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Wires and cables

Use the right wire and cable to avoid creating a dangerous installation that you’ll have to tear out and redo. Here are the basics:

WIRES. Wire is usually made of a single, solid strand of metal encased in insulation. For flexibility and ease of pulling, some wire is stranded (above right). Wire is sized according to American Wire Gauge (AWG) categories. Size determines how much amperage the wire will carry, and as of 2002, the color of the outer jacket tells you what gauge the wire is. Common household wires and their ratings and colors are:

• #14 wire (also called 14-gauge) carries 15 amps and is white.

• #12 wire carries 20 amps and is yellow.

• #10 wire carries 30 amps and is orange.

• #8 wire carries 30 amps and is black (as are all the gauges with numbers less than 8).

A wire that is overloaded to carry more amperage than it is rated for will dangerously overheat. Older wires have rubber insulation, which deteriorates after about 30 years. New wires have longer-lasting polyvinyl insulation. Insulation color often tells the function of wire: Black, red, or other colors indicate hot wire. White or off-white wire generally is neutral. Green or bare wire is ground.

TYPES OF ELECTRICAL CABLE. Cable is two or more wires wrapped together and sheathed in plastic or metal. Nonmetallic (NM) cable is permitted inside wall, ceiling, and floor cavities. Special nailing plates must be added to the framing to protect the cable from puncture . Printing on NM cable tells you what is inside: 12/3 means there are three #12 wires plus a ground wire. “G” means that there is a ground wire. For underground installations and in damp areas use underground-feed (UF) cable. UF cable encases the wires in solid plastic. Telephone cable is being supplanted by CAT 5E cable, suitable for telephones, modems, and computer networking. Coaxial cable carries television signals. Armored cable has a flexible, metal sheathing. One type of armored cable is BX (also called AC), which has no ground wire—the sheathing is used for grounding (the thin metal bonding strip cannot be used as a ground wire). The other armored cable is metal-clad (MC) cable, which has an insulated green grounding wire. (A similar material, Greenfield, or flexible conduit, is armored sheathing without wires. Install it, then pull wires through it.) Conduit is a solid pipe through which individual wires are run. Metal conduit is often required in commercial installations. Most building departments require it only where the wiring is exposed (not behind plaster or drywall).

UPGRADE CABLE WHENEVER YOU CAN - Sometimes when you remodel, especially in an older home, it's a good idea to kill two birds with one stone. A couple I know was pulling down some plaster walls and found some working wires running through them. The wires seemed in pretty good shape and even had a ground, so they asked me about leaving them. I told them nothing lasts forever and as long as the stuff was exposed anyway, upgrade while the job was easy. That way you won't have to tear down new walls if the wire goes bad.

Wire nuts and tape

Wire nuts are required for all splices. The color of the wire nut indicates how many wires of a given size it can handle. Use yellow connectors for splices as small as two # 14s or as large as three #12s. Orange nuts handle combinations ranging from two #16 wires up to two #14s. Use green wire nuts for ground wires only. The hole in the top allows you to make an instant pigtail, with one wire poking out. Red wire nuts will grab splices as small as two #12s and as large as four #12s. Black or blue silicone wire nuts are waterproof once connected, though they should be protected by waterproof junction boxes.

SPLICING WIRES - A guy I know makes his splices without twisting the wires together before he twists on a wire nut. "Just as strong and saves time,” he said. "So, how much time will you save when one comes loose and you've got to take down an entire circuit to find the problem?" I asked. Believe me, you actually save time by doing the job right the first time.

Receptacles and switches

Most switches and receptacles in a home are designed to carry 15 amps. Look on the metal plate for the amperage rating. Any 15-amp device should be connected to #14 wire, which should lead to a 15-amp fuse or circuit breaker in the service panel. Be sure that the amperage of a 240-volt receptacle is rated no lower than that of the appliance. If you are unsure as to which receptacle to use, check with your building department or ask an electrician.

SINGLE-POLE. This switch has two terminals for hot wires and a green terminal for ground. It is the most common household switch.

THREE-WAY. Three-ways are installed in pairs—both switches control the same light(s) in either direction. There are no ON and OFF markings.

DESIGNER SWITCH. These have built-in night lights and large easy-to-find toggles. They are available in single-pole and three-way.

120-volt receptacles:

UNGROUNDED 120-GROUNDED 15-AMP, 120-VOLT. This is the most common household receptacle. It will overload if you plug in two items drawing more than 15 amps.

20-AMP, 120-VOLT. This receptacle has a neutral slot shaped like a sideways T so that you can plug in large appliances or heavy-use tools. It should connect to #12 wires that lead to a 20-amp circuit or fuse in the service panel.

240-volt receptacles:

WALL-MOUNTED 240-VOLT RECEPTACLE. Appliances using 240 volts have different plug designs to ensure that they are plugged into the correct receptacle. To be safe, check the information plate on the appliance to confirm that the amperage also matches that of the receptacle.

WALL-MOUNTED 120/240-VOLT RECEPTACLE. This receptacle is typically used with a stove. Install it in a standard electrical box.

SURFACE-MOUNTED 120/240-VOLT RECEPTACLE. Some heavy-duty appliances require receptacles with both standard voltage and high voltage. For example, a range commonly uses 240 volts for its burners and 120 volts for the light and the clock. A 120/240-volt receptacle provides both levels of power.

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