Need help with motor load question

[joemama]

Motor load feeder calculations


Question: service feeder multimotor connection

460v service

1ea 120v 19.92amp continuous duty motor
1ea 230v 33.2amp 5 min. intermitten duty motor
1ea 230v 23.24amp continuous duty motor
1ea 460v 22.41amp continuous duty motor
1ea 460v 11.62 5 min. intermitten duty motor
1ea 460v 43.16amp continuous duty motor

I would first convert all the amperage rating to va using their voltages perspectively
Apply the derating of 85% to the 5min intermitten duty motors
Apply 125% to the highest load rated moter

2390.4va @ 100% = 2390.4va
7636va @ 85% = 6490.6va
5345va @ 100% = 5345va
10308.6va @ 100% = 10308.6va
5345.2va @ 85% = 4543.42va
19853.6va @ 125% = 24817va

total va = 53895.02

53895va / 460v = 117 amps

 

[bphgravity]

Re: Need help with motor load question

I see one error.

The 3-phase loads need to be increased by 1.732. (ex: V x A x 1.732 = 3-phase va.)

 

[joemama]

Re: Need help with motor load question

Thanx

any idea where I should round off the numbers in respect to the Washington State test

+/- .5va

+/- .5 amp ?

 

[sparky9669]

Re: Need help with motor load question

When doing calculations you need to look at the voltage you are using. The NEC says to use 480/277, 120/240, and etc. in any calculation.

FYI, I have taken the test 3 times and have still not successfully passed.