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How do you size a circuit breaker or fusible switch for the primary or secondary of a transformer?

FA91626

29 September 2021

Issue:
How to select and size the Transformer Overcurrent Protection (OCP)

Product Line:
LV Transformers

Environment:
Applies to all SquareD/Schneider Electric Transformers

Cause:
Similar to other Electrical loads, Transformers often require Overcurrent Protection on the Secondary and/or Primary

Resolution:

Reference the National Electrical Code (NEC) Table 450-3(b) along with the transformer`s Full Load Amperage (FLA or full load current) on the primary and secondary, and whether primary only or both primary and secondary OCP will be provided.

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