Branch Circuits

What a branch circuit is — and where it starts

The NEC defines a branch circuit as the conductors between the final overcurrent device protecting the circuit and the outlets it supplies. That boundary matters: the instant you cross from the downstream side of the last breaker or fuse to the first outlet or load, you are in branch-circuit territory and Article 210 applies. Everything between the service equipment and that final overcurrent device is a feeder, governed by Article 215.

Journeyman exam questions on branch circuits almost always start by testing whether you can draw that line correctly. A circuit with two panelboards in series has a feeder feeding the second panel and branch circuits leaving it — the location of the last overcurrent device is what decides which rules apply.

Types of branch circuits

Article 210 recognizes four branch-circuit types, and knowing them by name helps on exam questions that ask which rules apply:

• General-purpose branch circuit — serves two or more outlets for lighting and appliances. The standard residential 15- and 20-amp circuits that serve living areas fall here.
• Appliance branch circuit — supplies one or more outlets that are intended only for appliances. Lighting outlets are not permitted on these circuits. The kitchen small-appliance circuits described below are a specific required form of appliance branch circuit.
• Individual branch circuit — supplies only a single piece of utilization equipment. A dedicated circuit for a clothes dryer, range, or air conditioner is an individual branch circuit, and it must be sized for the load it serves.
• Multiwire branch circuit (MWBC) — uses two or more ungrounded conductors that share a common neutral, each connected to a different leg of the supply so the neutral carries only the unbalanced current. In practice, a 240/120-volt circuit with two hots and one shared neutral is the common dwelling form. Recent editions require that a multiwire branch circuit be controlled by a single multi-pole disconnect, so all conductors of the circuit open together.

Standard branch-circuit ratings

Section 210.3 lists the allowable ratings for branch circuits that serve two or more outlets: 15, 20, 30, 40, and 50 amperes. A circuit at any of those ratings can supply multiple outlets. Individual branch circuits — those that serve only a single load — are not limited to that list and can be any size needed for the equipment.

These minimum conductor sizes come from 310.12 for dwelling units and the ampacity tables for other occupancies. Always verify against the termination temperature rating of the equipment — most residential panels list 60°C or 75°C terminals, which controls which column of the ampacity table you use.

Required branch circuits in a dwelling unit

The NEC does not leave it to the designer to decide whether certain circuits exist. Section 210.11 mandates specific branch circuits in every dwelling unit:

• Small-appliance circuits (210.11(C)(1)): At least two 20-ampere branch circuits must supply the receptacle outlets in the kitchen, dining room, pantry, and similar areas. These circuits may not serve lighting outlets or other loads, and they must be 20-ampere rated (12 AWG conductors minimum).
• Laundry circuit (210.11(C)(2)): At least one 20-ampere branch circuit is required to supply the laundry receptacle outlet. This circuit may not serve other outlets (unless the laundry area is also used as a living space in specific dwelling types).
• Bathroom circuit (210.11(C)(3)): At least one 20-ampere branch circuit must supply the bathroom receptacle outlet(s). That circuit may serve more than one bathroom, or it may be dedicated to a single bathroom — but if it serves only that bathroom's receptacles, it can also serve other outlets within that same bathroom.

These are minimums. An exam question may ask what the code requires, not what a good design would add. Knowing that the small-appliance circuits must be 20-ampere, must supply only those areas, and that at least two are needed is the core fact to lock in.

Branch-circuit conductors and overcurrent devices must also account for continuous loads — any load expected to run for three or more hours must have the conductor and breaker sized at 125 percent of that load. That rule from 210.19 and 210.20 applies at the branch-circuit level the same way it does to feeders.