Aluminum or Copper: 

The two common conductor materials used in residential and commercial solar installations are copper and aluminum. Copper has a greater conductivity than aluminum, thus it carries more current than aluminum at the same size.

Aluminum may be weakened during installation especially during bending, however it is less expensive than copper wires. It is not used (not permitted) for interior home wiring, as they are used in larger gauges for underground or overhead service entrances and for commercial operations.

Solid or Stranded: The cable could be solid or stranded, where stranded wires consist of many small wires that allow wire to be flexible. This type is recommended for larger sizes. The current tends to flow on the outside of the wire, thus stranded wires have slightly better conductivity as there is more wire surface.

Insulation: The insulation covering wire can protect the cable from heat, moisture, ultraviolet light or chemicals. 

  • THHN is commonly used in dry, indoor locations.
  • THW, THWN and TW can be used indoors or for wet outdoor applications in conduit.
  • UF and USE are good for moist or underground applications.
  • PV Wire, USE-2 and RHW-2 cables can be used in outdoor and wet conditions where their outer cabling is UV and moisture resistant. They must be sunlight resistant.


Color: Electrical wire insulation is color coded to designate its function and use. For troubleshooting and repair, understanding the coding is essential. The wiring label differs according to AC or DC current.