jojo
Member
- Location
- Philippines
- Occupation
- Electrical Engineer
Hello guys, let me take your stand on this. I noticed in some designs that OCPD rating for a fire pump on the normal side is different on the the generator/emergency supply side. As an example, a 250Hp fire pump, 460V. Its LRA per NEC Table 430.251(B) is 1825 Amperes; its FLA is 302 Amperes per NEC Table 430.250.
To size its conductor ampacity, we calculate it as 1.25 times the fire pump FLA (302A x 1.25= 377A) ~ 400A ampacity.
To size its OCPD, we size it based on the locked-rotor current of the fire pump per NEC 695.4 (B)(1). So for a 250Hp fire pump motor, its OCPD rating would be 2000A.
What I notice is the OCPD rating on the fire pump's emergency/generator side; which is sized at 2.5 times fire pump's LFA (302A x 2.5 = 755A ~ 800A OCPD). Any idea the emergency side is size that way? Is it because there's a limitation on the generator side during motor starting? I'm confuse. Thanks in advance guys.
To size its conductor ampacity, we calculate it as 1.25 times the fire pump FLA (302A x 1.25= 377A) ~ 400A ampacity.
To size its OCPD, we size it based on the locked-rotor current of the fire pump per NEC 695.4 (B)(1). So for a 250Hp fire pump motor, its OCPD rating would be 2000A.
What I notice is the OCPD rating on the fire pump's emergency/generator side; which is sized at 2.5 times fire pump's LFA (302A x 2.5 = 755A ~ 800A OCPD). Any idea the emergency side is size that way? Is it because there's a limitation on the generator side during motor starting? I'm confuse. Thanks in advance guys.