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13800 GY/7970 V to 480Y/277 V transformer
A step down transformer with a 28.75 to 1 ratio. A distribution primary used by a number of utilities and by industrial plants that distribute internally at 13.8 kV. Common on campuses, refineries and larger manufacturing sites.
What to check before ordering
13800 volts is close enough to 13200 that most manufacturers cover both from one design with full capacity taps. Ask whether the unit you are quoted is a 13200 build on a tap or a dedicated 13800 build, because it changes where the taps leave you.
Current at each rating
Three phase full load current on both sides of a 13800 GY/7970 V to 480Y/277 V transformer. The higher voltage side always carries less current for the same kVA.
| kVA | 13800 GY/7970 V side | 480Y/277 V side |
|---|---|---|
| 15 | 0.6 A | 18.0 A |
| 30 | 1.3 A | 36.1 A |
| 45 | 1.9 A | 54.1 A |
| 75 | 3.1 A | 90.2 A |
| 112.5 | 4.7 A | 135 A |
| 150 | 6.3 A | 180 A |
| 225 | 9.4 A | 271 A |
| 300 | 12.6 A | 361 A |
| 500 | 20.9 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 13800 GY/7970 V to 480Y/277 V
A step down transformer with a 28.75 to 1 ratio. A distribution primary used by a number of utilities and by industrial plants that distribute internally at 13.8 kV. Common on campuses, refineries and larger manufacturing sites. Most units for this conversion fall in the 150 to 2500 kVA range.
How many amps does a 13800 GY/7970 V to 480Y/277 V transformer draw
It depends on the kVA. At 100 kVA the 13800 GY/7970 V side carries about 4.2 amps and the 480Y/277 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
13800 volts is close enough to 13200 that most manufacturers cover both from one design with full capacity taps. Ask whether the unit you are quoted is a 13200 build on a tap or a dedicated 13800 build, because it changes where the taps leave you.