Hot breaker

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Crw16

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Brick, NJ USA
I have a 3 phase sub panel w/ 200a main, breaker is only for convience of isolating panel for service. Within panel I have a 100a 3phase branch breaker supplying roof top AC unit. Branch breaker is running very hot to touch when AC is working hard on hot days. There has been occasion when 200a main trips.Not due to being overloaded. AC mechanic wants to relocate 100a breaker into seperate enclosure to attempt to alliviate heat issue. Is this a viable solution or is issue in roof top unit? Unit is aging and problem has been repetitive for last few years. Looking for direction.
 
I presume there is also other loads in the panel, so the main is seeing the AC plus some other load?

AC running continuously will heat up a breaker more than one may realize and is still "normal" But if it is tripping there is some problems.

Possible breaker to bus connection is poor (on either the 200 or the 100 amp breaker) and adding even more heat than normal. Situations like that you might want to replace both breakers as well as the bus, because heat has likely compromised all three of them and if you reuse any of them that problem may come back.
 
Welcome.

Probably due to terminations or breaker contact with panel bus, especially with plug-in breakers. I would check conductor terminations and check the condition of bus stabs for heat discoloration. Have an IR thermometer?

Added: ​Beat me!
 
LarryFine said:
Welcome.

Probably due to terminations or breaker contact with panel bus, especially with plug-in breakers. I would check conductor terminations and check the condition of bus stabs for heat discoloration. Have an IR thermometer?

Added: ​Beat me!
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I agree. Bad connections are thee most common cause of heat problems. Breaker could be bad internally ( bad contacts).

After checking the terminations they need to check to see what the current draw of this unit is when running. The breaker is going to be sized for starting current so when it's running normally it shouldn't be enough to heat the breaker up that much.
 
growler said:
I agree. Bad connections are thee most common cause of heat problems. Breaker could be bad internally ( bad contacts).

After checking the terminations they need to check to see what the current draw of this unit is when running. The breaker is going to be sized for starting current so when it's running normally it shouldn't be enough to heat the breaker up that much.
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Air conditioner breaker is still often the warmest breaker in a panel because it often is the only load that runs continuously or near continuously. So a air conditioner breaker that is warmer than the rest isn't too abnormal, but when it is getting hot enough that things are tripping there is usually a connection problem somewhere.
 
I'm with the others.

I would verify the AC load, if the load was acceptable and the connections are tight and you still have this issue, I'd be inclined to think the breaker internals may be in poor shape.

A fall of potential test or thermal imaging camera could narrow it down to give you a definitive answer, or you could just replace the breaker if you're so inclined.

If this breaker is up against other heavily loaded breakers, you may just need to move it down the panel a space or two, to help it shed the heat.
 
Cow said:
I'm with the others.

I would verify the AC load, if the load was acceptable and the connections are tight and you still have this issue, I'd be inclined to think the breaker internals may be in poor shape.

A fall of potential test or thermal imaging camera could narrow it down to give you a definitive answer, or you could just replace the breaker if you're so inclined.

If this breaker is up against other heavily loaded breakers, you may just need to move it down the panel a space or two, to help it shed the heat.
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But it is tripping the main and not the branch breaker. Problem may be more than just the branch breaker.

I'd almost bet that if one pulled some breakers and took a look at the bus, it will show signs of overheating.
 
kwired said:
But it is tripping the main and not the branch breaker. Problem may be more than just the branch breaker.

I'd almost bet that if one pulled some breakers and took a look at the bus, it will show signs of overheating.
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My mistake, skipped right over that. I agree it's worth taking a look at the bus, my recommendation for testing the branch breaker would also apply to the main as well then.
 
Not sure if there is an answer to this one, but once in awhile I'll open a panel door and shoot temps on the breakers with my IR, is there a "normal" temp range?
 
mtfallsmikey said:
Not sure if there is an answer to this one, but once in awhile I'll open a panel door and shoot temps on the breakers with my IR, is there a "normal" temp range?
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Yes, you should expect them to be ambient or warmer.

OH, you mean how much warmer? Too many with thermal cameras see a breaker warmer than others and report it as bad. PROBABLY not, just carrying more current than others. If a 3 phase motor breaker or device has higher temperature on one of the 3 current paths, additional study is probably justified.

But when the 3 kids just finished their showers and the electric water heater breaker is warmer ... almost certainly normal. Or there is a turkey cooking in the oven, and 3 upper elements working on other meals and the associated breaker is warmer, PROBABLY no issue.

Breakers usually include THERMAL trips ... I^2*R ... converts electrical energy to thermal energy ... by design ...

We must THINK!
 
40C for general outside plastic case. 65C for metal operating handle, 85C if plastic handle. These are maximum normal levels.

I tell folks what matters is when you notice a change. When something goes from never being above room temperature to being hot you need to take action.
 
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