XHHW is Cross-linked High Heat-resistant Water-resistant wire: a single 600 V conductor insulated with cross-linked polyethylene (XLPE) instead of PVC, and with no nylon jacket. XHHW-2 adds a 90°C rating in wet locations as well as dry. It is the standard choice for large feeders, service entrances, and aluminum conductors above 1/0.
| Property | Value |
|---|---|
| Voltage rating | 600 V |
| Temperature rating (dry) | 90°C |
| Temperature rating (wet) | 75°C for XHHW, 90°C for XHHW-2 |
| Insulation | Cross-linked polyethylene (XLPE), no nylon jacket |
| Conductor | Copper or aluminum, stranded |
| Sizes | 14 AWG through 2000 kcmil |
| NEC article | Article 310, Table 310.4(A) |
| Direct burial | Not permitted as a bare conductor — requires a raceway |
| Flame rating | Passes the vertical flame test; permitted inside buildings |
| Typical use | Feeders, services, large aluminum runs, solar combiner wiring |
| Size | Ampacity |
|---|---|
| 14 AWG | 20 A |
| 12 AWG | 25 A |
| 10 AWG | 35 A |
| 8 AWG | 50 A |
| 6 AWG | 65 A |
| 4 AWG | 85 A |
| 3 AWG | 100 A |
| 2 AWG | 115 A |
| 1 AWG | 130 A |
| 1/0 AWG | 150 A |
| 2/0 AWG | 175 A |
| 3/0 AWG | 200 A |
| 4/0 AWG | 230 A |
Both are 600 V, both are 90°C in the -2 versions, and both need a raceway. The difference is the insulation chemistry, and it shows up in three places.
Size. XHHW has no nylon jacket but thicker primary insulation in small sizes, so 14 through 10 AWG XHHW is physically larger than THHN — 12 AWG XHHW is 0.0181 in² against 0.0133 in² for THHN, so fewer fit in a conduit. From 4 AWG upward the relationship reverses and XHHW is slightly smaller. See the conduit fill charts, which list both.
Pulling. The nylon jacket on THHN is slippery, which makes long conduit pulls easier in small sizes. XLPE has a higher coefficient of friction but is much tougher and far more resistant to cracking at low temperature, which is why it wins on large, heavy feeder pulls.
Heat and moisture. XLPE is thermoset rather than thermoplastic: it does not soften and deform when hot the way PVC does. That makes XHHW-2 the better conductor for sustained high-temperature service and for wet locations over long service lives.
Service entrance and feeder conductors above about 1/0, where the toughness of XLPE matters on a heavy pull and the slightly smaller diameter helps with conduit fill and lug fit.
Aluminum conductors generally. Most aluminum building wire above 1/0 — including the conductors inside SER and SEU cable — is XHHW-2 insulated.
Photovoltaic and battery systems, switchgear, and industrial installations where the ambient runs hot and the wet-rated 90°C figure is genuinely used for derating rather than as a formality.
XHHW and XHHW-2 are used for service entrance conductors, feeders, sub-panel supplies, and large aluminum runs pulled through conduit. XLPE insulation is tougher and more heat stable than the PVC used on THHN, which suits heavy pulls and hot environments.
The -2 suffix means 90°C in wet locations as well as dry. Plain XHHW is 90°C dry but only 75°C wet. XHHW-2 is what is normally stocked and is required for any underground or wet location run where you want the 90°C derating basis.
For large feeders and services, generally yes — XLPE insulation is tougher, more heat stable, and slightly smaller in sizes 4 AWG and up. For small conduit runs THHN is easier to pull thanks to its nylon jacket and takes less conduit space below 4 AWG.
No. Like THHN, XHHW is a single conductor that must be installed in a raceway. XHHW-2 is rated for the wet conditions inside a buried conduit, but direct burial without a raceway requires USE-2 or UF-B.