I wondering if I did this calc. correctly. I'm installing a new VFD which will be used to drive 1-50 hp, 480v, 3ph cooling tower motor, and 1-15 hp, 480v, 3ph cooling tower motor. The 15 hp motor is going to be used as backup in case the 50 hp motor fails.
FLA for 50 hp = 65A
FLA for 15 hp = 21A
Wire size:
(65*1.25) = 81.25A
Choose #4 conductors (85A ampacity)
OCPD min:
65*1.75 = 113.75A
OCPD max:
65*2.25 = 146.25A
Choose 3P125A breaker feeding motors.
But in this case I have to ensure only one motor running at once. Is this correct? Anyone size the wire and OCPD for two motors running as a worst case scenerio?
Please comment away. Thanks forum
FLA for 50 hp = 65A
FLA for 15 hp = 21A
Wire size:
(65*1.25) = 81.25A
Choose #4 conductors (85A ampacity)
OCPD min:
65*1.75 = 113.75A
OCPD max:
65*2.25 = 146.25A
Choose 3P125A breaker feeding motors.
But in this case I have to ensure only one motor running at once. Is this correct? Anyone size the wire and OCPD for two motors running as a worst case scenerio?
Please comment away. Thanks forum