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Does back-feeding a low voltage dry type distribution transformer 15kVA or larger void the transformer's UL label?

Published date: 02 June 2020

Is it recommended to back-feed a low voltage dry type distribution transformer, 15kVA or larger, or will it void the transformer's UL label?

Product Line:
LV Transformers

Product Features


Square D does not label its low voltage dry type distribution transformer`s terminals as primary or secondary, so backfeeding is not a violation of UL. The terminals are labeled as high voltage (H`s) or low voltage (X`s).
In the event that the primary voltage is identical to that of the secondary, the primary is marked high voltage (HV) and the secondary is marked low voltage (LV).

Square D does not recommend backfeeding transformers due the high inrush currents developed and the upstream protection tripping due to the inrush. There are precautions to be observed in backfeeding.


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