Planning a dwelling's electrical system

Lesson 1 calculated how large a house's service must be. Before any cable is pulled, the electrician (or designer) must also decide where every outlet, switch and light goes, how they are grouped into circuits, where the panel sits, and how cables will run through the structure. Good planning produces an installation that meets the code, suits the people who live in the house, is easy to inspect and maintain, and leaves room for the electric vehicles, heat pumps and solar panels that homeowners increasingly add. This lesson covers reading residential drawings, walking through a house room by room, grouping outlets into circuits, building a panel schedule, and planning for the future.

Reading residential electrical drawings

For new houses, the architect's floor plans usually include an electrical layout, or the electrician prepares one for the permit. It uses standard symbols drawn on the floor plan:

Curved dashed lines connect switches to the lights they control. A home run arrow with circuit numbers shows that the cable from that outlet returns to the panel on those circuits. Notes on the drawing specify mounting heights, special receptacles (for example a 240 V receptacle for a range or a USB receptacle), and equipment supplied by others (a furnace, a heat pump, a hot tub).

Many smaller jobs have no drawings beyond a sketch, and the electrician lays out the work with the homeowner on site, marking box locations on the studs during a walk-through. Either way, the layout is checked against the code requirements for receptacle spacing, required circuits and protection before roughing in.

A room-by-room walk-through

Planning room by room ensures nothing is missed. For each room the questions are: how will it be used, where will furniture and appliances go, which outlets does the code require, and what does the owner want beyond that?

• Entrances and hallways: a switched light at each entrance and exterior door, three-way switching at each end of halls and stairways, receptacles in longer halls, doorbell and smoke alarm locations.
• Living and bedrooms: receptacles meeting the spacing rule (Lesson 5), a switched light or switched receptacle, extra receptacles where televisions, computers and bedside lamps will sit, possibly data and coaxial outlets.
• Kitchen: counter receptacles at the required spacing on the required circuits, receptacles for the refrigerator, microwave and dishwasher, the range or cooktop and oven circuits, lighting under cabinets and over the island, a range hood (Lessons 5 and 6).
• Bathrooms: a receptacle near the basin with ground-fault protection, a light and exhaust fan, often a heated floor.
• Laundry: a receptacle for the washer, a dryer circuit, sometimes a utility sink.
• Basement and utility areas: the panel, furnace or heat pump, water heater, sump pump, lighting at stairs and in each area, receptacles for future finishing.
• Garage and exterior: receptacles with ground-fault protection, lighting at doors and the garage door opener, an EV charger or its future circuit, outdoor receptacles at the front and back, exterior lighting.

Grouping outlets into circuits

Once outlets are placed, they are assigned to circuits. Good practice, beyond code minimums:

• Separate required circuits first: kitchen counter, bathroom, laundry, and individual appliance circuits (Lessons 5 and 6).
• Do not put all of a floor's lighting on one circuit: if it trips, the occupants should not be in darkness. Lights and receptacles of a room are often on different circuits.
• Limit the number of outlets per circuit so that typical loads fit comfortably: many electricians keep general circuits to about 8 to 12 outlets, and fewer where heavy plug-in loads are expected, such as home offices with computers and space heaters.
• Group outlets that are physically close, to keep cable runs short and voltage drop low.
• Spread 120 V circuits evenly across the two legs of the panel so the neutral current and the loading on each leg stay balanced (Lesson 3).

In Canada, the CEC limits the number of outlets on a 15 A branch circuit in a dwelling (Rule 8-304 sets a general maximum of 12 outlets per circuit), and requires AFCI protection for most 125 V, 15 A and 20 A receptacle circuits in dwelling units.

The panel schedule

A panel schedule lists every circuit: its number, description, breaker size and poles, the conductor size, the protection type (standard, AFCI, GFCI or dual function), and the estimated load. It is used to choose the panel size (number of spaces), to balance the legs, and later as the basis of the panel directory required on the panel door.

Routing cables through the structure

Before roughing in, the electrician plans cable routes: up from the basement or panel through the plates of interior walls, along joists, and into each box. The goals are short runs, few crossings of exterior walls and fire separations, protection from nails and screws, and access for future work.

• Interior walls are preferred for vertical runs; exterior walls are full of insulation and, in cold climates, have air and vapour barriers that must be kept continuous around boxes.
• Holes are bored near the centre of studs and joists and kept within the limits the building code sets for structural members.
• Fire separations, such as walls and ceilings between an attached garage and the house, or between dwelling units, must not be weakened; penetrations are sealed with listed firestopping.
• Space is left in ceilings and basements for future runs, and a spare conduit from the panel to the attic or to the garage is a cheap addition that saves much work later.

In Canadian cold-climate construction, boxes in exterior walls and insulated ceilings are usually vapour-barrier boxes (with a flange to which the polyethylene air and vapour barrier is sealed), so that warm, moist indoor air cannot leak into the wall cavity and condense.

Planning for the future

Houses are being electrified: gas furnaces replaced by heat pumps, gas ranges by induction, cars by electric vehicles, plus solar panels and home batteries. An installation planned today should anticipate them (Lessons 8 and 10):

• Service size: 200 A is now common for new single-family houses, and some designers specify more for all-electric homes, or plan load management instead (Lesson 10).
• Panel spaces: generous spare spaces and, where possible, two-pole spaces for future 240 V loads.
• Rough-ins: a 240 V circuit or conduit to the garage or driveway for an EV charger, to the range location even if a gas range is installed, and to the exterior where a heat pump might go; a conduit from the panel to the attic for future solar.
• Smart panels and load management devices that monitor and control circuits, allowing larger loads on a given service.