Message Board Thread - "Electrical breaker temp ratings"

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Electrical breaker temp ratings cdeery2 4/11/2008
I'm trying to obtain any information on electrical breakers as far as the heat threshold of the breakers. With an 80% max threshol load applied on any given breaker 120/208v what would should a typical temperature range be in. After the typical temperature range is exceeded I would assume that the breaker could possible have an internal fault, arcing bad connections.
Any thoughts or theroy's.
Thanks
 
Re:Electrical breaker temp ratings cdeery2 4/11/2008
cdeery2 wrote:
ing to obtain any information on electrical breakers as far as the heat threshold of the breakers. With an 80% max threshol load applied on any given breaker 120/208v what would should a typical temperature range be in. After the typical temperature range is exceeded I would assume that the breaker could possible have an internal fault, arcing bad connections.
Any thoughts or theroy's.
Thanks
I wanted to state that I'm looking at a 100A 3 phase 120/208v breaker at an average of 68-70 A per phase and reading a temperature of 110 F on this breaker.
 
Re:Electrical breaker temp ratings HITECHSOLUTIONS 4/12/2008
First of all you should be reading in the celsius degrees. All electrical components are based on celsius. NEMA has a standard that they use, and you can too. Or you can use what the facility wants to use. Also you need to know the ambient temp, the reflected temp. Can you give us a pic?
 
Re:Electrical breaker temp ratings IRJay 4/14/2008
UL489 states a breaker terminal area should not have a rise from ambient above 50 degrees C. You could apply this to the entire breaker as the material is all the same. This is a different rating than the terminal rating of 60 or 90 C which is a rating to determine wiring derating. Note here that this can result in allowable breaker temps above 190 degrees F.
I generally am concerned on breakers if the temp is above touchable temp of 130 F or 55 C. This is my rule of thumb. I would never want my breakers to be above the wire insulation temp rating.
 
Re:Electrical breaker temp ratings Douglas 5/9/2008
HITECHSOLUTIONS wrote:
f all you should be reading in the celsius degrees. All electrical components are based on celsius. NEMA has a standard that they use, and you can too. Or you can use what the facility wants to use. Also you need to know the ambient temp, the reflected temp. Can you give us a pic?
Just a quick comment "all" Square "D" type circuit breakers are "rated" on the side of "each" device 40 c, i would suggest that " tempature above that is a concern because that rating noted on the plastic body of the breaker...so if there is a tempature rise of more than say 10 per cent of that rating of 40C it may appear to do a follow up on the issue. Peace Douglas
 
Re:Electrical breaker temp ratings Ea1Services 5/9/2008
Interesting thread as the question posed has been troubling me as well. It seems that one step here would also be to reduce the reflective capability by the use of non reflective electrical tape. Would this give a more accurate reading?
 
Re:Electrical breaker temp ratings jvoitl 5/9/2008
1. The 40C rating on the side of a circuit breaker has nothing to do with the temperature of the breaker itself. It is the ambient temperature rating for the air around the breaker at which the current rating of the breaker is based. A higher air temperature can affect the trip characteristics of the breaker.

2. These breakers are thermal/magnetic. That is they have a magnetic funtion that will trip them with a short circuit, and a thermal function that trips them on an overload. By design they generate heat and that is not a defect.

As with any indirect temperature measurement the surface temperature of the breaker does not indicate the correct internal temperature. The only way to check if it is too hot is to compare it with another identical breaker under the same load and ambient conditions. When checking breakers the important thing is to check the line and load side connections. If they are under a pretty good load the breakers themselves will always be warm, sometimes way above 40C.
 
Re:Electrical breaker temp ratings brsw 11/7/2008
jvoitl wrote:
40C rating on the side of a circuit breaker has nothing to do with the temperature of the breaker itself. It is the ambient temperature rating for the air around the breaker at which the current rating of the breaker is based. A higher air temperature can affect the trip characteristics of the breaker.

2. These breakers are thermal/magnetic. That is they have a magnetic funtion that will trip them with a short circuit, and a thermal function that trips them on an overload. By design they generate heat and that is not a defect.

As with any indirect temperature measurement the surface temperature of the breaker does not indicate the correct internal temperature. The only way to check if it is too hot is to compare it with another identical breaker under the same load and ambient conditions. When checking breakers the important thing is to check the line and load side connections. If they are under a pretty good load the breakers themselves will always be warm, sometimes way above 40C.
can you tell me what is the basic principle between the failure rate of the breaker comparison to that of the wire
 
calculating temperature value brsw 11/7/2008
brsw wrote:
can you tell me what is the basic principle between the failure rate of the breaker comparison to that of the wire
can some tell me how to achieve the correct temperature using spot size reading
 
Re:Electrical breaker temp ratings brsw 11/7/2008
brsw wrote:
can some one tell me how to achieve the correct temperature using spot size reading
 
Re:Electrical breaker temp ratings JayP 4/27/2010
We have a 120 / 208, 3 ph panel,200 amp load center and we recently took a thermal image of the panel and discovered a 22 amp load on a 20 amp breaker. So, we upgraded to # 10 TTHN stranded and a 30 amp breaker. We still have the same temperature ratings on those specific breakers. Below is a before an after image. You can see on the second image, we moved one of the circuits to the top of the panel to dissipate some of the heat, rather than have them all together. Since the breakers have a thermal overload, at what temperature should the thermal overload trip. If I'm running a breaker at 60% of its capacity, I should be able to find an acceptable temperature range.
 
Re:Electrical breaker temp ratings JayP 4/27/2010
This is the after repairs image.
 
Re:Electrical breaker temp ratings JayP 4/27/2010
JayP wrote:
the after repairs image.
Sorry - the first picture is after the repairs, the second image posted is the pre-repair image.
 


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