USE-2 Conduit Fill Guide
Underground Service Entrance cable, 90 degrees C rating (USE-2) conductors are rated for 90 degrees C (194 degrees F). This page provides complete conduit fill data for USE-2 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.
USE-2 Conductor Specifications
USE-2 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 USE-2 Conductors
The table below shows the minimum conduit trade size needed for various numbers of USE-2 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 USE-2 Conductors
USE-2 is specifically designed for underground service entrance applications and direct burial installations. It is the standard conductor for running power from the utility transformer pad to the building's meter base or service disconnect. USE-2 is also used for underground feeder circuits, outdoor lighting circuits, and any application requiring direct burial without conduit. When installed in conduit, USE-2 can be used in the same manner as other building wire types.
Insulation Details
USE-2 uses cross-linked polyethylene (XLPE) insulation that is specifically formulated for underground and direct burial applications. The insulation is rated for continuous contact with soil and moisture, and is resistant to the chemicals and organisms found in underground environments. USE-2 insulation dimensions are identical to XHHW, as both use XLPE, but USE-2 carries specific listings for direct burial and underground use.
History and Development
USE cable has been part of the NEC for decades as the standard for underground service entrance installations. The -2 suffix indicates the 90 degrees C temperature rating, which was added as insulation technology improved. USE-2 is often dual-rated with RHW-2 or XHHW-2, allowing a single conductor to serve multiple purposes and simplifying inventory management for contractors.
Advantages of USE-2
- Rated for direct burial without conduit
- 90 degrees C temperature rating in wet and dry locations
- Excellent moisture and soil chemical resistance
- Sunlight-resistant for exposed outdoor sections
- Often dual-rated with XHHW-2 or RHW-2 for versatility
- Long service life in underground applications
Limitations
- Larger insulation diameter than THHN, reducing conduit fill counts
- Higher cost than standard building wire types
- Not listed as interior building wire unless it also carries a building wire rating (dual-rated)
- Same conduit fill dimensions as XHHW, fewer conductors per conduit than THHN
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.