Overcurrent Protection
The ampacity of conductors is shown in Table 310.15(B)(16)
and accompanying notes of the
National Electrical Code
.
This ampacity should be observed in sizing overload protection for
the circuit.Lighting is considered a continuous load. NEC 210.20
requires that for continuous loads, the rating of the overcurrent
device shall be at least 125% of the actual lighting load. For example,
if the actual lighting load is 18 amps, then the minimum breaker
size would need to be at least 1.25 x 18 amps = 22.5 amps. Since
that is not a standard size, the next higher breaker size of 30
amps would be used.
When sizing overcurrent protection, the device closest to
the load should be the smallest size. Devices should increase in
size toward the service disconnect.
For example, a 10
amp fuse might be used in the pole base where the branch circuit breaker
is 20 amps, and the main breaker is a 60 amp circuit breaker.