Question

Question: what size conductors do i need for a 225kva three phase transformer on the primary side = 480 @ 270 amps - secondary = 208y/120 @ 625 amps - i feel like im doing something wrong

Answer 1

Primary Side (480V, 270A) Determine the current capacity required: 270A Assuming a voltage drop of 2%, we can use the following formula:

Conductor size (kcmil) = (Current x Distance x Voltage drop) / (Voltage x 95)

Assuming a distance of 100 feet:
Conductor size (kcmil) = (270A x 100ft x 0.02) / (480V x 95)
Conductor size (kcmil) = 27 kcmil
Secondary Side (208Y/120V, 625A) Determine the current capacity required: 625A Again, assuming a voltage drop of 2%:
Conductor size (kcmil) = (Current x Distance x Voltage drop) / (Voltage x 95)
Assuming a distance of 100 feet:

Conductor size (kcmil) = (625A x 100ft x 0.02) / (208V x 95)

Conductor size (kcmil) = 150 kcmil

Recommendation

Based on these calculations, you will need the following conductor sizes for a 225kVA three-phase transformer:

Primary Side (480V, 270A)

27 kcmil

Secondary Side (208Y/120V, 625A): 150 kcmil Flag for review

Answer 2

Primary Side (480V, 270A) Determine the current capacity required: 270A Assuming a voltage drop of 2%, we can use the following formula:

Topic: 225kva transformer feeders