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Code Q&A

Jun 13, 2007 7:47 PM, By Mike Holt

Q. When a lighting and appliance panelboard is fed from the secondary of a 3-phase transformer, is the panelboard required to have a main breaker installed in it?

panelboards supplied through a transformer

A. No. Lighting and appliance branch-circuit panelboards supplied from a transformer, as permitted in 240.21(C), must have overcurrent protection for the panelboard on the secondary side of the transformer. The required overcurrent protection can be in a separate enclosure ahead of the panelboard, or it can be in the panelboard [408.36(A), 408.36(A) Ex. 1, and 408.36(D)].

Exception: A panelboard supplied by a 2-wire system or a 3-wire, delta/delta-connected, 3-phase system, is considered protected by the primary protection device when installed in accordance with 240.4(F) and 240.21(C)(1).

Note: A lighting and appliance branch-circuit panelboard is one with more than 10% of its overcurrent protection devices protecting “lighting and appliance branch circuits,” which are 30A or less circuits with neutral connections [408.34(A)].