XHHW Conduit Fill Guide
Cross-linked High Heat-resistant Water-resistant (XHHW) conductors are rated for 90 degrees C (194 degrees F) in dry locations, 75 degrees C (167 degrees F) in wet locations. This page provides complete conduit fill data for XHHW conductors in all standard conduit types and sizes per the National Electrical Code. Use the tables below to find the minimum conduit size for your installation, or visit the calculator for custom fill calculations.
XHHW Conductor Specifications
XHHW Conductor Areas (NEC Table 5)
The cross-sectional areas below include the conductor insulation and are used for all conduit fill calculations. These values come from NEC Chapter 9, Table 5. The area determines how many conductors of each size can fit in a given conduit per the NEC fill percentage rules (53% for 1 conductor, 31% for 2, and 40% for 3 or more).
| Wire Size | Area (sq.in.) | Typical Use |
|---|---|---|
| 14 AWG | 0.0139 | 15A branch circuits, lighting |
| 12 AWG | 0.0181 | 20A branch circuits, receptacles |
| 10 AWG | 0.0243 | 30A circuits, dryers, water heaters |
| 8 AWG | 0.0437 | 40-50A circuits, ranges, large equipment |
| 6 AWG | 0.0590 | 55-65A circuits, subpanels, large motors |
| 4 AWG | 0.0814 | 70-85A feeders, subpanels |
| 3 AWG | 0.0962 | 85-100A feeders |
| 2 AWG | 0.1146 | 95-115A feeders, service entrance |
| 1 AWG | 0.1534 | 110-130A feeders |
| 1/0 AWG | 0.1825 | 125-150A service entrance, large feeders |
| 2/0 AWG | 0.2190 | 145-175A service entrance |
| 3/0 AWG | 0.2642 | 165-200A service entrance |
| 4/0 AWG | 0.3197 | 195-230A main service entrance |
| 250 AWG | 0.3904 | 215-255A large services |
| 300 AWG | 0.4536 | 240-285A commercial services |
| 350 AWG | 0.5166 | 260-310A commercial services |
| 400 AWG | 0.5782 | 280-335A commercial/industrial |
| 500 AWG | 0.6984 | 305-380A large industrial feeders |
Minimum Conduit Size for XHHW Conductors
The table below shows the minimum conduit trade size needed for various numbers of XHHW conductors in EMT conduit. This is the most commonly referenced conduit type. For other conduit types, use the calculator or browse the individual conduit type pages.
| Wire Size | 3 wires | 4 wires | 6 wires | 8 wires | 10 wires | 12 wires |
|---|---|---|---|---|---|---|
| 14 AWG | 1/2" | 1/2" | 1/2" | 1/2" | 3/4" | 3/4" |
| 12 AWG | 1/2" | 1/2" | 1/2" | 3/4" | 3/4" | 1" |
| 10 AWG | 1/2" | 1/2" | 3/4" | 3/4" | 1" | 1" |
| 8 AWG | 3/4" | 3/4" | 1" | 1-1/4" | 1-1/4" | 1-1/4" |
| 6 AWG | 3/4" | 1" | 1-1/4" | 1-1/4" | 1-1/4" | 1-1/2" |
| 4 AWG | 1" | 1" | 1-1/4" | 1-1/2" | 1-1/2" | 2" |
| 3 AWG | 1" | 1-1/4" | 1-1/4" | 1-1/2" | 2" | 2" |
| 2 AWG | 1" | 1-1/4" | 1-1/2" | 2" | 2" | 2-1/2" |
| 1 AWG | 1-1/4" | 1-1/2" | 2" | 2" | 2-1/2" | 2-1/2" |
| 1/0 AWG | 1-1/4" | 1-1/2" | 2" | 2-1/2" | 2-1/2" | 2-1/2" |
| 2/0 AWG | 1-1/2" | 2" | 2" | 2-1/2" | 2-1/2" | 3" |
| 3/0 AWG | 1-1/2" | 2" | 2-1/2" | 2-1/2" | 3" | 3" |
| 4/0 AWG | 2" | 2" | 2-1/2" | 3" | 3" | 3-1/2" |
| 250 AWG | 2" | 2-1/2" | 2-1/2" | 3" | 3-1/2" | 4" |
| 300 AWG | 2-1/2" | 2-1/2" | 3" | 3-1/2" | 3-1/2" | 4" |
| 350 AWG | 2-1/2" | 2-1/2" | 3" | 3-1/2" | 4" | N/A |
| 400 AWG | 2-1/2" | 2-1/2" | 3" | 4" | 4" | N/A |
| 500 AWG | 2-1/2" | 3" | 3-1/2" | 4" | N/A | N/A |
About XHHW Conductors
XHHW is commonly used in industrial power distribution, large feeder circuits, and applications requiring superior heat resistance. It is particularly favored for service entrance conductors, switchgear wiring, and medium-voltage applications. The cross-linked polyethylene insulation provides excellent performance in high-temperature environments such as engine rooms, boiler rooms, and industrial process areas where ambient temperatures are elevated.
Insulation Details
XHHW uses cross-linked polyethylene (XLPE) insulation, which is a thermoset material. Unlike thermoplastic PVC insulation (used in THHN), XLPE will not melt or flow at elevated temperatures because the cross-linking creates permanent molecular bonds. This gives XHHW superior performance in high-heat applications but results in a slightly larger insulation diameter compared to THHN for the same wire gauge, meaning fewer conductors fit in the same conduit size.
History and Development
XHHW was developed as cross-linked polyethylene technology became commercially viable for wire insulation in the 1960s and 1970s. The cross-linking process, which uses either chemical agents or electron-beam irradiation, fundamentally changes the polymer from a thermoplastic to a thermoset, providing superior high-temperature performance. XHHW has become the standard for high-performance industrial wiring applications.
Advantages of XHHW
- Thermoset insulation will not melt or flow at high temperatures
- Excellent moisture resistance for wet and damp locations
- Superior chemical resistance compared to PVC-based insulations
- Better performance in high-ambient-temperature environments
- Longer service life in demanding industrial applications
- Available in XHHW-2 variant with 90 degrees C wet rating
Limitations
- Larger insulation diameter than THHN, reducing conduit fill counts
- Higher cost per foot than THHN/THWN-2
- No nylon jacket means less abrasion resistance during pulling
- Less flexible than THHN at room temperature
- Not as widely stocked as THHN at general electrical suppliers
Other Wire Types
Compare conduit fill with other conductor insulation types. Different insulation materials have different thicknesses, which affects how many conductors fit in a given conduit.