What to check before ordering
Stepping up is electrically fine but the primary current is high, so the feeder and protection on the 208 V side are larger and more expensive than people expect. Check the existing service can carry it before ordering.
Current at each rating
Three phase full load current on both sides of a 208Y/120 V to 480 V transformer. The higher voltage side always carries less current for the same kVA.
| kVA | 208Y/120 V side | 480 V side |
|---|---|---|
| 15 | 41.6 A | 18.0 A |
| 30 | 83.3 A | 36.1 A |
| 45 | 125 A | 54.1 A |
| 75 | 208 A | 90.2 A |
| 112.5 | 312 A | 135 A |
| 150 | 416 A | 180 A |
| 225 | 625 A | 271 A |
| 300 | 833 A | 361 A |
| 500 | 1,388 A | 601 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 208Y/120 V to 480 V
A step up transformer with a 1 to 2.31 ratio. Running 480 V equipment in a building that only has a 208 V service. Typical when a tenant installs a large chiller, a lift or an EV charger in a building never wired for it. Most units for this conversion fall in the 15 to 225 kVA range.
How many amps does a 208Y/120 V to 480 V transformer draw
It depends on the kVA. At 100 kVA the 208Y/120 V side carries about 278 amps and the 480 V side about 120 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
Stepping up is electrically fine but the primary current is high, so the feeder and protection on the 208 V side are larger and more expensive than people expect. Check the existing service can carry it before ordering.