New garage wiring must meet local building codes as well as National Electric Code. Garage wiring is no more difficult than interior house wiring, but there are a few differences you'll want to know about before you get started. Simple garage wiring must still meet code requirements. Keeping it simple means not adding more than you need or beyond what is required.
National Electric Code Basic Requirements.
Basic garage wiring requires three outlets to meet National Electric Code (NEC) requirements. The NEC calls light fixtures and receptacles "outlets." A convenience receptacle powers extension cords while a receptacle on the ceiling provides a place to plug in a garage door opener. A switched light fixture provides light to the garage.
Ground fault circuit interrupter (GFCI) receptacles protect against electric shocks in damp places or places where the possibility of contact with water exists, which includes garages, and the NEC requires GFCI receptacles for garage wiring.
The light provided on a garage door opener does not count as the required light fixture unless it is possible to turn it on and off without operating the garage door opener.
The interior garage lighting fixtures must be controlled by switches at each door with the exception of the overhead door. Adding a light switch near the overhead door won't add significantly to the garage wiring cost and is a good idea. You can control the interior lights from two locations with three-way switches. Installing switches at more locations requires an additional four-way switch for each additional location. Doors that exit the garage must each have their own convenience outlet outside and an exterior light.
Convenience receptacles and door opener receptacles should be GFCI-type receptacles. You can add GFCI protection for the lighting circuits by extending the wiring from the line terminals on the GFCI outlets.
Another option for GFCI protection uses a GFCI circuit breaker instead of the GFCI outlets, which provides protection for every receptacle and light circuit connected to the circuit breaker. You'll have to apply the supplied stickers indicating the receptacles, fixtures and switches are GFCI protected.
Wire the garage using sheathed cable in 14 gauge for 15 ampere circuits and 12 gauge for 20 ampere circuits. The cable runs up and down the inside faces of studs but does not cross between them unless the walls will be enclosed. On the ceiling, run cables along ceiling joists the same way. You can also run cables along wall top plates or alongside 2-by-4s that span ceiling joists. Staple cables to the centre of studs and joists. If you have to drill a hole, put it in the centre of the framing member.
Plastic wiring boxes simplify installation. After stripping the cable sheathing, you just push the cable into the box through the cable holes in back.
Building Permit Considerations
Building permits are required, and you'll have to submit a plan for the wiring when you apply for yours. Talk to the code enforcement agency first for local requirements. If you need additional help, your local home centre may have experts who can help you choose the right materials. Put a plan together that meets all the local code requirements, and present it when applying for your building permit. Include all the fixtures, switches and receptacles on the plan. Inspectors dislike surprises and won't be happy if they arrive to find you've performed work that wasn't in the plan submitted with the application. Neat, careful wiring that follows the plan leads to inspections that pass. Inspectors want to see the rough wiring before you close in any walls with drywall or other materials and before you install the fixtures, switches and receptacles.