Understanding Different Types of Wires and Cables

by DoItYourself Staff

Wire & Cables Safety Tips

Advise customers to follow manufacturer recommendations for outdoor use and to not use a household extension cord outdoors.

Damaged or worn extension cords should be replaced, not repaired. Replace older cords that are non-polarized and don’t have safety closures.

Know the length of extension cord needed and electrical load it can carry. Cord should reach easily from wall outlet to appliance. Never put two short cords together to obtain needed length.

Only use an extension cord that has been tested by a nationally recognized testing laboratory such as UL, CSA or ITS.

Keep cords out of the reach of children and out of high-traffic areas where people might trip over them.

Never remove the third prong or cut down the blade of a plug to fit a non-polarized receptacle.

Do not cover cords with carpet, furniture or appliances.

Cord should be permanently bonded to the plug and the connector to ensure a good connection and no exposed wiring.

Wire

Different than cable. Cable refers to two or more wires or conductors grouped together in a jacket.

Copper or tinned copper is the most common conductor in home wiring because it has minimum resistance at reasonable cost.

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.

Larger wire carries more current. Forcing too much current through a wire will cause it to overheat and trip a breaker.

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.

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 often have a third wire as that acts as a grounding wire.

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. Hence, 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.

The most common jackets are NM-B (Non-Metallic Building Indoor), UF-B (Underground Feed) and BX, which is flexible metallic cable.

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. The white 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 is 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.

Thermostat Cable

Used in low-voltage control, alarm and communication systems. Most common types are braided, twisted and plastic-jacketed types. All three use solid copper conductors and are twisted and insulated with plastic.

Although thermostat cable is low voltage, it carries an UL-listing for being flame-retardant, since it is installed in the wall. Wiring used in security alarm and smoke detection systems must be UL-listed.

Twisted cable, which has no outer braid, is used in doorbells, burglar alarms, intercom telephones and public address systems.

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 also used in similar low-voltage applications.

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 will jump the gap inside the arrestor and flow into the earth if the circuit is properly installed.

Home Networking

Home networks connect multiple computers in the home, satellite dishes, cable TV, sophisticated audio systems and home.

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 combine different functions into one 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.

Extension Cord

Indoor extension cords come in two-wire cords in lengths from 6' to 15'. White and brown are the basic colors.

Outdoor extension cords are used for outdoor power tools and exterior lighting. They come in 16/3, 14/3 and 12/3 wire, and the most common lengths are from 25' to 100'. Heavy-duty extension cords should be used with high-wattage appliances.

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.

Wind-up reels keep tangled, foot-catching cords off the floor.

Appliance Cords

Combine cord and connector. The difference between cord sets can be in type of connector and/or cord used.

Free-end attachment cord sets without connectors are 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 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.