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

How can we help you today?

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.

Released for: Schneider Electric USA

Published on:9/22/2010Last Modified on:12/15/2025

Range:

Sealed General Purpose Transformers (Resin Encapsulated)

Range:

Sealed General Purpose Transformers (Resin Encapsulated)

Released for: Schneider Electric USA

Products

Support

Company

Quick Links

Partners

Sustainability

Events

Insights
opens new tab