Question(1) of the week (for me anyway):
I looking for opinions (and the science/regulation/industry practices behind them). Probably lots of ways to attack this - likely most will work - I haven't settled on a good one. And I am missing some understanding - which I am working on.
The installation:
MCC is 480V, 3ph, Z grounded. Motor is 31FLA, 225LRA. Feeder length ~700 ft. Load is likely considered high starting torque.
My thinking: (I'm open to critique on this)
Normally I would size the conductors to no more than 5% at 115% FLA (for an sf of 1.15). For those that are even wondering, yes, also at least the minimum required by art. 430.
However, since this is a high starting torque load, I'm thinking maybe I should be sizing conductors to a specified Vd at starting current (locked rotor). If so, what to specify? I'm thinking the NEC spec for firepumps is a good place to start - no more than 15% (art 695.7) - but at the motor, not the controller.
Oh yeah, I not looking at this as a code issue. I expect to be over the minimums.
Any thoughts?
carl
I looking for opinions (and the science/regulation/industry practices behind them). Probably lots of ways to attack this - likely most will work - I haven't settled on a good one. And I am missing some understanding - which I am working on.
The installation:
MCC is 480V, 3ph, Z grounded. Motor is 31FLA, 225LRA. Feeder length ~700 ft. Load is likely considered high starting torque.
My thinking: (I'm open to critique on this)
Normally I would size the conductors to no more than 5% at 115% FLA (for an sf of 1.15). For those that are even wondering, yes, also at least the minimum required by art. 430.
However, since this is a high starting torque load, I'm thinking maybe I should be sizing conductors to a specified Vd at starting current (locked rotor). If so, what to specify? I'm thinking the NEC spec for firepumps is a good place to start - no more than 15% (art 695.7) - but at the motor, not the controller.
Oh yeah, I not looking at this as a code issue. I expect to be over the minimums.
Any thoughts?
carl