Consider again the 3-k VA, single-phase, 480-V to 120-V step-down transformer of the previous example.
Assume that the input wire is No. 14 AWG copper with THW insulation, and that it is protected by a 15-A circuit
breaker. The circuit breaker clearly is too large to serve
as the sole protection for the transformer. But, the 15 A
circuit breaker is less than 250% of the transformer full load
current.