Have always used the NEC 75 C wire table amp ratings for specifications -- this prevents problems with installation of under rated conductors 75 C instead of 90 C and installed connectors not rated for 90 C. Electrician Contractor asked if conductors and panel/disconnect connectors rated at 90 C are there any reason why not to use other than what I stated above. Answer?
75 c or 90 c wire use
- Thread starter eutaw42
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ron
Senior Member
- Location
- New York, 40.7514,-73.9925
Re: 75 c or 90 c wire use
Although a termination may be listed for 90 deg as an individual termination, they must be tested as a 90 deg termination within the equipment they are used for. I do not think ANY panelboard, switchboard, switchgear, disconnect, stater etc manufacturer test at higher then 75 deg. So the termination and associated conductor insulation must be considered in the tested configuration, 75 deg. or less
[ December 10, 2003, 10:04 PM: Message edited by: ron ]
Although a termination may be listed for 90 deg as an individual termination, they must be tested as a 90 deg termination within the equipment they are used for. I do not think ANY panelboard, switchboard, switchgear, disconnect, stater etc manufacturer test at higher then 75 deg. So the termination and associated conductor insulation must be considered in the tested configuration, 75 deg. or less
[ December 10, 2003, 10:04 PM: Message edited by: ron ]
pierre
Senior Member
- Location
- Westchester County, New York
Re: 75 c or 90 c wire use
I have (unofficially) spoken to several manufacturers about this topic. Their general feeling is that with such a high percentage of electrical failures occurring at terminations, they do not want to 'add' to that by designing terminations for 90 degree C. I also believe that $ has a little to do with it. As I see it, conductors are ahead of equipment as far as temperature ratings.
Pierre
I have (unofficially) spoken to several manufacturers about this topic. Their general feeling is that with such a high percentage of electrical failures occurring at terminations, they do not want to 'add' to that by designing terminations for 90 degree C. I also believe that $ has a little to do with it. As I see it, conductors are ahead of equipment as far as temperature ratings.
Pierre
ryan_618
Senior Member
- Location
- Salt Lake City, Utah
Re: 75 c or 90 c wire use
What about terminations such as wire nuts, receptacles, switches, terminal strips, split-bolts, etc... 75 degrees?
What about terminations such as wire nuts, receptacles, switches, terminal strips, split-bolts, etc... 75 degrees?
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: 75 c or 90 c wire use
Thanks, Steve. I knew of that requirement, and wanted to show it to someone else yesterday. But I couldn't find it.
Thanks, Steve. I knew of that requirement, and wanted to show it to someone else yesterday. But I couldn't find it.
- Location
- Illinois
- Occupation
- retired electrician
Re: 75 c or 90 c wire use
Steve,
110.14(C)(1)(a)(3) permits the use of 75?C wire ampacities if the equipment is maked for such use. Many small breakers are marked to permit the use of the 75?C ampacity. The box of wire nuts that I have here are listed for use at 105?C. Standard switches and receptacles (30 amps or less) don't matter because 240.4(D) restricts the OCPD rating for #10 and smaller to the 60?C ampacity.
Don
Steve,
110.14(C)(1)(a)(3) permits the use of 75?C wire ampacities if the equipment is maked for such use. Many small breakers are marked to permit the use of the 75?C ampacity. The box of wire nuts that I have here are listed for use at 105?C. Standard switches and receptacles (30 amps or less) don't matter because 240.4(D) restricts the OCPD rating for #10 and smaller to the 60?C ampacity.
Don
Re: 75 c or 90 c wire use
Don:
I did know that the 75 C rating is allowed if the terminations are identified for that temp. However, I assumed the items Ryan mentioned wouldn't have a listed temp. rating. I didn't realize wire nuts had a listed temp. rating (other than 60 C). This does make sense so they can be used in wiring compartments of luminaires which often require 90 C wire.
Steve
Don:
I did know that the 75 C rating is allowed if the terminations are identified for that temp. However, I assumed the items Ryan mentioned wouldn't have a listed temp. rating. I didn't realize wire nuts had a listed temp. rating (other than 60 C). This does make sense so they can be used in wiring compartments of luminaires which often require 90 C wire.
Steve
- Location
- Massachusetts
Re: 75 c or 90 c wire use
I have also installed larger switch gear with 100% rated breakers and 90C terminations.
This would be where the service conductors tie into the main breaker.
I have also installed larger switch gear with 100% rated breakers and 90C terminations.
This would be where the service conductors tie into the main breaker.
klm0824
Member
- Location
- Baton Rouge, LA
Re: 75 c or 90 c wire use
Typically, you don't see 90C terminations until you hit medium voltage gear (see NEC 110-40). It is always the lowest rated device that dictates the ampacity you have to use.
I am still looking for someone to interpret 110.14(C): Conductors with temperature ratings higher than specified for terminations shall be permitted to be used for ampacity adjustment, correction, or both.
I used to think it meant I could start the derating from the 90C ampacity, but the final ampacity couldn't be more than the 75C ampacity. But, we have had many discussions about this, and now I am not sure.
I think we had a topic on this under the calcs forum, but I couldn't find it.
Typically, you don't see 90C terminations until you hit medium voltage gear (see NEC 110-40). It is always the lowest rated device that dictates the ampacity you have to use.
I am still looking for someone to interpret 110.14(C): Conductors with temperature ratings higher than specified for terminations shall be permitted to be used for ampacity adjustment, correction, or both.
I used to think it meant I could start the derating from the 90C ampacity, but the final ampacity couldn't be more than the 75C ampacity. But, we have had many discussions about this, and now I am not sure.
I think we had a topic on this under the calcs forum, but I couldn't find it.
Re: 75 c or 90 c wire use
With regard to the comment about 90degC rated cable and 100% rated breakers, 100% rated breakers DO NOT have 90degC terminals.
They have 75degC terminals.
When a 100% breaker is applied it must be installed in an enclosure that it is listed to be used with, it will have a solid state trips unit, and, instead is using the 125% of the continuous load plus 100% of the non-continuous load to size the cable, it's 100% + 100%. As such it is possible to reduce the size of the cable (based upon 75degC of course) as you don't have to include the extra 25% which saves on cable cost, but you also may be able to apply a smaller frame breaker, again, a cost savings. BUT, the cable must be a 90degC rated cable.
With regard to the comment about 90degC rated cable and 100% rated breakers, 100% rated breakers DO NOT have 90degC terminals.
They have 75degC terminals.
When a 100% breaker is applied it must be installed in an enclosure that it is listed to be used with, it will have a solid state trips unit, and, instead is using the 125% of the continuous load plus 100% of the non-continuous load to size the cable, it's 100% + 100%. As such it is possible to reduce the size of the cable (based upon 75degC of course) as you don't have to include the extra 25% which saves on cable cost, but you also may be able to apply a smaller frame breaker, again, a cost savings. BUT, the cable must be a 90degC rated cable.
- Location
- Massachusetts
Re: 75 c or 90 c wire use
The one I am familiar with is a Square D 3000 amp 480 volt breaker.
Yes it had electronic trip unit.
The wires did not terminate directly to the breaker they terminated to bus bars that in turn went to the breaker.
It was a while ago but I am fairly certain it the specs claimed 100% rated with 90C terms.
I may be mistaken and will try to find the paperwork on it.
The one I am familiar with is a Square D 3000 amp 480 volt breaker.
Yes it had electronic trip unit.
The wires did not terminate directly to the breaker they terminated to bus bars that in turn went to the breaker.
It was a while ago but I am fairly certain it the specs claimed 100% rated with 90C terms.
I may be mistaken and will try to find the paperwork on it.
pierre
Senior Member
- Location
- Westchester County, New York
Re: 75 c or 90 c wire use
From the UL White Book - General Information for Electrical Equipment.
Distribution and Control Equipment Terminations
Some distribution and control equipment is marked to indicate the required temperature rating of each field-installed conductor. If the equipment, normally intended for connection by wire sizes within the range 14-1 AWG, is marked "75C" or "60/75C", it is intended that 75C insulated wire may be used at full 75C ampacity. Where the connection is made to a circuit breaker or switch within the equipment, sucn a circuit breaker or switch must also be marked for the tmperature rating of the conductor.
Pierre
From the UL White Book - General Information for Electrical Equipment.
Distribution and Control Equipment Terminations
Some distribution and control equipment is marked to indicate the required temperature rating of each field-installed conductor. If the equipment, normally intended for connection by wire sizes within the range 14-1 AWG, is marked "75C" or "60/75C", it is intended that 75C insulated wire may be used at full 75C ampacity. Where the connection is made to a circuit breaker or switch within the equipment, sucn a circuit breaker or switch must also be marked for the tmperature rating of the conductor.
Pierre
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: 75 c or 90 c wire use
I agree with Roger?s comment. HOWEVER, that works only if the conductor is rated for 90C (i.e., is one of the types listed at the top of the 90C column). This distinction is part of the discussion in another current thread.
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