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THHN Wire

May 11, 2016 - Posted by admin

What is THHN wire?

thhn-wiresTHHN wire is one of the most popular types of electrical wires used in residential, commercial and industrial constructions. It has many benefits when compared to other types of wire.

What does THHN stand for?

As with most wiring, these abbreviations specify what material the outer insulation is made out of and some of it’s characteristics. In this case, THHN stands for thermoplastic high heat-resistant nylon. Thermoplastic is a PVC material, which is much thinner that most other types. This allows for thinner wires and easier pulling. The outer protection jacket is made of nylon, which also allows for easier pulling, since the nylon makes the wire slide more.

Where can THHN wire be used?

THHN wire is allowed for use in dry and damp locations only. If you require wiring for wet locations, you must use THWN wire. It’s important to note that now many wires in the market are dual rated both THHN and THWN, which means the wire can be used in dry, damp, or wet locations.

THHN wire is rated for high heat: it can be found with insulation rating as high as 90°C or 194°F.

What about THHN/THWN-2

As mentioned previously, most of the time you ask for THHN wire they’ll give you a wire rated as THHN/THWN, which means it has the characteristics of both THHN and THWN, namely it can be used in dry, damp, or wet locations. The limitation is that when used in dry or damp locations the insulation rating is 90°C, but if you are using it in a wet location you should use 75°C.

The THHN/THWN-2 wire doesn’t have this limitation. In other words you can use 90°C as your insulation temperature rating even in wet locations.

Precautions when using THHN wire

Thermoplastic, which is the material that a THHN wire’s outer jacket is made of, will release a toxic gas when burned. For this reason it is recommended to always be placed inside a conduit. Also, always consult the National Electrical Code or other relevant electrical code in your jurisdiction before doing electrical work.

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