (30A) breaker and it is HACR rated. The wire size is #10 AWG at the breaker. I looked at the shutoff box outside at the unit and it is a 40A breaker installed in a rainproof enclosure. I found 2 connection screws in the box that were loose and I tightened them.

Anything else?

This sight is awesome! Thanks for the help.

Ernie
 
  #15  
Old 05-30-07, 07:56 AM
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"Anything else" is what I was going to ask you. What more information do you need?
 
  #16  
Old 05-30-07, 08:05 AM
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If the nameplate on the unit says you can use number 10 wire, then replace the 30 amp breaker with a 40 amp breaker and all should be fine.

This is allowed because the breaker in this situation is not providing overload protection it is only providing short circuit protection. The overload protection is interal to the HVAC unit. (more specificly internal to the fan motor and compressor.)
 
  #17  
Old 05-30-07, 11:08 AM
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OK I checked the AC unit data plate and it does not show the wire size. I looked at the (partial) schematic on the inside of the door and it does not show the wire size either.

I have been unable to find the capacity of this unit because it is old. It is a Trane model OAUA-302-B. I did find the compressor listed in an interchange and it is a 3HP unit.

Can 10AWG wire support 40A current? All of the wiring looks healthy but I want to make sure.
 
  #18  
Old 05-30-07, 12:57 PM
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#10 on a 40 amp breaker is fine for feeding an A/C unit, as long as the rating plate says so.

You can size the conductors to the "Minimum circuit ampacity" rating.
You can size the breaker/fuse to the "Max fuse/breaker rating".

IMO your unit with a 31A min ckt ampacity would call for #8cu and up to a 50 amp breaker, according to the rating label.
 
  #19  
Old 06-01-07, 03:53 AM
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The data plate on the AC unit does not list wire size so I have no idea what they require. I did inspect the wire and it runs thru the rafters (drilled holes) in my basement. The wire is 10/2 with ground type NM.

Would you recommend I replace this wire with 8/2 with ground type NM to play it safe with the 40A breaker?

Thanks!
 
  #20  
Old 06-01-07, 08:34 AM
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The undersized wire could be contributing to or causing the breaker trip problem. The longer the cable, the greater effect it will have on the starting current. If it's just a few feet, then I doubt it's the problem; but if you're running 150' across the house then the #10 could be contributing. If the problem has not been resolved by the capacitor kit, then I think replacing the cable with 8/2 would be something else to try.
 
  #21  
Old 06-01-07, 09:02 AM
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I walked off the routing and the wire is approximately 60' from the panel to the box outside at the AC unit.

I was thinking it would be a good idea to install the larger wire if I install the 40A breaker.

Also is the type NM wire the correct kind to install? It has an off white plastic cover and is not in conduit excpet for the part that is outside.
 
  #22  
Old 06-01-07, 11:48 AM
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> I was thinking it would be a good idea to install the larger wire if
> I install the 40A breaker.

I don't think that what you have is unsafe, but it is not optimal. A #8 wire with a 40A breaker is certainly more correct. #8/2g NM-B is the correct cable if you choose to replace it.
 
  #23  
Old 06-01-07, 11:58 AM
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Don't know much about A/C units, but if the compressor is not unloading when off, there will be a high head pressure when it tries to restart, at that can kick out the breaker.
 
  #24  
Old 07-02-07, 08:52 AM
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Thumbs up

Update!

I installed the 40A circuit breaker about 3 weeks ago and the problem is FIXED! The installation was a snap and the AC has worked perfectly thru some terribly hot days.

Thanks to everyone for helping me t-shoot this problem.

Take care,
Ernie
 
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