XHHW-2 Wire: Ratings, Ampacity and XHHW vs. THHN
XHHW-2 is a single-conductor building wire with cross-linked polyethylene (XLPE) insulation, rated 90°C in both wet and dry locations. The letters stand for X (cross-linked polymer insulation), HH (high heat, 90°C), W (wet locations) and -2 (the 90°C rating also applies when wet). It's sold in copper and aluminum and is the usual conductor for aluminum feeders and services. For sizing, it uses the same NEC Table 310.16 columns as THHN/THWN-2.
XHHW, XHHW-2 and XHH ratings
| Type | Insulation | Dry and damp | Wet | Typical use |
|---|---|---|---|---|
| XHHW-2 | Thermoset XLPE, no jacket | 90°C | 90°C | Feeders, services, wet and underground raceways |
| XHHW | Thermoset XLPE, no jacket | 90°C | 75°C | Older or general stock; limited to 75°C when wet |
| XHH | Thermoset XLPE, no jacket | 90°C | Not permitted | Dry and damp locations only |
| THHN | Thermoplastic PVC with nylon jacket | 90°C | Not permitted | Dry and damp branch circuits |
| THWN-2 | Thermoplastic PVC with nylon jacket | 90°C | 90°C | Most THHN is dual-rated THHN/THWN-2 |
Temperature ratings from NEC Table 310.4(1) (2023). The marking on the conductor decides what it's listed for: many products carry several types, such as XHHW-2/XHHW/USE-2 or THHN/THWN-2.
The "-2" matters in wet locations, which include underground conduit and outdoor raceways (conduit in a wet location is itself a wet location). Plain XHHW drops to its 75°C rating when wet; XHHW-2 keeps 90°C.
XHHW-2 ampacity chart (NEC Table 310.16)
XHHW-2 is a 90°C conductor, so it appears in the 90°C column. Most circuits are limited to the 75°C column by their terminations, so both are shown:
| Size | Copper 75°C | Copper 90°C | Aluminum 75°C | Aluminum 90°C |
|---|---|---|---|---|
| 14 AWG | 20 | 25 | — | — |
| 12 AWG | 25 | 30 | 20 | 25 |
| 10 AWG | 35 | 40 | 30 | 35 |
| 8 AWG | 50 | 55 | 40 | 45 |
| 6 AWG | 65 | 75 | 50 | 55 |
| 4 AWG | 85 | 95 | 65 | 75 |
| 3 AWG | 100 | 115 | 75 | 85 |
| 2 AWG | 115 | 130 | 90 | 100 |
| 1 AWG | 130 | 145 | 100 | 115 |
| 1/0 AWG | 150 | 170 | 120 | 135 |
| 2/0 AWG | 175 | 195 | 135 | 150 |
| 3/0 AWG | 200 | 225 | 155 | 175 |
| 4/0 AWG | 230 | 260 | 180 | 205 |
| 250 kcmil | 255 | 290 | 205 | 230 |
| 300 kcmil | 285 | 320 | 230 | 260 |
| 350 kcmil | 310 | 350 | 250 | 280 |
| 400 kcmil | 335 | 380 | 270 | 305 |
| 500 kcmil | 380 | 430 | 310 | 350 |
Allowable ampacities from NEC Table 310.16 (2023): no more than three current-carrying conductors in a raceway or cable, 30°C (86°F) ambient. 240.4(D) limits overcurrent protection to 15 A for 14 AWG, 20 A for 12 AWG and 30 A for 10 AWG copper (15 A for 12 AWG and 25 A for 10 AWG aluminum). The full table with the 60°C column is on the ampacity chart.
Which column you can use. The 90°C rating doesn't mean a 90°C ampacity. Under 110.14(C), the terminations decide: for circuits of 100 A or less (or 14 through 1 AWG) use 60°C unless every termination is listed for 75°C, and above 100 A use 75°C. The 90°C column is the starting point for derating.
Why the 90°C rating still matters: derating
When you apply correction or adjustment factors, you may start from the 90°C ampacity, as long as the result doesn't exceed the ampacity at the termination temperature.
Example: six current-carrying 4 AWG copper XHHW-2 in one conduit. The 90°C ampacity is 95 A. Four to six current-carrying conductors take an 80% adjustment (Table 310.15(C)(1)): 95 × 0.80 = 76 A. The 75°C limit for 4 AWG copper is 85 A, so 76 A governs. With a 75°C-only conductor you'd have started from 85 A and ended at 68 A.
The same applies to ambient correction under Table 310.15(B)(1), for example on a hot roof. A 90°C wet rating is what lets you take that credit in a wet or underground raceway, and that is the practical case for XHHW-2 over plain XHHW.
XHHW-2 vs. THHN/THWN-2
| XHHW-2 | THHN/THWN-2 | |
|---|---|---|
| Insulation | Thermoset (cross-linked); doesn't soften with heat | Thermoplastic PVC with a nylon jacket |
| Temperature rating | 90°C wet and dry | 90°C dry (THHN) and wet (THWN-2) |
| Ampacity (Table 310.16) | Same columns | Same columns |
| Diameter, small sizes | Thicker insulation, so fewer fit in a conduit | Thinner, so more fit |
| Pulling | Stiffer in small sizes; no nylon jacket | Nylon jacket pulls easily |
| Common use | Aluminum feeders and services, wet and underground runs | Copper branch circuits and feeders in dry or wet raceways |
Ampacity is the same. A 6 AWG copper conductor has the same Table 310.16 ampacity whether it's XHHW-2 or THHN/THWN-2. The choice is about the environment, the pull and the price, not the amps.
Conduit fill differs. Conductor areas in NEC Chapter 9 Table 5 depend on the insulation type, and XHHW is larger than THHN in the smaller sizes, so fewer conductors fit. Our conduit fill chart and calculator use THHN/THWN-2 areas; for XHHW-2, use the XHHW row of Table 5.
Where you'll see XHHW-2
- Aluminum feeders and services. Most aluminum building wire is sold as XHHW-2. A 200 A dwelling service on Table 310.12 needs 4/0 aluminum (200 A service wire size); a 100 A subpanel feeder at 75°C needs 1 AWG aluminum (100 A subpanel).
- Underground in conduit and outdoor raceways, where the wet rating matters.
- Industrial and commercial feeders, where the thermoset insulation's heat and abrasion resistance is preferred.
Check the conductor's marking for anything beyond the basic type: sunlight resistance, direct burial (USE-2) or a cable-tray rating are separate listings, not part of "XHHW-2" itself.
Frequently asked questions
What does XHHW-2 stand for?
X for cross-linked polymer (thermoset) insulation, HH for high heat (90°C), W for wet locations, and -2 for a 90°C rating that also applies in wet locations.
What is the difference between XHHW and XHHW-2?
Both are rated 90°C in dry and damp locations. In wet locations XHHW is limited to 75°C and XHHW-2 keeps its 90°C rating (NEC Table 310.4(1)).
Is XHHW-2 better than THHN?
Neither is better in general; they have the same ampacity. XHHW-2 has tougher thermoset insulation and a 90°C wet rating without a jacket, and it's the common choice for aluminum feeders. THHN/THWN-2 is thinner, so more conductors fit in a conduit, and it pulls easily.
What is the ampacity of 4/0 aluminum XHHW-2?
180 A in the 75°C column and 205 A in the 90°C column of NEC Table 310.16. Most terminations limit it to 180 A.
Can XHHW-2 be used underground?
In a raceway, yes: underground raceways are wet locations, and XHHW-2 is rated for them. Direct burial without a raceway requires a conductor or cable listed for it, such as USE-2; many XHHW-2 products are dual-marked XHHW-2/USE-2, so check the marking.
Can you use XHHW-2 in a house?
Yes, as individual conductors in a raceway, typically for a service or a feeder to a subpanel. Inside walls, most branch circuits use NM-B cable instead.
Values from NEC 2023 Tables 310.4(1), 310.16 and 310.12. Last updated: October 6, 2026. This page is a reference; the NEC edition adopted by your jurisdiction governs, and the conductor's marking decides its listing. Electrical work should be done by qualified people.
Sources
- NFPA 70, National Electrical Code, 2023 edition (NFPA offers free read-only access). Values on this page follow the NEC 2023; check the edition and local amendments your jurisdiction has adopted.
- Tables cited: Table 310.4(1), Table 310.12, Table 310.15(B)(1), Table 310.15(C)(1), Table 310.16 and Chapter 9, Table 5.
- Sections cited: 110.14(C) and 240.4(D).
- How the numbers are checked: how we build our calculators.