Branch Circuits vs Feeders: How to Tell Them Apart on the Exam

The Article 100 definitions

• Branch circuit: the circuit conductors between the final OCPD protecting the circuit and the outlet(s).
• Feeder: all circuit conductors between the service equipment, the source of a separately derived system, or another power source, and the final branch-circuit OCPD.

Picture the panel. The breakers in the panel are the final OCPDs. Conductors going OUT of those breakers to receptacles, lights, motors = branch circuits. Conductors coming IN to that panel from another panel or the service = feeders.

Different articles, different rules

• Article 210: branch circuits. Continuous load 80% rule, GFCI/AFCI, dwelling unit required circuits.
• Article 215: feeders. Feeder ampacity calculations, neutral feeder sizing.
• Article 220: calculations for both. The shared section that handles load determination.

The 125% / 100% sizing rules

Both branch circuits and feeders have a 125% rule for continuous loads, but the feeder rule has additional layers.

• Branch circuit (210.20): conductor ampacity ≥ 125% of continuous load + 100% of non-continuous load.
• Feeder (215.2): conductor ampacity ≥ 125% of continuous load + 100% of non-continuous load. Plus apply demand factors per Article 220.

The bonus on feeders: demand factors from 220.42 (general lighting), 220.55 (range), 220.54 (dryer), and others reduce the calculated feeder load below the connected load. Branch circuits don’t use demand factors because they serve specific outlets.

The neutral on a feeder

215.7 lets you size the feeder neutral for the maximum imbalance between the line conductors. For three-phase systems with mostly balanced loads (motors, three-phase lighting), the neutral can be smaller than the phase conductors. For dwellings with lots of single-phase loads, the neutral is typically the same size.