Q. What are the overcurrent protection requirements for panelboards?
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A. Each panelboard must be provided with overcurrent protection located within, or at any point on the supply side of, the panelboard. The overcurrent device must have a rating not greater than that of the panelboard, and it can be located within or on the supply side of the panelboard [408.36].
Exception No. 1: Individual overcurrent protection isn’t required for panelboards used as service equipment where the service disconnecting means consists of up to six circuit breakers mounted in a single enclosure in accordance with Sec. 230.71.
When a panelboard is supplied from a transformer, as permitted in Sec. 240.21(C), the overcurrent protection for the panelboard must be 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(B)].
Plug-in circuit breakers that are back-fed from field-installed conductors must be secured in place by an additional fastener that requires other than a pull to release the breaker from the panelboard [408.36(C)]. The purpose of the breaker fastener is to prevent the circuit breaker from being accidentally removed from the panelboard while energized, thereby exposing someone to dangerous voltage.
CAUTION: Circuit breakers marked “line” and “load” must be installed in accordance with listing or labeling instructions [110.3(B)]; therefore, these types of devices must not be back-fed.
