The information printed on the sides of wire indicates its THHN/THWN, material, max voltage rating and gauge.
THHN/THWN letters represent the most common types of individual wires used in residential applications.
- T – Thermoplastic insulation
- H – Heat resistance
- HH – High heat resistance up to 194 degrees Fahrenheit
- W – Rated for wet locations
- N – Nylon-coated to resist damage from oil or gasoline
Material: Most wire will be marked “CU” for copper, the most common conductor of residential electricity. Because electricity travels on the outside of copper wire, wires are insulated to protect against fire and shock. Older wire could be aluminum or copper-clad aluminum.
Maximum voltage rating: This will be a number such as 600, which indicates the maximum voltage the wire can carry. It is recommended for safety purposes that you stay around 80 percent of the max wattage your gauge is capable of carrying.
Gauge: This indicates wire size, as defined by the American Wire (AWG) system. The most common gauges are 10, 12 or 14. Larger numbers represent smaller sizes or gauges of wire.
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