Circuit breaker question on AC unit.

Status
Not open for further replies.
H

hustler

New member
Location
san diego, ca
Just curious, the ac unit shows a minimum circuit of 31 amps required. The home has a 30 amp circuit breaker to the unit, and the breaker trips often when the unit is running.

I assume the issue is the size of the circuit breaker - that it should probably be a 40 amp breaker, correct?

Any advice would be appreciated.

Thanks!
 
Yes it should have a breaker that is higher than 31 amps. The unit usually states the mca- minimum circuit ampacity and the max circuit breaker-- However, do not change the breaker unless you know the wire size is the correct size.
 
Check the nameplate for the maximum circuit breaker size allowed. If the wire installed is rated for that much, then change the breaker.
 
480sparky said:
Check the nameplate for the maximum circuit breaker size allowed. If the wire installed is rated for that much, then change the breaker.
Click to expand...

Wouldn't you check the nameplate for the MCA and see if the wire were large enough for that not the MaxOCPD?
 
infinity said:
Wouldn't you check the nameplate for the MCA and see if the wire were large enough for that not the MaxOCPD?
Click to expand...

480sparky said:
Read the second sentence of my post.
Click to expand...

I did, you said "Check the nameplate for the maximum circuit breaker size allowed. If the wire installed is rated for that much, then change the breaker." The conductor only needs to be as large as the MCA not the size of the OCPD.

If the MCA is 20amps, the MaxOCPD is 30 amps and the conductor is #12 you can still change the breaker.
 
infinity said:
I did, you said "Check the nameplate for the maximum circuit breaker size allowed. If the wire installed is rated for that much, then change the breaker." The conductor only needs to be as large as the MCA not the size of the OCPD.

If the MCA is 20amps, the MaxOCPD is 30 amps and the conductor is #12 you can still change the breaker.
Click to expand...

Suppose the max breaker is 50, but the minimum circuit ampacity is 15?
 
The OP mentioned that the breaker trips while the unit is running (not necessarily at start-up) and that a 30A breaker is being used. This is purely an assumption on my part but if the breaker is 30A wouldn’t you presume that the wire size originally installed is #10?
  • Can you now install a 40A breaker ?
  • Is there a 35A trade size breaker on the market ?
  • Can we correct this by using a fused disconnect at the condenser?

Just curious:roll:
 
electrofelon said:
I suspect something else is going on. The mca should have an extra 25%, and usually I find running current to be about 2/3 of mca. I don't think that breaker should be tripping.
Click to expand...

I agree, if the unit starts with the 30 amp CB it should run on the 30 amp CB.
 
infinity said:
I agree, if the unit starts with the 30 amp CB it should run on the 30 amp CB.
Click to expand...


I agree to some extent. A breaker may be able to handle the startup load but if the amperage of the unit is over the overcurrent protective device then it will take a bit of time for the breaker to trip. Of course, it could be a weak breaker but if the breaker is undersized then it needs changing anyway
 
Dennis Alwon said:
I agree to some extent. A breaker may be able to handle the startup load but if the amperage of the unit is over the overcurrent protective device then it will take a bit of time for the breaker to trip. Of course, it could be a weak breaker but if the breaker is undersized then it needs changing anyway
Click to expand...

Yes but as electrofelon stated the MCA already has a 25% factor added to it so the actual running current should be much lower than the 30 OCPD protecting it. If for arguments sake the running current is 25 amps it should never trip under normal circumstances.
 
HVACR Loads

HVACR Loads

Single Phase HVACR loads always benefit from running MAX breaker size on the nameplate.
They also always benefit on start if single phase start components are added which may not always come factory installed.
Modern Thermostats generally incorporate an OFF-cycle time delay of 5 min.
Also essential if you do not have START GEAR.
Correctly installed single phase start components will lower the peak inrush current on start, often time by quite a noticable degree when read with a meter that will catch and record peak. If the breaker is tripping into the cycle and not on start I would look for an open RUN CAP, and check all connections on the compressor load all the way to the pot terminals.
 
infinity said:
Yes but as electrofelon stated the MCA already has a 25% factor added to it so the actual running current should be much lower than the 30 OCPD protecting it. If for arguments sake the running current is 25 amps it should never trip under normal circumstances.
Click to expand...
Correct, I was thinking the unit was running at 31 amps. My bad
 
Status
Not open for further replies.
Top