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480 V three phase to 208Y/120 V three phase transformer
A step down transformer with a 2.31 to 1 ratio. The most common step down in North American commercial buildings. A 480 V service feeds motors and rooftop units, and this transformer creates the 208Y/120 panel that runs receptacles, lighting and office equipment.
What to check before ordering
208Y/120 gives you 120 V line to neutral for receptacles and 208 V line to line for larger single phase loads. It is a four wire system, so the transformer needs a grounded wye secondary and a neutral brought out.
Current at each rating
Three phase full load current on both sides of a 480 V three phase to 208Y/120 V three phase transformer. The higher voltage side always carries less current for the same kVA.
| kVA | 480 V three phase side | 208Y/120 V three phase side |
|---|---|---|
| 15 | 18.0 A | 41.6 A |
| 30 | 36.1 A | 83.3 A |
| 45 | 54.1 A | 125 A |
| 75 | 90.2 A | 208 A |
| 112.5 | 135 A | 312 A |
| 150 | 180 A | 416 A |
| 225 | 271 A | 625 A |
| 300 | 361 A | 833 A |
| 500 | 601 A | 1,388 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 three phase to 208Y/120 V three phase
A step down transformer with a 2.31 to 1 ratio. The most common step down in North American commercial buildings. A 480 V service feeds motors and rooftop units, and this transformer creates the 208Y/120 panel that runs receptacles, lighting and office equipment. Most units for this conversion fall in the 15 to 300 kVA range.
How many amps does a 480 V three phase to 208Y/120 V three phase transformer draw
It depends on the kVA. At 100 kVA the 480 V three phase side carries about 120 amps and the 208Y/120 V three phase side about 278 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
208Y/120 gives you 120 V line to neutral for receptacles and 208 V line to line for larger single phase loads. It is a four wire system, so the transformer needs a grounded wye secondary and a neutral brought out.