Branch circuits and receptacles

Branch circuits are the final circuits from the panel to the lights, receptacles and appliances of the house. They are where most of an electrician's residential work happens, and where the code is most detailed, because they are what occupants touch every day. This lesson covers the kinds of branch circuit and their ratings, cable and wire sizes, the number and placement of receptacles, dedicated circuits for appliances, lighting outlets and switching, and receptacle types.

Kinds of branch circuit

Residential branch circuits fall into a few groups:

• General-purpose 120 V circuits, rated 15 A (14 AWG copper) or 20 A (12 AWG copper), supplying lighting and general receptacles.
• Small-appliance and kitchen counter circuits, which carry the heavy, intermittent loads of kettles, toasters and microwaves.
• Dedicated (individual) circuits supplying one appliance: refrigerator, dishwasher, washing machine, microwave, furnace, sump pump and so on.
• 240 V circuits for large appliances: range (commonly 40 A), dryer (30 A), water heater, baseboard heaters, heat pumps and air conditioners, EV chargers.
• Multiwire branch circuits: two ungrounded conductors from opposite buses sharing one neutral, for example to supply a split kitchen receptacle. The neutral carries only the difference of the two currents, saving a conductor, but the two hots must be on a two-pole breaker or handle-tied breakers so both are disconnected together.

The circuit rating is set by the overcurrent device, and the conductors must be protected by it. The small-conductor rule from ELEC-120 applies: 14 AWG copper on no more than 15 A, 12 AWG on 20 A and 10 AWG on 30 A, regardless of the higher ampacity of 90 °C insulation.

Cable and wiring practice

Most US houses are wired with non-metallic sheathed cable, type NM-B, which has insulated copper conductors and a bare equipment grounding conductor in a PVC jacket; type MC or AC cable or raceway is used where required for protection or by local amendments (some cities, such as Chicago, require conduit). NM cable must be secured within 12 in of each box and at intervals of not more than 4½ ft (334.30), and protected by steel plates where it passes through framing within 1¼ in of the edge (300.4).

Wiring is planned so that circuits are logical and well labeled: lights and receptacles of a room are often on different circuits, so a tripped breaker does not leave a room dark; high-load receptacles are spread across circuits; and 120 V circuits are balanced between the two buses (Lesson 3). The panel directory must identify every circuit clearly.

Receptacle spacing

Receptacles must be placed so that a lamp or appliance with a normal cord can reach one from anywhere along a wall, which discourages extension cords.

NEC 210.52(A) requires receptacles in habitable rooms of a dwelling so that no point along the floor line of any wall space is more than 6 ft from a receptacle, measured along the wall; in other words, receptacles at most 12 ft apart and within 6 ft of each doorway. Any wall space 2 ft or more wide counts, including space occupied by fixed panels of sliding glass doors. Hallways 10 ft or longer need at least one receptacle.

Kitchens

Kitchens have the most demanding requirements, because counters host many high-current appliances.

In the US, at least two 20 A small-appliance branch circuits must serve the kitchen, pantry, breakfast and dining room receptacles (210.11(C)(1)), and they may not serve other outlets. Countertop receptacles must be placed so that no point along the wall line is more than 24 in from a receptacle (210.52(C)), with every countertop space 12 in or wider served; island and peninsula requirements were revised in the 2023 NEC. Refrigerators may be on a small-appliance circuit or an individual 15 A or larger circuit; dishwashers and disposers are commonly on their own circuits, and all kitchen receptacles need GFCI protection (Lesson 7).

Bathrooms, laundry, outdoors and garages

• Bathrooms: at least one 20 A receptacle within 3 ft of each basin (210.52(D)), on a 20 A bathroom circuit that serves only bathroom receptacles (or one bathroom's entire load), GFCI protected.
• Laundry: a 20 A laundry circuit (210.11(C)(2)) with a receptacle for the washer, plus the dryer circuit.
• Outdoors: at least one receptacle at the front and one at the back of a one-family dwelling, accessible from grade and not more than 6½ ft above it (210.52(E)), GFCI protected, weather-resistant, with an in-use cover.
• Garages: at least one receptacle for each vehicle bay in the 2023 NEC, on a circuit serving only the garage receptacles, GFCI protected.

Number of outlets per circuit

The NEC does not limit the number of outlets on a dwelling general-purpose circuit. Instead, enough circuits must be provided for the calculated general lighting load: at 3 VA/ft², a 2400 ft² house has 7200 VA, which needs at least 7200/(120 × 15) = 4 circuits of 15 A, or 3 of 20 A (210.11(A)). Many designers limit circuits to 8 to 10 outlets as good practice.

Lighting outlets and switching

Every habitable room, bathroom, hallway, stairway, attached garage and outdoor entrance needs a lighting outlet controlled by a wall switch near the entrance (in living rooms, a switched receptacle may be accepted in place of a ceiling outlet). Stairways with six or more risers, and rooms with more than one entrance, commonly need switches at each end or entrance:

• A single-pole switch controls a light from one place.
• Two three-way switches control a light from two places: the supply goes to the common terminal of the first switch, two travelers connect the switches, and the common of the second switch feeds the light.
• Four-way switches inserted between the two three-ways add each further control location.

Smart switches, occupancy sensors and dimmers usually need a neutral at the switch box. Bringing a neutral to every switch location is therefore good practice, and the NEC has required it at most switch locations since 2011 (404.2(C)). Dimmers must be compatible with the lamps, especially LED lamps, and rated for the load.

Receptacle types

Receptacle configurations are standardized by NEMA (and in Canada by CSA, which uses the same configurations) so that a plug fits only a matching voltage and current rating:

• 5-15R: 15 A, 125 V, the ordinary duplex receptacle. 5-20R: 20 A, 125 V, with a T-shaped slot that accepts both 15 A and 20 A plugs.
• 14-30R: 30 A, 125/250 V, four-wire, for dryers. 14-50R: 50 A, 125/250 V, four-wire, for ranges and plug-in EV chargers.
• 6-20R, 6-30R and 6-50R: 250 V receptacles without neutral.

Older three-wire 10-30 and 10-50 receptacles, which use the neutral as the equipment ground, are no longer permitted for new installations; new dryer and range circuits use four-wire receptacles with a separate equipment grounding conductor.

Receptacles in dwellings must be listed tamper-resistant (406.12), with internal shutters, and receptacles in damp and wet locations must be listed weather-resistant (406.9), with in-use covers where exposed to rain.

Lesson 6 continues with the circuits for ranges, dryers, water heaters, pumps and other major appliances, and Lesson 4 covers how the cable and boxes for these circuits are installed.