Branch-Circuit Ratings, the 125% Continuous-Load Rule, and Receptacle Ratings

Every branch circuit has a rating (its overcurrent device), and the code has firm rules about how much load you can put on it — especially for continuous loads that run a long time.

1. The 125% continuous-load rule

A continuous load is one whose maximum current runs for 3 hours or more. (CEC Art. 100) Because conductors and breakers heat up under sustained current, the code makes you oversize for it:

• Conductors: minimum ampacity ≥ 125% of the continuous load (plus 100% of noncontinuous), before adjustment/correction. (CEC 210.19(A)(1))
• Overcurrent device: rating ≥ noncontinuous load + 125% of the continuous load. (CEC 210.20(A))

Example: a 16 A continuous load → 16 × 1.25 = 20 A, so it needs a 20 A circuit.

Exception: if the assembly (including the OCPD) is listed for 100% operation, you may use 100% instead of 125%. Most standard gear is not, so plan on 125%.