There are various different types of sheathed nonmetallic coated cables for use in electrical wiring for different applications. For example, indoor electrical wiring is normally done using NM sheathed cable, which stands for Non Metallic. Outdoor applications require a different type of sheathed cable, known as UF cable, because of its ability to resist breaking down from exposure to ultra violet light and other outdoor and environmental factors. There are a number of different types of UF cable that can be used, and a number of different specifications related to the UF cable that is produced for electrical wiring purposes.
Regular UF Cable
Regular type UF cable is available in a variety of different wire thicknesses and gauges, and is also available in a number of different wiring configurations. In contrast to type NM wiring, which is generally off white in color with regards to the sheathing, type UF cable is generally gray or black with regards to the sheathing of the cable. This makes it visibly different from type NM cable and that way it is less likely to be installed incorrectly or in applications where it should not be installed.
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UF B Cable for Underground Burial
For applications where the cable needs to be run underground without conduit, there is a type of UF cable that is made specifically for this purpose. Type UF B cable is made for direct burial underground without the use of conduit or other piping, and is also gray in color and is marked as type UF B cable to denote the difference between it and the regular type UF cable, which is not suitable for direct burial outside of conduit or the proper piping material. Type UF B cable is typically more expensive due to the different materials required to make the sheathing UV, moisture and temperature and corrosion resistant for underground applications.
Wire Gauge and Count
Both type UF and type UF B cables are available in different common wire sizes, also known as gauges, and common wire counts. For example, a 12-gauge wire with a hot and a neutral (black and white) wire and a ground would be considered a 12-2 UF wire cable. A three wire cable such as is used with dryers and higher amperage circuits would be a 12-3 UF cable. In each case, the ground wire is not counted as one of the wires, so there is always one more wire than is noted in the designation.
The maximum voltage of all types of UF wire including UF and UF B are all the same. The maximum voltage set for each of these types of wiring is set at no more than 600 volts.