What is XHHW / XHHW-2 Wire?
XHHW is cross-linked polyethylene insulated 90°C building wire. XHHW-2 adds 90°C wet rating. Same NEC fill area as THHN.
XHHW is a building wire with cross-linked polyethylene (XLPE) insulation, rated for 90°C dry and (for XHHW-2) 90°C wet. It's an alternative to THHN/THWN-2 with better high-temperature ageing and UV resistance.
Construction
- Conductor: Solid or stranded copper or aluminum
- Insulation: Cross-linked polyethylene (XLPE), 30–55 mils depending on gauge
- Outer jacket: None — XLPE is the only insulation layer
- Voltage: 600V
- Temperature: 90°C dry (XHHW) or 90°C wet/dry (XHHW-2)
XHHW vs XHHW-2
- XHHW (original): 75°C wet / 90°C dry
- XHHW-2: 90°C wet AND dry (matches THHN's dry rating)
For wet locations and modern installations, specify XHHW-2.
Why cross-linked polyethylene?
XLPE has several advantages over PVC:
- Better long-term ageing at high temperature — important for industrial environments
- UV resistance — better for outdoor service life
- Chemical resistance — handles oil, mild acids, and many solvents better
- No nylon jacket needed — single-layer insulation is mechanically robust
The trade-off is cost (10–20% more than THHN) and slightly higher pulling friction (no nylon slip).
Common applications
- Solar PV array circuit wiring — UV exposure, decades of service. XHHW-2 dominates this market alongside USE-2.
- High-ambient industrial: Furnaces, smelters, areas where ambient temperature regularly exceeds 40°C.
- Underground service-entrance laterals: Cross-linked polyethylene handles moisture and soil chemistry well.
- Direct buried (when permitted with USE-2 dual stamp): XHHW-2/USE-2 dual-stamp is common.
Fill = same as THHN
NEC Table 5:
| Gauge | THHN / XHHW area |
|---|---|
| 14 AWG | 0.0097 |
| 12 AWG | 0.0133 |
| 10 AWG | 0.0211 |
| 8 AWG | 0.0366 |
| 6 AWG | 0.0507 |
| 4 AWG | 0.0824 |
| 4/0 | 0.3237 |
| 500 kcmil | 0.7073 |
The XHHW wire fill chart and the THHN wire fill chart show identical conductor counts.
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This page's figures are transcribed from NEC 2023 (NFPA 70) Chapter 9, Tables 1, 4 and 5, and checked by a version-controlled automated test suite — they are not signed off by a licensed professional. WireFillChart is an independent reference, not affiliated with or endorsed by NFPA. Always verify against the code edition adopted by your local authority having jurisdiction (AHJ).