For a 480V primary / 240 secondary/ 120V Center tap (High Leg) transformer, what is the percentage allowed for the 120V single phase loads?

Issue:
Is there any way to increase the 5% loading restrictions for Delta High leg , center tapped transformers?

Product Line:
LV Dry Type Transformers

Environment:
Application

Cause:
Specification Clarification

Resolution:
The 5% limitation rating is the same across all KVA sizes. The Center Tap is on the Center coil, and the idea is not to burn the coil open by excessive heat through the Center Coil's winding, which carries both Single and Three Phase loads.

Hypothetically, a lightly loaded , or oversized KVA Transformer , would be able to withstand more loading on the Center Tap, but there is no Chart, or factor, indicating what would be "SAFE".

The 5% loading specification is stated as to not take any chances speculating about higher percentages based on loading , or oversizing the KVA of the Transformer.

For example:
3.5 KVA is needed for 120V loads using a 45KVA EX45T6HCT transformer . 5% allows for only 2.25KVA loading for 120V V. A 75KVA EX75T6HCT transformer would be necessary to safely provide 5% for the 120V load capacity.
The EX75T6HCT Transformer would need to be used and can meet the 3.5KVA requirement for 120V, since it's 5% rating is 3.75 KVA .

Released for: Schneider Electric Canada