How to Understand Different Household Wire Types

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In every home, there is an electric panel. In every electric panel, there are a number of circuit breakers. Connected to each of these circuit breakers are wires. Most homeowners may be surprised to discover that the wires need to be a certain gauge when connected to a certain breaker. You just cannot make your connections randomly. Electrical wire can be broken down into three subcategories: the wire type, the wire size and the wire color. Here is how to understand the different household wire types.

How to Know Wire Types

  • In most American homes there are typically four types of wires that are used. These include flexible metal-covered wire (BX), plastic sheathed nonmetallic (NM) cable (also commonly called electrical wire), lamp cord and low voltage wire.

  • Metal-covered wire, or BX, is not commonly found in homes, although it can be used in some cases. It is more common in industrial or commercial applications. However, it is found on recessed lights in the home where it delivers the wires from the mounted junction box to the socket. It has a spiraled metal sheath which allows the wire to remain somewhat flexible. Inside there are regular insulated wires (gauge and number of conductors as needed) which are contained in a paper wrapping.

  • Plastic sheathed wire (or NM cable) is another type of wire. Commonly called electrical wire, NM cable is what is most commonly found inside the home. It is extremely flexible which makes it ideal for interior applications. While most NM cable is sheathed in white plastic, other colors are available to help identify dedicated circuits. Just like BX, NM cable is available in a variety of gauges and conductors.

  • The next type of wire found in homes is lamp cord. Lamp cord is made up of two insulated lengths of stranded wire and is never to be used for fixed applications like wiring a light fixture or receptacle. It is very thin wire and should only be used for repairing lamps.

  • Low voltage wire is another popular wire found in American homes, as it is used to supply power to things such as doorbells, alarm systems, telephones and thermostats. This wire is extremely thin (usually 24-gauge) and can come in a wide range of application-ready designs.

How to Know Wire Sizes

  • The rule of thumb for wire gauge (size) is that the lower the gauge, the bigger the wire. Instead of listing the wire by diameter size, the American Wire Gauge (AWG) system expresses the size as a whole number. For instance, instead of listing a wire as 0.0064 inches in diameter, the wire is listed as No. 14 wire, or 14-gauge wire.

  • The smaller the gauge, the more power the wire can handle. For example, 12-gauge wire can deliver more power than 14-gauge wire. This is because the wire's diameter is larger and offers more room for the current to move. The National Electric Code (NEC) requires a minimum of 14-gauge wire to be used for most home wiring, but that is also dictated by breaker size.

  • Simply put, you cannot connect a 14-gauge wire to a 30-amp breaker. Sure, the circuit will work if you do, but, if there is a problem on the circuit the 14-gauge wire will heat up and melt before the 30-amp breaker will trip. This is a huge fire hazard. A 30-amp breaker needs to deliver electric through at least 10-gauge wire in order for the circuit to be properly protected.

  • The largest sized wire you will see in your home is the electric panel's feed wire which is usually connected to a 100-amp breaker. The feed size is No. 3 wire.

  • Here is a quick breakdown for which size wire should be connected to which sized circuit breaker:

    14 wire-15-amp breaker
    12 wire-20-amp breaker
    10 wire-30-amp breaker
    8 wire-40-amp breaker
    6 wire-60-amp breaker
    3 wire - 100-amp breaker

    Most of these wires are available in either solid-wire or stranded-wire types.

How to Know Wire Colors

  • In most home-wiring applications, the circuit features one black wire, one white wire and a green or non-insulated ground wire. On this type of circuit the black wire is delivering the voltage and the white is acting as the neutral. The circuit has to have each in order to be complete. In some cases a white wire may be used as a hot feed. When this occurs it is commonplace for the white wire to have a strip of black electrical tape around the insulation to signify that it is being used as a hot wire.

  • You may notice a red wire from time to time. The red wire has a couple of responsibilities: It can be a second circuit, sharing the neutral with the circuit fed by the black wire or it can be a traveler, as used in a three-way switch configuration. Additional conductors like the one found in 4-wire electrical wire may be colored blue.

  • While some 240-volt circuits use different colored wires including orange, yellow, brown and gray, they are not typically found in the residential home, so we will go into those applications in another article.

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