What to check before ordering
Ask whether you need 240 V three phase delta or 240/120 V single phase, because they are different transformers. A 240 V delta secondary with a centre tap gives the high leg, which reads 208 V to ground and must not be used for 120 V loads.
Current at each rating
Three phase full load current on both sides of a 480 V to 240 V transformer. The higher voltage side always carries less current for the same kVA.
| kVA | 480 V side | 240 V side |
|---|---|---|
| 15 | 18.0 A | 36.1 A |
| 30 | 36.1 A | 72.2 A |
| 45 | 54.1 A | 108 A |
| 75 | 90.2 A | 180 A |
| 112.5 | 135 A | 271 A |
| 150 | 180 A | 361 A |
| 225 | 271 A | 541 A |
| 300 | 361 A | 722 A |
| 500 | 601 A | 1,203 A |
Nameplate full load current, computed from the standard three phase formula. Free to cite with a link to this page. For any rating not listed, use the kVA to amps calculator.
Common questions
What transformer do I need to go from 480 V to 240 V
A step down transformer with a 2 to 1 ratio. Feeding older equipment, shop tools and machinery built for 240 V from a 480 V service. Common in retrofits where the building service was upgraded but the machines were not. Most units for this conversion fall in the 15 to 150 kVA range.
How many amps does a 480 V to 240 V transformer draw
It depends on the kVA. At 100 kVA the 480 V side carries about 120 amps and the 240 V side about 241 amps. Current is kVA times 1000 divided by the voltage times the square root of three, so the higher voltage side always carries less current for the same kVA.
What should I check before ordering
Ask whether you need 240 V three phase delta or 240/120 V single phase, because they are different transformers. A 240 V delta secondary with a centre tap gives the high leg, which reads 208 V to ground and must not be used for 120 V loads.