Generally, the NEC requires coordination of wire ampacity with the rating of the overcurrent protective device feeding the wire. Wire ampacity cannot be smaller than the rating of the overcurrent protective device.
However, special cases exist where the "tap rule" modifies the above requirement, and overcurrent protective devices can be increased in size with respect to wire ampacity. For general applications, tap rules are specified in NEC section 240.21
For portable feeder applications in theatres and similar locations, the tap rules are specified in NEC sections 520.53(H)(3) and (4).
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