In general, distribution transformers can be reverse connected without de-rating the nameplate KVA capacity. However some precautions need to be taken for reverse connection of some smaller transformers. On Delta Transformers under 6kVA three phase and 3kVA single phase, there is a "turns ratio compensation" on the low voltage winding. When the input voltage, equal to the nameplate rated voltage, is connected to the low voltage winding, the output voltage will be slightly lower than the nameplate rating. When a three-phase transformer is reverse connected thus resulting in a Wye-Delta configuration, the neutral terminal must be isolated. Further, the reverse connected transformer may draw a higher inrush current during energization. Hence the sizing of the line fusing or circuit breaker may be affected.
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