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 Canadian houses are wired with non-metallic sheathed cable, NMD90, which has two or three insulated copper conductors and a bare bonding conductor in a PVC jacket; armoured cable (AC90) is used where the cable may be exposed to damage. NMD90 must be supported within 300 mm of each box and at intervals of not more than 1.5 m, and protected where it passes through framing near the face of a stud or joist.

Wiring is planned so that circuits are logical and well labelled: 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.

The Canadian Electrical Code requires receptacles in finished rooms of a dwelling to be located so that no point along the floor line of any usable wall space is more than 1.8 m horizontally from a receptacle, measured along the wall. Wall spaces 900 mm or more wide count as usable, and doorways, fireplaces and similar openings break the wall. Hallways, bathrooms, kitchens and laundry areas have their own rules.

Kitchens

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

In Canada, counter work surfaces must have receptacles so that no point along the wall line of the counter is more than 900 mm from a receptacle, with at least one receptacle for each counter section 300 mm or more wide, and receptacles for islands and peninsulas. Counter receptacles are supplied either by 20 A circuits with 5-20R (T-slot) receptacles, or by 15 A split receptacles on multiwire circuits, and the code limits how many counter receptacles may share a circuit. A separate receptacle is required for the refrigerator, and dedicated circuits are typical for the dishwasher, microwave and range.

Bathrooms, laundry, outdoors and garages

• Bathrooms: at least one receptacle within 1 m of the washbasin, protected by a GFCI; receptacles must not be within a set distance of the bathtub or shower.
• Laundry: a receptacle for the washing machine, normally on its own circuit, plus a dryer circuit.
• Outdoors: at least one receptacle for a single dwelling, accessible from the ground, GFCI protected, with an in-use (bubble) cover where exposed to rain.
• Garages and carports: at least one receptacle for each car space (traditionally for block heaters), and some provinces and municipalities now require new houses to be ready for EV charging, with a circuit or conduit in place.

Number of outlets per circuit

The Canadian Electrical Code limits a 15 A general-purpose branch circuit to no more than 12 outlets (each receptacle or lighting outlet counts as one), which keeps circuits from being overloaded by many small loads. Kitchen counter circuits have their own, tighter limit.

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 travellers 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 even where the code does not demand it, because adding one later means fishing new cable. 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 tamper-resistant, with internal shutters that keep children from inserting objects into one slot. Outdoor receptacles and those in wet locations need weatherproof or in-use covers.

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.