johnweaver
Member
Can anyone Help?
What size inverse time circuit Bkr. for this feeder supplying the following motors on a 480 volt three phase delta system?
One 15 hp, two 10 hp, one 75 hp @ 15 minuite intermittent duty.
I have done it this way, am I wrong?
75 hp Full load amps = 96
96 amps x .85 (intermittent duty cycle art-430.22E)x 250% (inverse time Bkr.Art-430.52)
96 x .85 = 81.6 x 2.50 = 204 amps
Then take 204 amps and add the full load currents of all other motors.
204 amps plus
15 hp = 21 amps
10 hp = 14 amps
10 hp = 14 amps
Add these all up and you get 253 amps
with a feeder I cant go up in bkr. size so I have to step down to a 250 amp bkr. (Art-240 overcurrent protection)
Is any of this right? Thanks John
What size inverse time circuit Bkr. for this feeder supplying the following motors on a 480 volt three phase delta system?
One 15 hp, two 10 hp, one 75 hp @ 15 minuite intermittent duty.
I have done it this way, am I wrong?
75 hp Full load amps = 96
96 amps x .85 (intermittent duty cycle art-430.22E)x 250% (inverse time Bkr.Art-430.52)
96 x .85 = 81.6 x 2.50 = 204 amps
Then take 204 amps and add the full load currents of all other motors.
204 amps plus
15 hp = 21 amps
10 hp = 14 amps
10 hp = 14 amps
Add these all up and you get 253 amps
with a feeder I cant go up in bkr. size so I have to step down to a 250 amp bkr. (Art-240 overcurrent protection)
Is any of this right? Thanks John
