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breaker temperature

Posted by cappo11 (My Page) on
Sat, Sep 1, 07 at 17:51

was wondering if anyone is familiar with the practice of taking a breaker's temperature with a infrared thermometer.
a home inspector told me that if the temp is above 104, then it must be replaced. i have never heard of this. thanks for any advice


Follow-Up Postings:

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RE: breaker temperature

"a home inspector told me that if the temp is above 104"

Just another case of a H-I not having a clue about what he is talking about.

Most breakers are rated @ 75c. This is 167f.
A breaker that is 110f and even hotter is simply a sign of a heavily loaded breaker. I would check the connections and the load long before I'd just throw a new breaker in.
Most often the breaker is NOT the problem, yet folks throw new parts at a problem until it goes away. The thought is that changing the breaker is the "easy" way out.


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RE: breaker temperature

Why don't you simply ask to see something in writing, something official and not published by the H-I nutcase journal, that states what the inspector told you. As Petey pointed out, this is well within the NORMAL operating temperature of the breaker.

By the way, what are your options when the outside temperature is, oh, say 105-110 degrees like it has been in the southwest lately? Daily panel changes? Idiots.....


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RE: breaker temperature

... this is well within the NORMAL operating temperature ...

Unless the home inspector's infrared thermometer is reading in celsius.


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RE: breaker temperature

"Unless the home inspector's infrared thermometer is reading in celsius."

104C wold then be way to high.
Other problems (like that breaker and the ones around it not staying closed) would be readily apparent.

Some HI got a new toy and is trying to look more 'scientific'.

Breakers dissipate power as part of the thermal portion of thermal-magnetic, though in the actual device the magnetic coil is often also the power dissipative element.


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RE: breaker temperature

thanks for your help. i spoke with the inspector and he says that underwriters laboratories (UL 489) states that normal operating temperature of a breaker should be 40c or 104f.
apparently this inspector feels that any temp above that indicates a bad breaker. won't be asking any more advice from this guy


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RE: breaker temperature

I have one of those things, IR non contact laser guided heat gun... anyhow my 200a/mb ite panel cover is off, so out of curiosity I started shooting ... everything was within 1 degree F,,, about one degree above the wall temperature in the shade ... which was the same as ambient.. 86F

Couldnt even find a temp rise on a lug.. or anywhere inside it, not even on the wires,, but then again they are 'insulated.


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RE: breaker temperature

cappo, I have no idea how this goober could possibly interpret UL489 to mean this. 40 deg C is the ambient air temp standard for testing.

Here is the text:

Temperature Testing
The UL 489 Standard allows for two types of
ratings. Standard circuit breakers cannot exceed
a maximum of 50C temperature rise at the wire
terminal connection at 100%current in 40C open
air. 100% rated circuit breakers may have a
temperature rise of 60C at the wire terminal
connection in the smallest allowable enclosure if
the circuit breakers are connected with wire rated
at 90C wiring insulation sized to the 75C chart
(Table 310-16, National Electric CodeNEC).
The ANSI C37 Standard requires a maximum of
55C temperature rise at 100% in the smallest
enclosure and a maximum of 85C temperature
rise on the contacts.


Here are a few good links your friend can browse:

http://ecmweb.com/mag/electric_sizing_circuit_breaker/

http://ecatalog.squared.com/pubs/Circuit Protection/Low Voltage Power Circuit Breakers/Masterpact NT UL 1066-ANSI Circuit Breakers/0613DB9902.pdf


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RE: breaker temperature

As usual the inspector only got part of the story correct.


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RE: breaker temperature

Everyone here talks about the temp rating of the breaker/terminals. What your not taking into account is that the outside-of-the-breaker temp is an "insulated" temp. The temp INSIDE the breaker. If the outside temp is 104F the inside temp could be much higher...


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