Transformer OCP Calculations

[j_a_wolfe]

We have a 3 phase, 45kVa transformer being used to reduce 480V to 240V. The equipment to be run from the secondary is around 65A and is fused accordingly. The question we have is OCP and wire sizing. Do we need to calculate OCP for the maximum expected current or from the rated load?
Thanx,
Jim

 

[DetroitEE]

We have a 3 phase, 45kVa transformer being used to reduce 480V to 240V. The equipment to be run from the secondary is around 65A and is fused accordingly. The question we have is OCP and wire sizing. Do we need to calculate OCP for the maximum expected current or from the rated load?
Thanx,
Jim

Are you talking OCP and wire size for the primary or secondary? Is this transformer only serving this piece of equipment?

 

[ptonsparky]

Use Table 450.3(B) for protection of the transformer and 240.21 for protection of the conductors.