The 2005 NEC section 695.7 states that fire pump controller voltage shall not drop more than 15 percent below the normal controller rated voltage under motor starting conditions. I have been told that fire pump controllers for 460V motors are typically rated 460 / 480V. This would lead me to believe that I'd be okay with 391V (85% of 460V) at the controller, but I've also been told by others that I must go by the 480V rating for this calculation (85% = 408V). The motor will be rated for starting at 80% of 460V, so the driving factor will be voltage required at the controller for proper operation.
Typically, I'd just use the more conservative assumption, but in this case it makes a big difference (6 per phase 4/0 3/C versus 2 per phase 4/0 3/C cable, 450 ft).
Thanks for any help.
Typically, I'd just use the more conservative assumption, but in this case it makes a big difference (6 per phase 4/0 3/C versus 2 per phase 4/0 3/C cable, 450 ft).
Thanks for any help.