Feeder wire size and minimum ampacity
Feeder conductors must have an ampacity at least equal to the larger of the noncontinuous load plus 125% of the continuous load, or the maximum load after adjustment and correction factors.
What the code requires
Section 215.2 sets the minimum size of feeder conductors, such as the wires from a main panel to a subpanel. The ampacity must be at least the larger of two values: the noncontinuous load plus 125% of the continuous load, or the maximum load once the code's adjustment and correction factors are applied. Terminations must also comply with 110.14(C).
Under 215.2(B), the feeder's grounded conductor (usually the neutral) may not be smaller than the equipment grounding conductor size required by 250.122. Where grounded conductors are run in parallel, the 250.122(F) parallel-run rule does not apply to them. Under 215.2(C), a feeder that carries the total load of service conductors rated 55 A or less must have at least the ampacity of those service conductors.
On the job
- Run both checks and size to whichever result is larger: 125% of the continuous load plus the noncontinuous load, or 100% of the load after adjustment and correction.
- Older plans may cite the 2020 numbers 215.2(A)(1)(a) and (b), (A)(2) and (A)(3); in the 2023 code these are 215.2(A)(1), (A)(2), (B) and (C). The 2020 rules for feeders over 1000 V, formerly 215.2(B), are now in Part III of new Article 235.
Exceptions that matter
- Where the assembly, including its overcurrent devices, is listed for operation at 100% of its rating, the feeder may be sized at 100% of the load.
- A run between separately installed pressure connectors may be sized at 100% of the continuous and noncontinuous load, as long as that run does not extend into the supply or load enclosure.
- Grounded conductors that do not connect to an overcurrent device may be sized at 100% of the continuous and noncontinuous load.
Related sections
- NEC 215.3
- NEC 110.14(C)
- NEC 210.19: Branch-circuit wire size and minimum ampacity
- NEC 310.12: Sizing service wires for a house: the 83% rule
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