Overcurrent Protection, Branch Circuits, and Feeders
Matching conductors to protection
Article 240 requires each conductor to be protected at its ampacity. Section 240.4(D) sets hard caps regardless of ampacity: 14 AWG copper at 15 A, 12 AWG at 20 A, and 10 AWG at 30 A for most circuits. Section 240.4(B) allows the next higher standard rating only when the ampacity does not match a standard size (240.6), the device is 800 A or less, the ampacity does not correspond to a standard rating, and the circuit does not supply multioutlet receptacles for cord-and-plug loads. Taps under 240.21 are the classic exception, and their length, ampacity, and enclosure rules must all be satisfied.
Branch circuits
Know the required circuits: a 20 A laundry branch circuit, two or more 20 A small-appliance circuits for the kitchen, and a 20 A bathroom circuit. Receptacle placement (210.52), lighting outlets (210.70), GFCI protection (210.8), and AFCI protection (210.12) are asked in nearly every exam. Feeder and service calculations live in Article 220 - general lighting demand factors, appliance demand, and the optional method for dwellings.
Traps
- Making a breaker larger to stop tripping is never the answer; fix the load or the conductor.
- Voltage drop recommendations (3% branch, 5% total) are informational, not enforceable.
- A 240.4(B) next-size-up answer is wrong if the load is a multioutlet receptacle circuit.
Worked example
A feeder with a calculated load of 52 A and 6 AWG copper at 60 C (55 A ampacity) is protected by a 60 A breaker. Section 240.4(B) permits this because 55 A is not a standard rating, 60 A is the next standard size, and the device is under 800 A - assuming the circuit does not serve multioutlet receptacles.