I was walking through the big orange box yesterday and of course wondered to electrical section. I was looking at square d homeline breakers for upcoming job and decided to actually read what is on side of breaker. The 40 amp and up 2 pole breakers say for 75 c wire only. The 30 amp and under breakers says for 60/75C wire. Does anyone know why the 2 pole says 75C when NMB is rated for 60C?My understanding is if it says 75C only that means you cannot use 60C wire unless it is marked 60/75C. If put alot of these in but cant say i remember that 75C only rating being on breaker,but I don't sit there and read each one either. This probably sounds trivial but I'm still curious Any info would be appreciated
temperature rating on breaker
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ryan_618
Senior Member
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- Salt Lake City, Utah
Re: temperature rating on breaker
NMB is rated 90 degrees. See 334.80
NMB is rated 90 degrees. See 334.80
Re: temperature rating on breaker
That's the way the devices have been marked for some time now.Take a look at 2002NEC art 110-14(C)(1) Equipment provisions.
Also, when applying product marked with 75decC terminations with existing 60degC wire one always applies the wire still at 60degC.
The reason for these terminal markings is the way the breakers are UL tested, that the breaker will function correctly with that rated wire. If one were to apply 75degC rated wire at its 75degC with a 60degC rated device the heat generated by the wire would conduct itself into the device. A breaker would derate when that extra heat causes the thermal element to start to bend prematurely tripping even though the cable is not overloaded. A breaker with 60degC terminals expects to see 60degC rated wire.
That's the way the devices have been marked for some time now.Take a look at 2002NEC art 110-14(C)(1) Equipment provisions.
Also, when applying product marked with 75decC terminations with existing 60degC wire one always applies the wire still at 60degC.
The reason for these terminal markings is the way the breakers are UL tested, that the breaker will function correctly with that rated wire. If one were to apply 75degC rated wire at its 75degC with a 60degC rated device the heat generated by the wire would conduct itself into the device. A breaker would derate when that extra heat causes the thermal element to start to bend prematurely tripping even though the cable is not overloaded. A breaker with 60degC terminals expects to see 60degC rated wire.
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- retired electrician
Re: temperature rating on breaker
Don
Does the reverse apply? That is will the use of 60?C wire on a OCPD rated for 75?C conduct heat away from the breaker and let it carry more current before it trips?
Don
wirenut1980
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- Plainfield, IN
Re: temperature rating on breaker
Interesting question...I believe that the wire will conduct more current before the 75 deg C breaker trips than if it were connected to a 60 deg C breaker, which would result in a potentially unsafe condition for wire rated at only 60 deg C. I do not believe a 60 deg C wire would be completely protected by a 75 deg C breaker. But I could be wrong.
Interesting question...I believe that the wire will conduct more current before the 75 deg C breaker trips than if it were connected to a 60 deg C breaker, which would result in a potentially unsafe condition for wire rated at only 60 deg C. I do not believe a 60 deg C wire would be completely protected by a 75 deg C breaker. But I could be wrong.
Re: temperature rating on breaker
I'm just relating how I understand UL testing to be done. Testing must be do in accordance to an established standard. I do agree that the reverse is probably true but if one were to get technical, as if I understand you correctly, that applying wire rated 60degC means larger kcmil than with 75degC which means the wire absorbs more heat from the breaker. As such it would take more current to trip the breaker because the breaker is running cooler.
But when it gets down to it it?is like trying to spit hairs and making a mountain out of a mole hill.
If one take a look at all of the variables from the breaker calibration which is commonly +-10% thermally and +-20% magnetically, the exterior ambient temperature outside the enclosure where basement can be 55-60degF to locations that run significantly warmer, in addition to the interior enclosure temperatures that are affected by the loading of other breakers, etc., I believe that any issues when applying 60degC cable on a breaker rated for use with 75degC cable would be very minor.
I'm just relating how I understand UL testing to be done. Testing must be do in accordance to an established standard. I do agree that the reverse is probably true but if one were to get technical, as if I understand you correctly, that applying wire rated 60degC means larger kcmil than with 75degC which means the wire absorbs more heat from the breaker. As such it would take more current to trip the breaker because the breaker is running cooler.
But when it gets down to it it?is like trying to spit hairs and making a mountain out of a mole hill.
If one take a look at all of the variables from the breaker calibration which is commonly +-10% thermally and +-20% magnetically, the exterior ambient temperature outside the enclosure where basement can be 55-60degF to locations that run significantly warmer, in addition to the interior enclosure temperatures that are affected by the loading of other breakers, etc., I believe that any issues when applying 60degC cable on a breaker rated for use with 75degC cable would be very minor.
sandsnow
Senior Member
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- Southern California
Re: temperature rating on breaker
I can't answer your question completely. I can refer you here to the UL marking guide for circuit breakers: http://www.ul.com/regulators/circuit600.pdf
I can make some informed suppositions.
1. The breaker generated to much heat for a 60deg. conductor.
2. The manufacturer did not submit it for testing for use with a 60deg. conductor because 60deg conductors are all but obsolete except for existing installations.
I can't answer your question completely. I can refer you here to the UL marking guide for circuit breakers: http://www.ul.com/regulators/circuit600.pdf
I can make some informed suppositions.
1. The breaker generated to much heat for a 60deg. conductor.
2. The manufacturer did not submit it for testing for use with a 60deg. conductor because 60deg conductors are all but obsolete except for existing installations.
Re: temperature rating on breaker
If you follow the rules this should never happen.
Eg 1. Requirements for 100 amp load. If the breaker is rated at 60C(assume it is old) then you would have to choose either #2 or #1 under the 60C col.
If you choose #3 under the 75C col, even thought it is rated for 100 amps, the #3 being smaller in size and having more resistance, would heat up the 60C terminals and possibly damage the breaker or cause it to trip.
Using this example the rule says that even if you are using 75C conductor you must use the 60C col to select the proper size. In this case #2 or #1. It does not matter which insulation temp you use but the conductor rating must not exceed the rating determined by the lower temp, in this case the 60C rating.
If the breaker had been rated 60/75C you could have used the 75C rating.
[ December 20, 2004, 11:41 PM: Message edited by: bob ]
Temp
If you follow the rules this should never happen.
Eg 1. Requirements for 100 amp load. If the breaker is rated at 60C(assume it is old) then you would have to choose either #2 or #1 under the 60C col.
If you choose #3 under the 75C col, even thought it is rated for 100 amps, the #3 being smaller in size and having more resistance, would heat up the 60C terminals and possibly damage the breaker or cause it to trip.
Using this example the rule says that even if you are using 75C conductor you must use the 60C col to select the proper size. In this case #2 or #1. It does not matter which insulation temp you use but the conductor rating must not exceed the rating determined by the lower temp, in this case the 60C rating.
If the breaker had been rated 60/75C you could have used the 75C rating.
[ December 20, 2004, 11:41 PM: Message edited by: bob ]
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Re: temperature rating on breaker
This is a link to a Square D publication Wire Temperature Ratings and Terminations.
This is a link to a Square D publication Wire Temperature Ratings and Terminations.
sandsnow
Senior Member
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- Southern California
Re: temperature rating on breaker
Thanks for that Jim, that is a good explanation of everything
Re: temperature rating on breaker
Bob, You're right, if the rules are followed. My example was only to point out how the cable affects the breaker. Yes,I agree that a breaker with 60deg terminals when applied with 75degC rated wire the wire must be applied at 60degC.
However, when retrofitting to older 60degC which is commonly done, we agree that the wire must be applied still at 60degC. What this means is that the kcmil is larger for the 60degC wire than it would be if the wire were 75degC. As such the 60degC wire would have a lower temperature rise and would end up as a bigger heat sink for the breaker. Technically A breaker with 75degC terminals should run cooler when applied with 60degC rated wire than 75degC rated wire. As per my previous post there are so many variables from breaker calibration to ambient temperatures that applying 60degC wire with a OCPD that has 75deg terminals is a mute point.
Bob, You're right, if the rules are followed. My example was only to point out how the cable affects the breaker. Yes,I agree that a breaker with 60deg terminals when applied with 75degC rated wire the wire must be applied at 60degC.
However, when retrofitting to older 60degC which is commonly done, we agree that the wire must be applied still at 60degC. What this means is that the kcmil is larger for the 60degC wire than it would be if the wire were 75degC. As such the 60degC wire would have a lower temperature rise and would end up as a bigger heat sink for the breaker. Technically A breaker with 75degC terminals should run cooler when applied with 60degC rated wire than 75degC rated wire. As per my previous post there are so many variables from breaker calibration to ambient temperatures that applying 60degC wire with a OCPD that has 75deg terminals is a mute point.
Re: temperature rating on breaker
The marking on a breaker is either 60/75c or a straight 75c.
When marked with bothe ratings 60/75c is is to be used at 60c for less than 100 amps and for a Motor load it is rated 75c even if it is less than 100 amps...
110-14c is the key to selection of conductors and rating of terminals and breakers lugs
The marking on a breaker is either 60/75c or a straight 75c.
When marked with bothe ratings 60/75c is is to be used at 60c for less than 100 amps and for a Motor load it is rated 75c even if it is less than 100 amps...
110-14c is the key to selection of conductors and rating of terminals and breakers lugs
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