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THHN, THWN and THW Acronym Explanations

Years ago, you could buy THHN, THWN, THW, THHW or THWN-2 wires, each one made for a specific installation, but now we use multi-rated THHN/THWN-2 as a universal building wire.

THHN, THWN and THW are all types of single-conductor electrical wire used in homes and buildings to deliver power. Previously, each acronym was a completely different wire with different approvals. Each type was specific to an application and cost as such. THHN wire prices, for instance, were higher than those for non-nylon wires. However, nowadays, there is a universal THHN-2 wire that covers all approvals from all variations of THHN, THWN and THW.

What Is THWN Wire?

THWN is similar to THHN, except it is water-resistant, adding the “W” into the acronym. THWN is rated for up to 167°F or 75°C in wet environments, but its successor, THWN-2, is rated for 90°C in both wet and dry environments. Historically, THHN and THWN were separate wires, but now you’ll typically find their capabilities combined in the THHN/THWN-2 design.

THHN wire without a dual approval of THWN is not water-resistant. The water-resistance allowed it to be installed outdoors and in conduit when THHN wire could not. However, remember that they’re all combined into a universal wire now. If you buy THHN wire on our website, it will have all of the attributes of each acronym discussed on this page.

What Is THW Wire?

This one stands for thermoplastic, heat- and water-resistant wire. This acronym is missing the “N” for nylon-coated. The nylon coating looks like a little piece of plastic over a shoelace and protects the wire in a similar fashion. Without the nylon coating, the wire will be slightly cheaper and provide less environmental protection to THW wire. It’s actually difficult to find THW wire without the additional approvals of THHN and THWN because they were all combined into one.

You can probably imagine how difficult it was to design, manufacture, stock and price each of the separate types of electrical wire. That’s why they were combined into a universal THHN-2 wire at a very attractive price.