How hot is too hot?

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tonype

Senior Member
Location
New Jersey
When reviewing a breaker panel, I use an infrared thermometer to take a quick check of temps. Today in a diner, a 2-pole 20-amp breaker (Cutler Hammer) for some item in the kithcen was about 150 degrees F. Never came across this high. Is there any guideline on what may constitute a problem?
 

WorkSafe

Senior Member
Location
Moore, OK
I'm not a electrician...


Stick a amp meter on there and see how much the circuit is drawing. That would be a starting point to see if there is even a problem.
 

Sierrasparky

Senior Member
Location
USA
Occupation
Electrician ,contractor
I would think your temp is too Hot that close to 70deg. Is the breaker hot to the touch? You need to check the connections, the amperage , the buss.

If all is good then the breaker is failing in my opinion.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
What is the normal operating temperature of a standard breaker when all connections are good and it's operating near it's maximum ampacity? Without knowing that I don't see how anyone can answer the question.
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
Assuming it was applied and installed correctly, common molded case circuit breakers (MCCB) at rated current effectively permit a maximum operating temperature of 90?C (194?F) in a 40?C (104?F) ambient.
 

tonype

Senior Member
Location
New Jersey
I would think your temp is too Hot that close to 70deg. Is the breaker hot to the touch? You need to check the connections, the amperage , the buss.

If all is good then the breaker is failing in my opinion.

Breaker was hot to the touch.

As an Engineer/inspector, I do not stick stuff in panels - leave it to you guys who are trained for this. Playing on the safe side, I will advise client to have an electrical contractor review this.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
Assuming it was applied and installed correctly, common molded case circuit breakers (MCCB) at rated current effectively permit a maximum operating temperature of 90?C (194?F) in a 40?C (104?F) ambient.
I have never seen a 90?C rating for any part of a molded case breaker. As I recall the operating handle is only allowed to be at 60?C.
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
I have never seen a 90?C rating for any part of a molded case breaker. As I recall the operating handle is only allowed to be at 60?C.
You're right and thanks for the correction Jim. I shouldn't answer questions from old memories. 60?C (140?F) would still be very warm to the touch and could easily cause a second degree burn under the right conditions. Nevertheless, a 150?F reading is excessive under any conditions.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
You're right and thanks for the correction Jim. I shouldn't answer questions from old memories. 60?C (140?F) would still be very warm to the touch and could easily cause a second degree burn under the right conditions. Nevertheless, a 150?F reading is excessive under any conditions.
For the trivia people.
Based on the NEMA standard AB-1-1986 (yeah I know its old).

Maximum Temperature rise limits above rated ambient at 100% load:
Contact parts, copper - 45?C
Metal parts - Limited solely so that damage is not caused to itself or insulating materials
Main operating means, parts of insulating material - 60?C (based on 25?C ambient)
Main circuit terminals for external connections - 50?C

If temperature rises on wiring terminals exceed 50?C, the manufacturer shall specify conductors with 90?C insulation sized using the 75?C ampacity.
 
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