Electrical
Derating — Electrical
01 — Definition
Bringing an electrical component's rated capacity down to a safe working level. The basic rule: a continuous load should not exceed 80% of the breaker's or the cable's rated capacity. A 16 A breaker therefore carries no more than 12.8 A continuously, and a cable rated 20 A goes no higher than 16 A in a bundle or conduit.
02 — In the field
The 80% rule is no excess of caution: it is what the US NEC explicitly requires for a continuous load. A lighting dimmer rack pulling 15.5 A continuously on a 16 A circuit will end up tripping the breaker within hours, as the breaker heats up. Design to 80%.