What to check before ordering
If you want 120 V for general receptacles rather than control, you almost always want 480 to 208Y/120 three phase instead, because that gives you 120 V line to neutral on three phases rather than one small single phase circuit.
Current at each rating
Three phase full load current on both sides of a 480 V to 120 V transformer. The higher voltage side always carries less current for the same kVA.
| kVA | 480 V side | 120 V side |
|---|---|---|
| 15 | 18.0 A | 72.2 A |
| 30 | 36.1 A | 144 A |
| 45 | 54.1 A | 217 A |
| 75 | 90.2 A | 361 A |
| 112.5 | 135 A | 541 A |
| 150 | 180 A | 722 A |
| 225 | 271 A | 1,083 A |
| 300 | 361 A | 1,443 A |
| 500 | 601 A | 2,406 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 120 V
A step down transformer with a 4 to 1 ratio. Control power. A single 120 V circuit taken off a 480 V feed for contactors, relays, instrumentation and a service receptacle. Most units for this conversion fall in the 0.5 to 15 kVA range.
How many amps does a 480 V to 120 V transformer draw
It depends on the kVA. At 100 kVA the 480 V side carries about 120 amps and the 120 V side about 481 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
If you want 120 V for general receptacles rather than control, you almost always want 480 to 208Y/120 three phase instead, because that gives you 120 V line to neutral on three phases rather than one small single phase circuit.