NEC 310.15(C)(1)

[Isaiah]

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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[LarryFine]

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?

Correct, if I understand the question. You can start with the 90-deg amperage rating.

 

[Isaiah]

Correct, if I understand the question. You can start with the 90-deg amperage rating.

Thanks Larry


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[infinity]

These are for 3 phase, 460V induction motors at 12FLA each

How many HP? Is 12 amps from table 430.250?

 

[Isaiah]

How many HP? Is 12 amps from table 430.250?

The 12A is nameplate FLA. not the FLC from 430.250


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[wwhitney]

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.

Cheers, Wayne

 

[infinity]

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]

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

 

[don_resqcapt19]

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

The code is clear. If you want to do this, you will need a 90.4 written special permission.

 

[infinity]

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

Unfortunately the calculation cannot be performed with the nameplate value.

 

[Isaiah]

The code is clear. If you want to do this, you will need a 90.4 written special permission.

You’re right
I will inform the client - but he won’t be very happy


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