maxpaxr
Member
- Location
- Morristown,Tn,USA
When sizing the branch circuits for more than one motor, using THHN. Do I use the 75 degree column as stated in 110.14 (C) for my ampacitance, or use the 90 degree column.
You use 90C for derating and 75C for final ampacity.
Could I also add.............I would have to look for the post which brought this to my attention..........but there where different ampacities for thhn in wet or dry locations?
From what I see of it...............
Lets say you did 125% of the largest then added the additional motors at 100%.......and came up with 27.5 amps. (and the actual continuous load wasn't over 24 amps for 80 % to protect the breaker......but just for #'s sake).
The 90 degree column shows the 10's rated for 40 amps.......however........ because of the equipment, you could only size those conductors to carry 30 amps.
If you had those 10's in a conduit with other conductors...if your total number of conductors in that conduit was 7-9 then you would derate from the 90 degree column at 70% which would now rate the 90 degree's (40) to be 28 amps.
(now my question)
Would you be allowed to put the 28 amp rated wire on a 30 amp breaker because of the next size higher over current protection.........or because of the 60 degree showing 30 would you have to go for the 8's at 40 amp????
Thank you...hope my lack of an answer and my proposed question made sense.
However if there would be 10-20 conductors in the conduit.......... you could use the 8's which would get rated at 50% of 55.......which would be 27.5 amps .............????
Next higher breaker should make the install ok at 30 amps correct.
You could protect the #10 motor feeder with an ampacity of 28 with a 40A c/b in this case, per 430.62(A).
About the 90 degree column...The wire in that column with that insulation has ampacities as listed. However because of the heat generated around the wire and the connections to the equipment, 100 amp and under have to apply for that wire size in the 60 degree column
and 800 amp and under have to apply for the wire size in the 75 degree column.
Unless the terminations are listed for use with 75 deg conductors. In that case you can use the ampacity from the 75 degree column for equipment rated 100Amps or less.
Just curious, where did the 800Amp come from?