THHN vs XHHW-2: which building wire to pull
Published Sep 30, 2026
THHN and XHHW-2 are the two single conductors you will pull through conduit most often. Both are rated 600 volts, both come in copper and aluminum, and on most jobs either one will pass inspection. The differences show up in wet locations, underground runs, rough pulls and price.
What the letters mean
The names come from the insulation codes in NEC Table 310.4(1) (Table 310.104(A) in the 2017 edition and earlier).
- T: thermoplastic insulation (PVC).
- HH: rated 90 °C in dry locations. A single H means 75 °C.
- W: rated for wet locations.
- N: a nylon outer jacket over the PVC.
- X: cross-linked polymer insulation (XLPE), which does not soften when it gets hot.
- -2: rated 90 °C in wet locations as well as dry.
So THHN is PVC with a nylon jacket, 90 °C dry. Almost all THHN sold today is dual rated THHN/THWN-2, which adds a 90 °C wet rating. XHHW-2 is one layer of cross-linked polyethylene, 90 °C wet or dry.
Side by side
| THHN/THWN-2 | XHHW-2 | |
|---|---|---|
| Insulation | PVC with a nylon jacket | Cross-linked polyethylene, no jacket |
| Dry locations | 90 °C | 90 °C |
| Wet locations | 90 °C (THWN-2 rating) | 90 °C |
| Outside diameter | Smaller | A little larger in most sizes |
| Pulling | Slick nylon, good in long runs | Tougher insulation, resists nicks and abrasion |
| Colors | Full color range in small sizes | Usually black; color with tape on larger sizes |
| Price | Usually the lower cost | Usually costs more per foot in copper |
Where each one fits
THHN/THWN-2 is the default for branch circuits in EMT or PVC inside a building. The thin insulation lets more conductors fit in a raceway, which matters when you are filling a 3/4 in. conduit with 12 AWG. The color range makes circuit identification easy, and the nylon jacket slides well on long pulls.
XHHW-2 is the better choice where the conductor will sit in water or take abuse. Underground conduit is a wet location under the NEC, and conduit below grade often holds water for years. Nylon jackets can absorb moisture over time, while XLPE shrugs it off. XHHW-2 also handles abrasion and heat better, so it is common on service entrance and feeder runs, in industrial plants and in pulls with many bends.
Most aluminum building wire sold for services and feeders is XHHW-2.
Ampacity is the same for both
Because both are 90 °C conductors, NEC Table 310.16 gives them the same ampacity for the same size and metal. In practice you size from the 75 °C column anyway, because most breakers and lugs are rated 75 °C (NEC 110.14(C)). The 90 °C rating is still useful: you can start from the 90 °C column when you apply correction for high ambient temperature or adjustment for more than three current-carrying conductors in a raceway, as long as the final result does not exceed the 75 °C value at the terminals.
Choosing between them
- Inside a dry building, in conduit, on branch circuits: THHN/THWN-2.
- Underground conduit, rooftops, wash-down areas and anywhere the raceway can fill with water: XHHW-2.
- Long or rough pulls in larger sizes: XHHW-2.
- Aluminum service and feeder conductors: XHHW-2 is the common choice.
- Tight conduit fill with many conductors: THHN/THWN-2, because of its smaller diameter. Check fill with NEC Chapter 9, Tables 4 and 5.
Neither one is rated for direct burial. For that you need a cable or conductor marked for it, such as USE-2, UF-B or URD.
Shop the wire
- 12 AWG THHN/THWN-2 copper, 10 AWG and 8 AWG
- 6 AWG XHHW-2 copper and 2/0 XHHW-2 copper
- 4/0 XHHW-2 aluminum for feeders
- Everything else in copper building wire and aluminum building wire
Code rules change between NEC editions and local amendments. Check the edition your jurisdiction has adopted and ask your inspector when in doubt.