Replace 20 amp breaker with 25 amp breaker

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  #1  
Old 07-17-15, 07:11 PM
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Replace 20 amp breaker with 25 amp breaker

Hi all-

Long story short, I have a 20 amp dual pole breaker with 12 gauge wire for central air currently. The a/c unit needs 25 amp. Had a guy out to service the a/c and he was the one who told be that it needed to be 25. He was going to swap out the 20 with a 30 amp until he noticed it was 12 gauge wire. He said he didn't want to run the risk of starting a fire, but that I could go buy a 25 amp and replace it myself no problem. Is this true?
 
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  #2  
Old 07-17-15, 07:32 PM
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Wire Capacity Chart

According to a chart on that site, the answer is 23 amps, so I suppose it's close enough. Wait for other answers.
 
  #3  
Old 07-17-15, 08:10 PM
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Yes, you can upsize the CB only on dedicated motor circuits, like your a/c. 25A is fine on 12AWG. You may see the mark HACR on the breaker; this means it has a time delay characteristic to accommodate high inrush motor currents, esp. compressors.
 
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Old 07-17-15, 08:39 PM
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Hopefully it is a short run between your panel and the condenser. A long piece of #12 will have a lot of voltage sag/drop on compressor startup.
 
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Old 07-18-15, 06:26 AM
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Thanks for the info guys. The panel is about 10 feet away from the unit, so not too far of a run.
 
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Old 07-18-15, 07:46 AM
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If the unit is existing and the 20 amp breaker isn't tripping I'd just leave it alone. If this is a new unit, check the data plate for the Minimum Circuit Ampacity (MCA). If it is 20 amps or less, the #12 wire is fine. Then check the Maximum Overcurrent Protection (MOCP) or Max Fuse Size. If it says 25 amps or higher you can change the breaker to 25 amps.
 
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Old 07-18-15, 08:03 AM
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The unit is not new, it's from 2004. A/C tech said the unit needs a 25 amp. I think they just never changed, or upgraded breaker, when they replaced unit. It is tripping. Did it a couple times earlier this year, now more frequent. I guess the compressor is starting to go and when it is starting up it sometimes throws the breaker. He put a hard start kit on the a/c and it hasn't tripped yet, but with a 25 amp it would trip less often because of the spikes when turning on.
 
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Old 07-18-15, 09:43 AM
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Again, check the data plate on the unit.
 
  #9  
Old 07-18-15, 06:52 PM
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The unit is not new, it's from 2004. A/C tech said the unit needs a 25 amp.
What does the data plate say? If the info is not on the data plate, maybe someone can find the info with the manufacturers name and model number.
 
  #10  
Old 07-18-15, 07:19 PM
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It says min 25 amp, max 30 amp.
 
  #11  
Old 07-18-15, 07:22 PM
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I did notice that the 25's are harder to find (or obtain right away). I wonder if that is the reason why a 25 wasn't installed when they installed the a/c.
 
  #12  
Old 07-18-15, 07:29 PM
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25 amps was never considered a standard circuit breaker size and was always available on special order only till the last several years. Since A-C units have gotten so much more efficient and the required amperage has dropped, so has the circuit protection. Now, most supply houses stock the 25 amp breakers. I believe the box stores have also started stocking some of them as well. In your case, I believe I'd use the 30 amp breaker.
 
  #13  
Old 07-18-15, 07:33 PM
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Yeah, I ordered a 25 amp from Home Depot. So a 30 would be ok with 12 gauge wire?
 
  #14  
Old 07-18-15, 07:42 PM
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So a 30 would be ok with 12 gauge wire?
Sure. The rules are different for motor loads than they are for a typical branch circuit. You didn't tell us the MCA, but I am willing to bet it's 20 amps or less so the #12 wire is fine. If the MCA is between 20 and 30 amps, you need to rewire the circuit with #10 wire. I am also guessing that this is a little 2 or 2 1/2 ton unit.
 
  #15  
Old 07-18-15, 08:04 PM
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Ok cool. I thought the 25 amps was the MCA number. I looked at it again and it says "Minimum Supply Circuit Ampacity" 19 / 19 amp. That must be the number you are looking for.
 
  #16  
Old 07-18-15, 08:37 PM
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Since the 19 is less than 20 you can use the #12 with up to a 30 amp breaker.
 
  #17  
Old 07-19-15, 06:12 AM
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Thanks everyone! I appreciate the help!
 
  #18  
Old 07-19-15, 07:55 AM
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Since the 19 is less than 20 you can use the #12 with up to a 30 amp breaker.
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