Services, Feeders and Branch Circuits
What the exam targets
Article 230 (services), Article 215 (feeders), Article 210 (branch circuits), and Article 220 load calculations. Expect questions on continuous versus noncontinuous loading, the dwelling small-appliance/laundry/bathroom rules, receptacle spacing, and the distinction between service point, service equipment, feeder, and branch circuit.
Concepts to own
- A continuous load operates 3 hours or more. Conductors and overcurrent devices: 125% of continuous plus 100% of noncontinuous (210.19(A), 210.20(A), 230.42).
- The overcurrent device protects the conductor; the conductor's corrected/adjusted ampacity must carry the load, with the next standard size allowed only under 240.4(B).
- 210.11(C): a dwelling needs two 20 A small-appliance circuits in the kitchen, one 20 A laundry circuit, one 20 A bathroom circuit.
- 210.52 spacing: receptacle outlets arranged so no point along the wall is more than 6 ft from an outlet (12 ft maximum spacing), including wall spaces 2 ft or wider.
- Service-entrance conductors sized per 230.42 from Table 310.16, generally using the 75 °C column for terminations.
Traps
Applying 125% twice; using the 90 °C column; counting the grounded conductor as current-carrying on a 120/240 V multiwire circuit; confusing "service" with "feeder" in a detached-building question; counting a bathroom receptacle as part of the kitchen small-appliance circuits.
Worked example
A 40 A continuous load: 40 × 1.25 = 50 A. Conductors must have an ampacity of at least 50 A and the overcurrent device is 50 A. 8 AWG copper at 75 °C (50 A) is the minimum; 6 AWG at 75 °C (65 A) gives margin for ambient correction or voltage drop.