Very confused about 90 deg wire and derating

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Twophase said:
Won't fit in my conduits anyways, so looks like I'm going to go with 500 MCM..... And I need to review this stuff a little more
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Doesn't NEC 215.2(A)(1) require 750 MCM (377 x 1.25) if motor is a continuous load?
 
ramsy said:
Doesn't NEC 215.2(A)(1) require 750 MCM (377 x 1.25) if motor is a continuous load?
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No. Sizing of motor feeder conductors is per Art. 430. But the OP appears to be sizing branch circuit conductors in this instance.
 
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Twophase said:
Also, how is sizing and derating done for MV cable? There is no 75 deg column for MV cables (such as MV-105)
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That is because the insulation system for type MV-90 is rated for 90C and for type MV-105 it is rated for 105C.
 
ramsy said:
Doesn't NEC 215.2(A)(1) require 750 MCM (377 x 1.25) if motor is a continuous load?
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I agree with David. You don't need to "double dip" the 125% factors. A motor's circuit conductors must be 125% of FLA. A continuous load's conductors must be 125% of its rated current. Even if the motor runs continuously, we only apply the 125% to the FLA.
 
charlie b said:
Even if the motor runs continuously, we only apply the 125% to the FLA.
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Yes I see.
Art. 430 shows no reference to continuous loads. Art. 430.6 reference to 310.15(B) & (C) also avoids reference to continuous loads.

Art. 220.18(A) reference to motors also avoids continuous loads.
 
Derating is so for protecting the conductor insulation cracking and also reduces heat transferring to conduits
david luchini said:
No. Sizing of motor feeder conductors is per Art. 430. But the OP appears to be sizing branch circuit conductors in this instance.
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what is OP
 
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