Understanding Different Types of Wires and Cables
With our houses running on more electricity than ever, a basic understanding of the cables and wiring in your home is vital. Use this fact sheet to learn about a variety of different kinds of wires before you start your next electrical project.
Wire and Cables Safety Tips
When working with something as sensitive as electricity, safety should be your first and foremost concern. Here are some simple safety tips to keep in mind for avoiding common electrical mistakes.
Always follow manufacturer recommendations for outdoor use of cables and never use a household extension cord outdoors. Damaged or worn extension cords need to be replaced, never repaired. Also, you'll want to replace older cords that are non-polarized and don’t have safety closures because these do present a safety risk. On the reverse side, you never want to remove the third prong or cut down the blade of a plug to fit a non-polarized receptacle either.
Before you plug anything into an extension cord, you should always know the length of cord needed and the electrical load it can carry. Cord should reach easily from wall outlet to appliance without tension, and you should never put two short cords together to obtain needed length. Just go out and buy a new cord in the proper length.
Only use an extension cord that has been tested by a nationally recognized testing laboratory such as UL, CSA, or ITS. This should be denoted on your cord's label or molded into the end of the cord depending on how new it is. Cord should also be permanently bonded to the plug and the connector to ensure a good connection and no exposed wiring. Faulty cords shouldn't make it through inspection, but some might. If your cord isn't properly bonded, either throw it away or return it to the store for a new one.
Keep cords out of the reach of children and out of high-traffic areas where people might trip over them. Not only is this a safety hazard, but it could damage your cord or your socket if the cord is ripped out by someone's foot. Also, never cover cords with carpet, furniture, or appliances. If you have trouble keeping your cords out of the way and out from under things, considering rearranging your room instead.
Wire itself is different than cable. Cable actually refers to two or more wires or conductors grouped together in a jacket. Wire is grouped by gauge number, running from 0000 to No. 40. The smaller the number, the thicker the wire. For home use, the most common gauges are between 10 and 20. While larger wire carries more current, forcing too much current through a wire will cause it to overheat and trip a breaker. Larger wire is also just generally unnecessary for home use. The most common conductor in home wiring is copper or tinned copper because it has minimum resistance at reasonable cost. Wire is also characterized by letters that correspond to the insulation type and electrical capacity.
Grounding wire provides a path of least resistance from the frame or case of an appliance to the ground to guard against electric shocks. Both two- and three-conductor cables can carry grounding wires.
Like it was said above, cable refers to a collection of two or more strands of wire or conductors. Basically, cable has a “hot” line to carry the current and a “neutral” line to complete the loop. They also often have a third wire, that grounding wire.
Cables are classified according to the number of wires it contains and their size or gauge. All cables are marked with a series of letters followed by a number, a dash, and another number. The letters indicate the type of insulation (cord, wire, and insulation). The first number indicates the resistance of the wires in the cable, and the number following the dash indicates the number of individual conductors in the cable. If the designator “G” follows the series it means that the cable is also equipped with a non-current-carrying ground wire. So, for example, the designator USE 12-3/G indicates an underground cable containing three separately insulated wires capable of carrying 20 amps of current plus a grounding wire.
There are several specific types of cable that are commonly used. Two-conductor cable contains one black wire and one white wire. The black wire is always the “hot” wire and must be fused. The white is always neutral and must never be fused. When current bridges the gap from the 110V hot wire to the neutral, it results in a 110V input to the appliance.
Three-conductor cable contains a red wire in addition to black and white. The black and red wires are “hot,” carrying 110V each, and both must be fused, while the white still remains neutral. This three-wire circuit is increasingly common in home wiring; it accommodates major 220V appliances, such as ranges and air conditioners.
BX cable is armored, metallic cable. It consists of two or three insulated wires individually wrapped in spiral layers of paper. The steel casing acts as a ground wire. There is also a bond wire included in the casing that acts as a ground if the casing breaks.
Romex™ cable has a flat, beige thermoplastic jacket surrounding two or three wires. Each wire is wrapped in insulation and a spiral paper tape. Type NM means it can be used indoors. Type NMC means it can be used indoors or outdoors. Type UF means it is suitable for use underground outdoors.
The most common jackets for cable are NM-B (Non-Metallic Building Indoor), UF-B (Underground Feed), and BX, which is flexible metallic cable.
Now, let's look at a few more specific types of wiring and cable that you will see around a modern home.
Thermostat cable is used in low-voltage control, alarm, and communication systems. The most common types of this cable are braided, twisted, and plastic-jacketed types; however, all three use solid copper conductors and are twisted and insulated with plastic.
Twisted cable, which has no outer braid, is used in doorbells, burglar alarms, intercom telephones and public address systems, while braided cable is covered with cotton braid and is used primarily in thermostat controls and other low-voltage, remote control circuits. Plastic-jacketed cable is actually also used in low-voltage applications similar to braided cable.
Although thermostat cable is low voltage, it carries a UL-listing for being flame-retardant, since it is installed in the wall. Wiring used in security alarm and smoke detection systems must all be UL-listed.
TV Wire and Accessories
Television lead-in wire connects the receiving set to the antenna. Good quality 300-ohm wire is used for both VHF and UHF receivers. A TV set coupler is a loss-producing device for connecting two or more TV receivers to the same antenna. The loss introduced into the circuit is small, but can be critical in “fringe area” reception. In such areas, customers should be told of this small loss and to expect a slight reduction in signal strength at the receiver.
A lightning arrestor mounts on the outside of the house as close to the TV receiver as possible to protect the receiver against lightning damage. The lead-in wire is attached to proper contacts and the ground rod to ground connector. Lightning should jump the gap inside the arrestor and flow into the earth if the circuit is properly installed.
Home networks connect multiple computers in the home, satellite dishes, cable TV, and sophisticated audio systems. The heart of these systems is the networking hub. Usually thought of in conjunction with computers, the home network hub differs in that it provides central control of computers, peripherals, phones, TVs, and audio components. This is the unit where most of the wiring from different locations comes together to meet.
Most home networks use coaxial, Category 3, and Category 5 cable. Coaxial cable is used for TVs, VCRs, and satellite equipment. Category 3 cable is used for telephones while Category 5 is used for telephone, fax, and computer systems. Some cables will combine different functions into single cable.
“Structured” wiring refers to a bundle of cables that runs from the networking hub to meet a home’s future information-carrying needs. This wire bundle may consist of some combination of Category 5 cables, fiber-optic lines, Category 3 cables, and coaxial lines.
Jacks are used to terminate the cable. There are different jacks for telephones, computers, satellite, audio, and video equipment. Many of these jacks and cable connectors require special tools for installation.
Patch cords are used to connect different computer and audio/video devices with one another or with a central networking device such as a hub.
Binding posts are used to connect bare speaker wire, while F-Connectors are used with coaxial cable.
Indoor extension cords come in two-wire cords and in lengths from 6' to 15'. White and brown are the basic colors, with occasional outliers. Outdoor extension cords are used for outdoor power tools and exterior lighting, such as seasonal decorations. They come in 16/3, 14/3, and 12/3 wire, with the most common lengths ranging from 25' to 100'. Heavy-duty extension cords should be used with high-wattage appliances. These are commonly orange in appearance.
Any UL-listed cord will carry a UL label near the female end. Many companies are now using an alternative method of labeling allowed by UL, which permits the UL markings to be molded into the cord ends. This ensures a permanent marking that cannot be provided with a label. It is important to check for this UL insignia, whether it is a label or a permanent marking. Non-listed cords can be similar in appearance to listed ones.
To be UL-listed for outdoor use, three-wire round cords must have connector and cap molded to the cord and a lip on the end of the connector to prevent misuse. Beginning in 1998, UL-listed outdoor cords began appearing with the “SJTW” marking on the cord, not “SJTW-A” as was previously used. For a period of time, either marking will be acceptable for outdoor use.
Grounding cords are available in both heavyweight and heavy-duty construction, differing from standard cords because they have three conductors instead of two and are equipped with a three-prong grounding plug and connector.
Step-saver cords have built-in pendant switches to control appliances and lamps across the room, and wind-up reels keep tangled, foot-catching cords off the floor for ease of use.
Appliance cords combine the cord and connector. The difference between cord sets can be in type of connector and/or cord used. There are also free-end attachment cord sets without connectors used in re-wiring direct attachment irons, toasters, and similar small appliances. They have pre-tinned ends to speed up wiring.
Range and Dryer Cords
Range and dryer cords are free-end types, commonly called “pigtails,” attached directly to the appliance. Free ends are fitted with cable terminals that connect to screw terminals of the appliance to assure positive connections. A metal clamp attached to the cable serves as a strain relief at the point where the cable enters an appliance and a cord protector.
Heavy-duty attachment plugs for ranges and dryers are much larger than standard attachment plugs. Most are “L” shaped with a power cord feeding out the side of the plug. Sizes range from 30 to 50 amps for various models of dryers and ranges. The different amperage attachment plugs are not interchangeable because of a difference in their configuration.
A recent change in the National Electrical Code requires new range and dryer receptacle installations to be 3-pole, 4-wire grounding receptacles. The neutral (grounded circuit conductor) can no longer be used to ground the frames of electrical ranges and dryers.