NEC 310.15(C)(1)

Isaiah

Senior Member
Location
Baton Rouge
Occupation
Electrical Inspector
I’ve got number 4, 3/C #12 AWG XHHW-2, 90 Degree C, in a RGS conduit.
These are for 3 phase, 460V induction motors at 12FLA each.
My understanding is the ampacity adjustment factor should be against the 30A, not against the 20A per 310.16 and 240.4(D).
So 4, 3phase motors x 12 current carrying conductors would mean an adjustment of 50% per 310.15(C)(1) or 15A per cable. Is this correct?


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infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
The 12A is nameplate FLA. not the FLC from 430.250
430.6 (IIRC) requires you to use the values from the tables, not the nameplate, for MCA and MOCPD calculations.
As Wayne stated you need to use the table values that's why I asked. Usually the marked current on the motor is less than what you need to use for your calculation so #12's @ 50% ampacity and times 125% may be too small.
 

Isaiah

Senior Member
Location
Baton Rouge
Occupation
Electrical Inspector
As Wayne stated you need to use the table values that's why I asked. Usually the marked current on the motor is less than what you need to use for your calculation so #12's @ 50% ampacity and times 125% may be too small.

That is correct, but there is no chance of ever replacing these motors with motors of higher ampacity
12 x 1.25 = 15
 
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