If you're replacing an existing fixture, switch, or receptacle, there's usually no need to contact the building department. But when you run new electrical cable for new service, whether wiring several circuits or adding just one receptacle, be sure to work with a building inspector and comply with all local codes. We'll walk you through some of the most common general requirements for home electrical systems, plus offer some general how-to tips.
Professional electricians often refer to the National Electrical Code (NEC), a massive volume that describes national codes for residential and commercial wiring. You don't need to buy this book, but you may need to refer to a library copy from time to time.
Local building departments often modify the NEC, and you must satisfy those local codes. It's not unusual for adjacent towns to have very different codes; for instance, one may allow plastic boxes while another requires metal boxes. Have a local inspector approve your wiring plans before you begin work.
If existing wiring does not meet local codes, chances are that your building department will not require you to change the wiring. Usually only new work must be up to code. However, if the old wiring is unsafe, you should change it. Extensive remodeling also may require you to bring the entire house up to current codes.
Any plan, however simple or complex, must start with two considerations. First, make sure the new service doesn't overload a circuit. Second, see that all receptacles and appliances are safely grounded. Local codes probably require that switches and light fixtures also be grounded. Grounding protects against shock in case a wire comes loose or an appliance or device malfunctions. Check using a receptacle analyzer.
All receptacles and appliances must attach to a ground wire (or metal sheathing) that runs to the service panel. Check with local codes to determine the approved method.
A thick ground wire should emerge from the service panel and clamp tightly to a cold-water pipe or grounding rods driven into the ground outside the house.
Here are some of the most common general requirements for home electrical systems. Local building departments may have different demands.
Boxes: Plastic electrical boxes are common throughout much of the United States and Canada; some localities require metal boxes. Buy large boxes so wires aren't cramped. Attach them firmly to a framing member whenever possible or use remodel boxes that clamp to the wall surface.
Receptacles, fixtures, and appliances: New receptacles and appliances must be grounded. Fixtures and appliances should be approved by Underwriters Laboratories (UL).
Cable: Nonmetallic (NM) cable is the easiest to run and is accepted by most building departments. Wherever cable is exposed rather than hidden behind drywall or plaster, armored cable or conduit may be required.
Circuits: Most 120-volt household circuits are 15 amps, and all lights must be on 15-amp circuits. In kitchens and utility areas, 20-amp circuits may be required.
Wire size: Use 14-gauge wire for 15-amp circuits and 12-gauge wire for 20-amp circuits. Cable runs longer than 500 feet may need larger wire. Consult your building department.
Service panels: As long as you do not need to add a new circuit, your service panel, even if it is an old fuse box, is probably sufficient. If you add circuits, you may need to upgrade the panel or add a subpanel. Check with an inspector or professional electrician.
Some codes apply to the entire house; others apply to specific rooms. Here are some general guidelines. Local codes may vary. These requirements usually apply only to new installations—older wiring does not have to comply as long as it is safe. These requirements make good sense and are not overly strict. Wiring that does not meet these standards would be either awkward or unsafe.
Bedrooms, living room, dining room: Every room must have a wall switch located near the entry door that controls either a ceiling fixture or a switched receptacle. All ceiling fixtures must be controlled by a wall switch and not by a pull chain. Receptacles must be no more than 12 feet apart, and there must be at least one on each wall. If a section of wall between two doors is wider than 2 feet, it must have a receptacle. Light fixtures must be on 15-amp circuits. Usually receptacles are allowed to share a circuit with lights. But a heavy electrical user, such as a window air-conditioner or a home theater, may need to be on a dedicated circuit.
Hallways and stairways: All stairways must have a light fixture controlled by three-way switches at the bottom and top of the stairs. Hallways may also need a light controlled by three-way switches. A hallway longer than 10 feet must have at least one receptacle.
Closets: There should be at least one overhead light, controlled by a wall switch rather than a pull chain. The light must have a globe rather than a bare bulb; a bulb can get hot enough to ignite clothing, stacked blankets, or storage boxes.
Attached garage: There must be at least one receptacle—not counting receptacles used for laundry or other utilities. There should be an overhead light (in addition to a light that is part of a garage door opener) controlled by at least one wall switch.
Kitchen: Many codes call for two 20-amp small appliance circuits controlling GFCI receptacles placed above countertops. Other codes call for 15-amp split-circuit receptacles. The refrigerator, microwave, garbage disposer, and dishwasher may need to be on separate circuits. The lights should be on a separate 15-amp circuit.
Bathroom: Codes require that all receptacles be GFCI-protected. Any light fixture should have a sealed globe or lens to shut out moisture. A fan/light/heater may draw enough power to require its own circuit.
Outdoors: Standard-voltage wiring requires either waterproof underground feed (UF) cable or conduit or both. The depth at which the cable must be buried varies by local codes. Special waterproof fittings and covers are called for. For low-voltage lighting, standards are less strict; usually no permit is needed.
If the box is plastic, connect the ground wire to the receptacle only. For a middle-of-run receptacle (shown), splice the ground wires together and connect to the receptacle with a pigtail.
With a metal box, attach ground wires to both the receptacle and to the box using a grounding screw. Use a pigtail and a grounding wire nut.
Systems that use armored cable or metal conduit may have no grounding wire. The sheathing or conduit provides the path for ground, so it must be connected firmly at all points.