How are fuses sized by?

Fuses are sized based on the electrical load they will protect, typically calculated using the continuous current rating of the circuit. The fuse's ampere rating should exceed the maximum expected load to prevent nuisance blowing while still being low enough to protect the wiring and equipment from overload or short circuits. Factors like ambient temperature, wire gauge, and the type of load (resistive or inductive) also influence fuse selection. Safety standards and codes, such as the National Electrical Code (NEC), provide guidelines for proper sizing.