300 MCM XHHW-2 copper building wire is one of several different types of copper wire that is primarily used in buildings. Its uses are set down in the National Electrical Code 1 guidelines, which also include how the wiring should be constructed. As an XHHW wire (which is shorthand for Cross-Linked High Heat Water Resistant), this type of wiring is highly insulated. Because it’s made out of copper, the 300 MCM XHHW wiring has a number of advantages over similar wire made from aluminum, including the fact that it can conduct electricity even after coming into contact with air.

The wiring meets or exceeds all of the following:

  • ICEA 2-95-658 / NEMA WC70
  • Federal Specification A-A-59544
  • NEC
  • UL Standard 44
  • c(UL) Type RW90
  • OSHA requirements for use.


This type of wiring is made from soft annealed copper wire. The copper used meets ASTM B8. It has an AWG of 300 and is made up of 37 strands. The wire’s insulation, which is made from cross-linked polyethylene, has a thickness of 65 mils. The nominal O.D. of this wire is 744. It’s fairly heavy, weighing upwards of 995 pounds per every 1,000 feet.

The ampacity of 300 MCM XHHW-2 wiring is 240 amps when operating at 60 degrees Celsius. The wire is rated for 285 amps at 75 degrees Celsius and 320 amps at 90 degrees Celsius.


300 MCM XHHW-2 wiring is designed primarily for use in buildings, both residential and commercial. It may also be found in some industrial sites. The wiring can be used in raceways and in conduits. It may be used for feeders, services, or branch circuits as outlined in the guidelines of the National Electrical Code.

This wiring is very versatile for two different reasons. First, it’s flame resistant. The cross-linked polyethylene will prevent most fires from spreading outside of the copper wire because it’s flame proof. Fires will eventually use up all of the oxygen available within the tubing, putting themselves out. While this will then necessitate replacing sections (or perhaps all) of the wiring, it will prevent the building from catching on fire. This wiring does add an extra layer of safety to businesses and homes because it can prevent damage from an electrical fire.

The other reason this wiring is often used in buildings is because it’s waterproof. It can be used in basements and other areas that are damp or where the wiring may actually sit in standing water for long periods of time. Because of that, this wiring is ideal for locations that contain both dry and wet areas or may be flooded.

Because it’s also very resistant to pressure and compression, the wire can be used in areas that will be filled with cement.

The maximum temperature the 300 MCM XHHW-2 wiring is rated for is 90 degrees Celsius. Any higher than that can lead to erratic behavior or even a complete loss of conductivity. This wire is also rated for use of no more than 600 volts.

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