Transformer has been backfed
HPS does not recommend that transformers be backfed due to safety issues. The nameplate no longer matches the application and may violate electrical codes and common wiring practices. Backfed transformer are susceptible to high inrush currents, voltage unbalances and lower than expected output voltages.
| Check: | Solution: |
|---|---|
| Inrush current is causing nuisance tripping. | Size the fuse or breaker to the largest allowed by the local electrical code and use time delay fuses or high short circuit trip points on breakers. Replace with a step up transformer is problem persists. |
| Output voltage is lower than expected. | Windings are turns compensated to take into account the natural voltage drop which occurs in the wires. When a transformer is backfed, the voltage drop still occurs but the winding compensation works in reverse. If possible, use taps to adjust. Replace with a step up transformer if the problem persists. |
| Is the transformer a delta-wye transformer that is being backfed such that the wye becomes the primary. | This application is not suggested and involves the removal of ground straps which would violate the UL listing of the transformer. This must be replaced with a custom step up transformer. |