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Section 230.90 is the requirement for overcurrent protection for services.
Subsection 230.90(A) implies that the overcurrent device installed in service equipment really provides only overload protection. Its maximum size is not to be greater than the allowable ampacity of the conductor.
Because the service overcurrent device is necessarily at the load end of the service conductors (the service conductors are defined as ending at the service disconnecting means), this device cannot provide short-circuit or ground-fault protection for those conductors. The service overcurrent device generally cannot interrupt faults on its supply side and generally cannot sense such faults. However, overload protection can function at any point in a conductor if it is in series with all the load on the conductor.
© Hughes Associates,Inc. 2012