Circuit Breaker Temperature

[dnbob]

I had measured the temperature of the circuit breakers in a 480/277 volt panelboard with an IR tester. A few 277 volt circuit breakers in the panel tested 15-20 degrees (F) above ambient. They were drawing between 9 and 10 amps on 20 amp breakers.

I looked at previous posts, and it seems this is in an acceptable range.

Wondering if this is an item of concern?

I tried to find information on UL 489, which I believe replaced NEMA AB-1, wasn't helpful.

Thanks!

 

[benaround]

Brian, it for you--

 

[don_resqcapt19]

I don't know what the permissible temperature rise is for the outside of the breaker, but it is 50?C for the rise at the internal contacts.

 

[brian john]

I have the data at work will post on Monday.

Did you do an FOP?

 

[Pierre C Belarge]

Remember:
As more current passes through a CBer, there will be a temperature rise. Take a gander at Table 310.16, the top of the table where the temperatures are written. You will see the temperatures have a potential of quite the rise with a load presented to the CBer.

 

[iMuse97]

I will be very interested in the outcome of this discussion. As a side note, I once went on a service call where the 100A main CB was too hot to touch with the back of my knuckles, and it was holding. They wondered if I could put in a bigger one for them. Needless to say, that was quite a bit of work before it was all good. They had called me b/c some of the branch CBs were tripping "too often" their words, not mine.

 

[Pierre C Belarge]

If one is to put a 30A load on a Type THHN, 12AWG copper conductor that is approximately 100ft long, what would you guess would be close to the temperature the conductor will rise to?

 

[iMuse97]

If one is to put a 30A load on a Type THHN, 12AWG copper conductor that is approximately 100ft long, what would you guess would be close to the temperature the conductor will rise to?

And this is a guess (with ambient temp. of 30 degrees C.): 40 degrees C.

 

[PetrosA]

I'm unclear on something - if a breaker is rated for a given temp, say 75?C, what does the ambient have to do with that? I would think that even in an ambient of 50?C, the 75?C limit still holds, or am I mistaken?

 

[Pierre C Belarge]

The temperature rating of the conductors provided in the table are similar to the temperature the conductors will reach when the current is at what the conductors are rated for.


The ambient temperature is the temperature about the CBer, not necessarily the room they are installed in. The ambient in the enlcosure may be higher than the room, depending on the loads of the circuits/feeders.


Higher ambients will affect the opening mechanism of the CBer.

 

[don_resqcapt19]

I was off a bit, per this Square D document the 50?C rise over ambient is at the breaker terminals.
That brings of the question of why we can use wire with a rating of less than 90?C? The ambient rating for most breakers is 40?C and with a permitted rise of 50?C at the terminations, the wire at that point could be running at 90?C and still meet the UL standards.

 

[brian john]

Never made it to the office, Busway blow up today , just got home 10:10 PM.

 

[480sparky]

Never made it to the office, Busway blow up today , just got home 10:10 PM.

And you didn't bring us any photos?

 

[dnbob]

Was just going to ask you if you had your info Brian!

Hope tomorrow is better.

Bob

 

[iMuse97]

Never made it to the office, Busway blow up today , just got home 10:10 PM.

Cool!!! or not. Hope it was somebody else's guy "what did that." or somebody else's mouse, or whatever. Everyone OK?

 

[ELA]

I was off a bit, per this Square D document the 50?C rise over ambient is at the breaker terminals.
That brings of the question of why we can use wire with a rating of less than 90?C? The ambient rating for most breakers is 40?C and with a permitted rise of 50?C at the terminations, the wire at that point could be running at 90?C and still meet the UL standards.

That was an interesting read Don,

I read it as the heated wire could be the cause of the breaker terminals temperature rise. The higher the wire temperature rating the more likely it will get the breaker too hot and as they say possibly nuisance trip. Therefore a lower temperature rating wire is desireable.

 

[dnbob]

Brian John,

If you have a minute to post your information, I would be interested!

Thanks,

Bob

 

[zog]

I had measured the temperature of the circuit breakers in a 480/277 volt panelboard with an IR tester. A few 277 volt circuit breakers in the panel tested 15-20 degrees (F) above ambient. They were drawing between 9 and 10 amps on 20 amp breakers.

I looked at previous posts, and it seems this is in an acceptable range.

Wondering if this is an item of concern?

I tried to find information on UL 489, which I believe replaced NEMA AB-1, wasn't helpful.

Thanks!

Here is the ANSI/NETA spec

Delta T between component and ambient air temperatures. Recommended Action
1?C - 10?C Possible deficiency; warrants investigation
11?C - 20?C Indicates probable deficiency; repair as time permits
21?C - 40?C Monitor until corrective measures can be accomplished
>40?C Major discrepancy; repair immediately

 

[don_resqcapt19]

Here is the ANSI/NETA spec

Delta T between component and ambient air temperatures. Recommended Action
1?C - 10?C Possible deficiency; warrants investigation
11?C - 20?C Indicates probable deficiency; repair as time permits
21?C - 40?C Monitor until corrective measures can be accomplished
>40?C Major discrepancy; repair immediately

Scott,
What am I missing when I read the NETA spec you quoted and the information in the SquareD document that I linked to in an earlier post says?

The temperature rise at the circuit breaker terminals must not exceed 50 ?C above ambient per UL Standard 489.

It seems to me that UL is saying a rise of up to 50 ?C at the termination points is permitted by the standard.

 

[radiopet]

Scott,
What am I missing when I read the NETA spec you quoted and the information in the SquareD document that I linked to in an earlier post says?

It seems to me that UL is saying a rise of up to 50 ?C at the termination points is permitted by the standard.

This is how I read that article.

Underwriter Laboratories Inc. (UL) standards require that molded-case
circuit breakers rated at 125 amperes or less be marked with the conductor
insulation-temperature rating. Table 1 contains a listing of wire temperature
ratings for Square D circuit breakers. The wire temperature rating is
determined by testing the circuit breaker under full-load current with
conductors sized for the appropriate temperature rating?60?C or 75?C. The
temperature rise at the circuit breaker terminals must not exceed 50?C above
ambient per UL Standard 489.