Code Q&A: Sizing Circuit Conductors for Individual Appliances
Q. What are the NEC branch-circuit rating requirements for individual appliances?
See answer below.
A. (A) Individual Circuits [Sec. 422.10]. The branch-circuit ampere rating for an individual appliance isn’t permitted to be less than the branch-circuit rating marked on the appliance [Sec. 110.3(B)]. The branch-circuit rating for motor-operated appliances must be in accordance with Sec. 430.6(A) and Sec. 430.22. A branch-circuit for an appliance that’s a continuous load must be rated not less than 125% of the marked ampere rating of the appliance [Sec. 210.19(A)(1)].
Let’s run through an example scenario based on these requirements.
Example: What’s the calculated load for conductor sizing for a 4,500W, 240V water heater?
Solution: I = P ÷ E = 4,500W ÷ 240V = 18.75A
Conductor Sizing = 18.75A × 125% = 23.44A
Answer: 10 AWG conductor [Table 310.15(B)(16)]
Branch circuits for household ranges and cooking appliances can be sized in accordance with Table 220.55 and Sec. 210.19(A)(3).
(B) Circuits Supplying Two or More Loads [Sec. 422.10(B)]. Branch circuits supplying appliances and other loads must be sized in accordance with the following:
- Cord-and-plug-connected equipment must not be rated more than 80% of the branch-circuit ampere rating [Sec. 210.23(A)(1)].
- Equipment fastened in place must not be rated more than 50% of the branch-circuit ampere rating, if the circuit supplies both luminaires and receptacles [Sec. 210.23(A)(2)].
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