Neal Lewis Posted July 8, 2010 Report Posted July 8, 2010 100 amp service panel from the 1960's. 3 or 4 window A/c units were running constantly today: no other considerable draw. The main Square D breaker was 140 degrees and located in a basement that was probably 80 degrees today. No other outward signs of overheating. Is there some type of allowable limit for heat buildup? I did recommend a sparky take a look.
John Dirks Jr Posted July 8, 2010 Report Posted July 8, 2010 Corrosion where it attaches to the bus or at the main lugs can make it heat up. I suspect corrosion inside the breaker can do that too. Did you see any signs of corrosion in the panel?
Jim Katen Posted July 8, 2010 Report Posted July 8, 2010 100 amp service panel from the 1960's. 3 or 4 window A/c units were running constantly today: no other considerable draw. The main Square D breaker was 140 degrees and located in a basement that was probably 80 degrees today. No other outward signs of overheating. Is there some type of allowable limit for heat buildup? I did recommend a sparky take a look. That's a good question. I don't know the answer. I'd suggest dropping a line to Square D. They're very good about answering technical questions about their products. - Jim Katen, Oregon
Terence McCann Posted July 8, 2010 Report Posted July 8, 2010 Found this: 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 ratingââ¬â60°C or 75°C. The temperature rise at the circuit breaker terminals must not exceed 50°C above ambient per UL Standard 489. 50C = 122F + 80F = 202F. That's seems awfully hot. The complete PDF is here: http://ecatalog.squared.com/pubs/Circui ... DB0103.pdf
Marc Posted July 9, 2010 Report Posted July 9, 2010 A change of 50°C corresponds to 90° F. Ambiant of 80°F + delta 90°F= 170° F max. Marc
Terence McCann Posted July 9, 2010 Report Posted July 9, 2010 A change of 50°C corresponds to 90° F. Ambiant of 80°F + delta 90°F= 170° F max. Marc I don't follow you Marc. How did you end up with 50C = 90F? Me thinks you forgot to add 32° .
Marc Posted July 9, 2010 Report Posted July 9, 2010 I don't follow you Marc. How did you end up with 50C = 90F? Me thinks you forgot to add 32°. The 32 is added when you want the Farenheit equivalent of a temperature that is expressed on the Centigrade scale. In this case, it's not a temperature value that we are dealing with, it's a change in temperature. Marc
Terence McCann Posted July 10, 2010 Report Posted July 10, 2010 The 32 is added when you want the Farenheit equivalent of a temperature that is expressed on the Centigrade scale. In this case, it's not a temperature value that we are dealing with, it's a change in temperature. Marc Well I must be slow. The temperature rise at the circuit breaker terminals must not exceed 50°C above ambient per UL Standard 489. The variable is ambient, not 50C per se. 50C=122F. With the above statement they could have easily said: The temperature rise at the circuit breaker terminals must not exceed 122F above ambient per UL Standard 489. If your ambient is 80F and you shouldn't exceed 50°C above ambient doesn't that mean 50C ((°C x 1. + 32 = °F)= 122F + the ambient which is 80F? I'm getting the feeling I'm wrong but I don't see where.
Marc Posted July 10, 2010 Report Posted July 10, 2010 Let's say that the ambient temperature is 80 degrees Farenheit. What's the equivalent temperature in Centigrade? (80 -32) * (5/9) = 26.7 C The temperature rise at the circuit breaker terminals must not exceed 50°C above ambient which in our case is: 26.7 + 50= 76.7 C When we change back to Farenheit units, we get: (76.7 * (9/5)) + 32 = 170 F The difference between the two Farenheit temperatures is: 170 - 80 = 90 degrees. So, a delta 50C is equivalent to a delta 90F. Marc
Rocon Posted July 10, 2010 Report Posted July 10, 2010 Marc is correct on this. And just in case anyone is concerned it is also 350.15 K (kelvins). Just in the off chance that anyone at all wanted to know... LOL
Marc Posted July 10, 2010 Report Posted July 10, 2010 Uhhh, actually, the Kelvin unit is the same size as the Centigrade unit. Marc
Rocon Posted July 10, 2010 Report Posted July 10, 2010 In my best Monty Python accent... No it isn't. http://www51.wolframalpha.com/input/?i= ... Fahrenheit You were Right now you are wrong.
Marc Posted July 10, 2010 Report Posted July 10, 2010 They are the same size units, but their scales are displaced by 273.15 degrees for the purpose of.....never mind. Marc
Rocon Posted July 10, 2010 Report Posted July 10, 2010 In my best Monty Python accent... No it isn't. http://www51.wolframalpha.com/input/?i= ... Fahrenheit You were Right now you are wrong. That is what happens when it is 6:15 on a friday and I rush to turn off the computer. Marc you are still correct, hats off to you sir.
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