The initials, or acronym, for XHHW stand for Cross-Linked High Heat Water Resistant Insulated Wire. This XHHW is the designation for a specific insulating material for electrical building wire and cable. The term XHHW also designates the temperature rating as well as the conditions that the cable can be used under.
XHHW insulated wires are generally used in residential, commercial and industrial buildings and installations for the purpose of power distribution. The cable is manufactured in both copper and aluminum conductors and typically ran in conduit or other approved raceways for services, feeder and circuit wiring. XHHW insulation is rated by the Underwriters Laboratories (UL) to be suitable for use in dry locations up to 90 degrees Celsius, or wet locations up to 75 degrees Celsius. However, there is a newer and much more popular insulation version of XHHW with the designation of XHHW-2. This allows the insulation to be suitable for use in both wet and dry locations up to 90 degrees Celsius.
The operating voltage for XHHW is usually ranging but not exceeding 110-600 Volts. The conductors that are, and can be used with XHHW insulation are both copper and aluminum. The conductors can be either of a solid or stranded construction with the stranded being much more flexible. As you move up to the larger gauge sizes you will find that stranded becomes your only option due to the flexibility of the cable. It is good to note that XHHW ranges in size from 14 AWG (American Wiring Gauge) all the way to 1000 MCM (Thousand Circular Mils).
It is also worth noting that XHHW, due to its construction, is not only water resistant but also very resistant to chemicals, ozone and abrasions. This along with the wide range of sizes makes this an optimal choice for end users of all types.