“`html
THHN suits general-purpose building wiring in conduit for 600-volt circuits and is rated for dry locations unless also marked THWN-2.
For the full breakdown, see our best 10 AWG THHN Wire guide.
The difference between a THHN job that passes inspection and one that gets red-tagged is often a single letter printed on the jacket: W. Before you plan any conduit run, you need to know what THHN wire is suitable for — the restrictions matter just as much as the uses. This guide covers the code-accepted uses, the places THHN is not allowed, and the ratings that decide how much current it can carry.
What Can THHN Wire Be Used For?
THHN is a general-purpose building wire made for installation inside conduit and raceways, rated for circuits up to 600 volts. It’s the standard choice for new construction, rewiring, and branch circuits in commercial and industrial buildings under the National Electrical Code (NFPA 70).
The nylon jacket does the work: it eases pulling through conduit and protects the PVC underneath.
Approved uses include:
- Branch circuits in conduit or raceways in commercial and industrial settings
- New construction and rewiring projects at 600 volts or less
- Dry locations up to 90°C for wire marked only THHN
- Wet or damp locations when the jacket also reads THWN or THWN-2
Where THHN Wire Should Not Be Used
THHN marked only as THHN is not rated for wet locations, direct burial, open-air runs without a raceway, or use as a substitute for NM-B cable inside wall cavities. The printed marking on the jacket decides all of this, so read it before you buy. The nylon jacket is tough enough for pulling through conduit, but it is not rated for burial, and it does not replace the outer sheath of NM-B cable inside wall cavities.
| Application | Suitable? | Requirement |
|---|---|---|
| Branch circuits in conduit | Yes | Installed in conduit or raceway per the NEC |
| New construction / rewiring | Yes | 600-volt applications, general purpose |
| Commercial / industrial buildings | Yes | Primary NEC-listed application |
Dry locations
 Send us your feedback Tell us what you thought about this post — we read every note. |