mstrlucky74
Senior Member
- Location
- NJ
Was watching a Mike Holt video today and he states that when sizing conductors under 100a you use the 60 degree column. Is this true for THHN? That's rated for 90 degree .....that's why I ask. Thanks
Under 100a & 60 degree column
- Thread starter mstrlucky74
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Post the video..
What he stated is true,.,..... even for THHN.....
under the right conditions......
however, with most things Code, there is a "Page 2" or, in your case, the next segment of the video....
THere are also conditions where you can terminate that conductor at it's 75? rating on a less than 100 amp circuit... or even it's 90? rating..
The key is "termination limitations".... no doubt later explained by Mike.
Play the entire video and/or look at 110.14
under the right conditions......
however, with most things Code, there is a "Page 2" or, in your case, the next segment of the video....
THere are also conditions where you can terminate that conductor at it's 75? rating on a less than 100 amp circuit... or even it's 90? rating..
The key is "termination limitations".... no doubt later explained by Mike.
Play the entire video
and/or look at 110.14
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I agree with Gus. If the termination temperature of the lugs or whatever are not known then mike holt is correct but if they are known and are 75C rated then things change. We are limited to the weakest link in the connection.
kwired
Electron manager
- Location
- NE Nebraska
As mentioned 60C is the rule if the equipment is not otherwise marked. Most equipment today is marked for 75C and you generally only need to watch out for needing to use 60C if you are dealing with existing older equipment.
While true for supply-end distribution equipment, one has to be careful regarding load and circuit devices... some wall switches and receptacles, for example, are not marked or are only rated 60?C. Termination limitations apply to both ends of the circuit conductors.
kwired
Electron manager
- Location
- NE Nebraska
True, one doesn't generally have to worry about that with 15 -30 amp devices as the small conductor ampacity limitations of 240.4(D) take care of that most of the time, but over 30 amps is where you are more likely to run into this problem. That said I can't recall ever seeing what is usually 50 or 60 amp rated devices, if not 50 or 60 it is usually 100 or more, that are marked with 75C.
- Location
- Illinois
- Occupation
- retired electrician
The video in question is not available...it was his live streaming of the production his calculation DVD program. It is not posted anywhere for viewing. The program will be available for purchase after it is completed.
- Location
- Illinois
- Occupation
- retired electrician
The 90? ampacity can be used for ampacity adjustment or correction, but the final ampacity cannot exceed the value in the 60? column if the equipment is rated at 60?C.
jumper
Senior Member
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- 3 Hr 2 Min from Winged Horses
mstrlucky74
Senior Member
- Location
- NJ
what if the term temp is rated for 90 degre, which many are? Do you use the. 90 degree column? Thanks
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mstrlucky74
Senior Member
- Location
- NJ
Good point. What if one end is rated for 75 and the other is 60, what do you use? The lower I assume.
edit: I saw the video posed above. ... Disregard question.
jxofaltrds
Inspector Mike®
- Location
- Mike P. Columbus Ohio
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- ESI, PI, RBO
I think that he said be careful later on. That was when the terminals were NOT mark. I believe that he explained it that way.
kwired
Electron manager
- Location
- NE Nebraska
Not much in the below 600 volt world has 90C temp rating. Some lugs have 90C rating but the equipment they are attached to does not have 90C rating so that still puts you back to lower temp. Many neutral and EGC bars in panelboards are 90C but that is about it. We often don't get to use that higher temp rating because the device at the other end of the conductor is not 90C, or in the case of service/feeders, we may actually reduce the conductor size because the neutral only carries imbalanced current, and temp rating kind of just gets lost in those applications though it could apply. The EGC is not sized the same way as other conductors and temp rating just isn't a part of that process.
mstrlucky74
Senior Member
- Location
- NJ
Great info, thanks. So if a dist panel feeds(via. Breaker) another dist panel( to a main breaker) you are saying that usually the breakers won't be rated for 90 degree? Or instead of a MCB say it's a MLO.
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When discussing panelboards, there are none even tested to 90?C under UL certifications. Even 100%-rated assemblies are only tested to 75?C, but instructions require using 90?C-rated conductors. (disclaimer: that I'm aware of)
FWIW, you can use 90?C conductors at their 90?C rating, but you must use a transition enclosure (aka terminal box) completely separate from the panelboard. General consensus is the transition must be at least 4' of conductor away from the panelboard. The "transition" box must contain all 90?C or greater rated equipment, including wires from the panelboard. In the case of 75?C-rated equipment at both ends of the circuit, a transition would be required at both ends.
kwired
Electron manager
- Location
- NE Nebraska
Termination (splicing) devices used in that junction box also would need to be rated 90C.
kwired
Electron manager
- Location
- NE Nebraska
Main lugs alone may be rated 90C, but the bus they attach to probably is not. You do see circuit breakers typically in larger frame sizes that have lugs marked AL9CU - which means it is a 90C lug that accepts aluminum or copper, but the assembly they are attached to (the breaker) will have a 75C marking elsewhere that is the general rating of the breaker itself, the lugs are actually second party components which is why they are marked 90C. If they were used without the breaker they possibly could be used at their 90C rating, depending on what they are attached to.
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