Feeders

A feeder is any circuit conductor between the service equipment and the final branch-circuit overcurrent device. In practical terms, the wire running from your main panel to a sub-panel in the garage is a feeder. Article 215 tells you how to size it. Section 215.2(A)(1) establishes the core sizing rule: the feeder conductor ampacity must be at least 125 percent of the continuous load plus 100 percent of the noncontinuous load, based on the terminal temperature rating per 110.14(C). Alternatively, per 215.2(A)(2), the ampacity after all correction and adjustment factors must be at least 100 percent of the total load. You must satisfy both calculations and use whichever requires the larger conductor. The informational note to 215.2(A)(4) recommends — but does not mandate — that feeder conductors be sized so voltage drop does not exceed 3 percent, and that the combined voltage drop of feeder plus branch circuit does not exceed 5 percent. While this is only a recommendation, many inspectors and engineers treat it as a practical design target, and exam questions frequently test it. The feeder neutral must be sized per 220.61 to carry the maximum unbalanced load but must never be smaller than the equipment grounding conductor required by 250.122. Feeder taps — where you tap off a feeder without overcurrent protection at the point of the tap — are governed by the tap rules in 240.21(B), including the 10-foot tap rule, the 25-foot tap rule, and the outside feeder tap rule. These tap rules are among the most heavily tested topics on electrician licensing exams.