What is the Difference Between THHN Wire and THWN Wire

Water resistance of the THWN is the major difference. THHN is used for dry to damp applications with maximum temperatures of 90AC/194AF while THWN can be used in both wet and dry conditions with a maximum temperature of 75AC/167AF.

THHN building wire uses a thinner PVC insulation than THWN which may lead to current leakage in the event of chemical or environmental exposure. This PVC insulation also releases toxic smoke when burnt.

Due to its nylon coating, THHN is not flexible like the THWN. This leads to a lot of time and energy wastage during installation making THWN more preferable.

Because of the slight difference between the THHN wire and THWN wire, most THHN wires have a dual rating marked THHN/THWN on the cable and hence water resistant for use in both wet and dry conditions. The THHN/THWN has a maximum rating of 90AC/194AF in dry applications and 75AC/167AF in wet applications while transmitting 600 volts for both. It is the most standard electrical wire on the market because of its use in electrical cables as well as single conductor electrical wires.

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