Operating temperature of 70 amp breaker

[Greg1707]

I have a customer concerned about the operating temperature of a 70 amp breaker feeding an electric furnace. The furnace is drawing 62 amps and the terminals on the breaker are heating up to 118 degrees F. I checked the bus and found no discoloration. Is this temperature within normal operating range?

 

[MAC702]

That's ambient around here. Never mind surface temps of a panel...

 

[masterinbama]

Generally you should load a breaker beyond 80%

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[jumper]

Generally you should load a breaker beyond 80%

Sent from my LGL157BL using Tapatalk

Missing a “not” in your sentence, I assume typo.

 

[K8MHZ]

I have a customer concerned about the operating temperature of a 70 amp breaker feeding an electric furnace. The furnace is drawing 62 amps and the terminals on the breaker are heating up to 118 degrees F. I checked the bus and found no discoloration. Is this temperature within normal operating range?

That's only 48 C. To me, that would be within specs. But if the temp in question was increasing over time, there may be a problem somewhere.

 

[masterinbama]

Yes, hard to type with a shattered screen.

Missing a “not” in your sentence, I assume typo.

Sent from my LGL157BL using Tapatalk

 

[jumper]

That temperature is warm, not hot or abnormal.

 

[mbrooke]

What is hot for use is ok for electrical equipment. Keep in mind that breakers will produce heat, they have to in order to provide protection.

 

[iceworm]

I have a customer concerned about the operating temperature of a 70 amp breaker feeding an electric furnace. The furnace is drawing 62 amps and the terminals on the breaker are heating up to 118 degrees F. I checked the bus and found no discoloration. Is this temperature within normal operating range?

For a molded case CB, built to UL 489:
Termination for standard rating (not 100% rated) temperature rise NTE 50C (that's 90F). So with a 25C ambient, that would be 75C (167F)

Termination temp max is 50C rise over 40C ambient ==> 90C (194F)

The device is running ~90% load. 118F is okay. However, I would recommend checking all 6 terminations and look for a variation in temperature. That can indicate a problem with terminations, or even contacts.

the worm

 

[Jraef]

50C = 122F, not 90F.

30C = 86F
40C = 104F

60C = 140F

UL test temperature rise is 50C for the breakers in free air, but all UL enclosed equipment is designed around 40C max. ambient.

Then trip calibration temperature on CBS is 30C. Above 30C ambient the breaker may end up tripping a little earlier, not failing.

As this all relates to the original question though is that the recorded temperature is not something I would be concerned about.

 

[Russs57]

I'd be more concerned about rather or not that breaker is rated for 100% use than actual temperature. To me, temperature is more relevant when you notice a change. If the breaker used to run cooler than I'd take action. Without that knowledge I'd be looking to see if it is rated to carry more than 80%.

 

[ptonsparky]

I would be inclined to do a FOP across each pole. My older not top of the line camera would also be able to indicate if one pole was worse than another.

Still 60+ amps on a 70. I don’t know if I’ve ever seen a 100% rated breaker.

 

[iceworm]

For a molded case CB, built to UL 489:
Termination for standard rating (not 100% rated) temperature rise NTE 50C (that's 90F).

50C = 122F, not 90F.

jraef -
That was "temperature rise". And yes, 90F Rise = 50C rise

 

[iceworm]

...Still 60+ amps on a 70. I don’t know if I’ve ever seen a 100% rated breaker.

I haven't - not at that size anyway. And, yes, 90% is more than I would be comfortable with

 

[retirede]

Operating temperature of 70 amp breaker

jraef -
That was "temperature rise". And yes, 90F Rise = 50C rise

Interesting