Feeders: Sizing
(215), Overcurrent Protection, Taps (240.21), and Outside Feeders to Other Buildings (225)
NFPA 70 National Electrical Code, 2023 edition · Reviewed 2026-09-21
A feeder runs from the service equipment (or the source of a separately derived system) to the final branch-circuit overcurrent device. The Florida DBPR blueprint lists Feeders as its own topic under Wiring and Protection (feeder load knowledge and calculations, grounded conductors and grounding/bonding, overcurrent protection), and the calculation items ask feeder load and conductor sizing directly. Everything below is the 2023 text (viewer pages in the source pack).
1. Sizing the feeder conductors — 215.2
(A) Ampacity ≥ the larger of:
- noncontinuous load + 125% of the continuous load (215.2(A)(1)) — before any adjustment/correction. Exceptions: an assembly (including the feeder OCPD) listed for 100% operation; separately installed pressure connectors rated for 100% at both ends; grounded conductors not connected to an OCPD may be sized at 100% (Exc. 3).
- the maximum load after ambient correction and bundling adjustment (215.2(A)(2)).
Also 110.14(C): the termination temperature limits the usable ampacity column.
(B) Grounded conductor: never smaller than the EGC Table 250.122 would require for the feeder OCPD (so a 200 A feeder's neutral is at least 6 AWG copper even with a tiny neutral load), and larger where 220.61 requires it. (C) A feeder that carries the entire load of a service of 55 A or less must have ampacity at least equal to the service conductors.
Informational Notes: 3% feeder / 5% total voltage drop (advisory); Annex D examples.
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