wye start delta run 350hp motor.

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Mporter4

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I have been asked to install a used air compressor.
350 hp
480v 3-phase
395 fla
12 lead

The compressor is supplied with a nema-5 and nema-6 starter and all required controls.ie ol's timers,etc.
The calculations I have done are as follows:
circuit breaker = 600 amp (414 fla x 150%=621)
conductor size= 700kcmil or parrallel 350's
conduit size = 2-2".

I also looked at section 440.32 and found a 72% derating factor. Does this apply?
SEE ATTACHMENT.
 
Mporter4 said:
I have been asked to install a used air compressor.
350 hp
480v 3-phase
395 fla
12 lead

The compressor is supplied with a nema-5 and nema-6 starter and all required controls.ie ol's timers,etc.
The calculations I have done are as follows:
circuit breaker = 600 amp (414 fla x 150%=621)
conductor size= 700kcmil or parrallel 350's
conduit size = 2-2".

I also looked at section 440.32 and found a 72% derating factor. Does this apply?
SEE ATTACHMENT.
Click to expand...
414 amps x 1.25 = 518 amps requires 900 kcm 75C or 2 300 kcm 75C.
If you use 2 conduits no derating is required per 310.15(B)(2)(a).
 
I used the fla x 125%.and the 90 deg. chart. thanks for the correction.
Also how did you figure the parrallel conductor size?
 
Mporter4 said:
I used the fla x 125%.and the 90 deg. chart. thanks for the correction.
Also how did you figure the parallel conductor size?
Click to expand...
Take the 518 amps(414 amps x 1.25 = 518 amps) and divide by 2.
518 amps/2 = 259 amps. Look in the table 310.16 under 75C for a conductor
that has at least 259 amp capacity which is 300 kcm = 285 amps.
 
You need to run 6 wires from the stater to the motor if this is a wye start, delta run set-up. You size each of the conductors at 58% of the motor full load current. See 430.22(C). In this case each conductor would be sized for ~240 amps. Six 250 kcmil in two conduits would do the job.
Don
 
wye-delta

wye-delta

don_resqcapt19 said:
You need to run 6 wires from the stater to the motor if this is a wye start, delta run set-up. You size each of the conductors at 58% of the motor full load current. See 430.22(C). In this case each conductor would be sized for ~240 amps. Six 250 kcmil in two conduits would do the job.
Don
Click to expand...

Don, Agree.
And for supply conductors to the controller, 300 kcmil in seperate conduits ??
(414 x 1.25 / 2 )
 
Augie,
You are correct. The section that I cited requires that the conductors on the line side of the controller be sized based on the full load current of the motor. I don't see anything that says you don't apply the 125% to the line side conductors.
Don
 
ptonsparky said:
I have not done a motor of this size so I am curious if the 150% breaker will hold on start. I know the current is reduced with this starting method just wondering how much and for how long.
Click to expand...

I have (in the far past) used a manual wye/delta starter to start a 200HP 480V motor on a vacuum pump.
It was kinda like shifting from second gear to third on a hot-rod car.
Pull her into second (low voltage), wind her up and then slam it into third (high voltage).
It was all done manually and by "ear".
Kinda scary now when I think of it.:)

steve
 
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