Types of Residential Electrical Wire
- Nonmetallic (NM) sheathed cable wiring is most commonly used for indoor wiring projects and in rooms that are dry, such as kitchens and room additions as opposed to bathrooms and laundry rooms, which are high-humidity environments. Although this type of wire is referred to collectively as a cable, it actually consists of a number of wires bound together by an exterior sheath. NM sheathed cable is often sold in lengths ranging from 25 to 250 feet. The cable is spooled within a box for its convenient removal. NM cable is produced in a number of gauges and can be used for two-wire with a ground wire purposes or for three-wire with a ground wire applications.
- As its name suggests, large-appliance cable is specifically designed to accommodate the higher amperage required by large appliances, such as kitchen ranges and other appliances that require 40 or 50 amps. Because this type of wire is designed to handle significant electrical loads, it is generally available only in gauge six or gauge eight. Like NM sheathed cable, large-appliance cable also consists of several wires bundled together within an exterior wrap. Large-appliance cable's wires are made of brass, however, to enable easier bending than other wire materials provide. Large-appliance cable can accommodate two-wire and three-wire applications.
- Underground feeder (UF) wire is designed for rooms subject to dampness and/or high humidity, such as bathrooms and laundry rooms. For this reason, UF wire is commonly used where the installation of NM sheathed cable is not appropriate. It also can be used for outdoor circuits because it is weather-resistant. UF wire can be identified easily by its gray or white sold-core vinyl sheathing. Although this wire type can be routed underground, certain areas' building codes may prohibit its use in that manner.
- Whereas the names of other wire types are associated with a particular wiring job, the "THHN/THWN" part of THHN/THWN wire's name refers to wire rating. THHN/THWN wire is most commonly routed through conduit, making it very versatile. Unlike the other wire types, which feature several wires wrapped within a sheath, THHN/THWN wires are individual wires that must be purchased individually. THHN/THWN wire is more resistant to heat than unrated wiring. The rated wire is identified by the "THHN/THWN" stamp along its insulation.