Guide Topics
100 Amp Wire Size Guide
Complete specifications for 100 A service entrance
Quick Answer: Wire Size for 100 Amp Service
For a 100 A dwelling service or main power feeder, use 4 AWG copper or 2 AWG aluminum (2023 NEC Table 310.12). A service needs a grounding electrode conductor: 8 AWG copper or 6 AWG aluminum (NEC Table 250.66, values from NFPA's 2020 grounding fact sheet). If these conductors are the main power feeder, they carry an equipment grounding conductor instead: 8 AWG copper or 6 AWG aluminum (NEC Table 250.122). A feeder to a subpanel is sized from NEC Table 310.16: see the wire size calculator.
Common 100 Amp Applications
Main Service
Small home main panel
Installation Requirements & Code References
| Component | Specification | NEC Reference |
|---|---|---|
| Main Breaker | 100 A 2-pole breaker | NEC 230.79 |
| Wire Size (Copper) | 4 AWG (100 A dwelling service) | NEC Table 310.12 |
| Wire Size (Aluminum) | 2 AWG (100 A dwelling service) | NEC Table 310.12 |
| Equipment grounding conductor (main power feeder) | 8 AWG copper | NEC Table 250.122 |
| Grounding electrode conductor (service) | 8 AWG copper | NEC Table 250.66 |
Step-by-Step Installation Guide
- 1
Calculate Load Requirements
Verify that 100 A is sufficient for your needs using NEC Article 220 load calculations.
- 2
Measure Distance
Measure the actual wire run distance including vertical runs and bends.
- 3
Select Wire Size
Choose wire based on distance: 4 AWG copper or 2 AWG aluminum for a 100 A dwelling service (Table 310.12), upsize for longer distances.
- 4
Install Conduit
Run conduit for the two ungrounded conductors and the neutral, plus an equipment grounding conductor if the run is the main power feeder.
- 5
Pull Conductors
Pull THHN/THWN-2 conductors through conduit, maintain proper color coding.
- 6
Make Terminations
Use proper torque specs.
- 7
Install Grounding System
Connect the 8 AWG copper grounding electrode conductor at the service, or the 8 AWG copper equipment grounding conductor on the main power feeder.
- 8
Test & Inspect
Test insulation resistance, verify connections, and schedule inspection.
Temperature & Environmental Factors
High Temperature Areas
- Attics at 41–45 °C (105–113 °F): 0.82 in the 75 °C column (Table 310.15(B)(1)(1))
- Consider upsizing wire for extreme heat conditions
Wet Locations
- Use THWN-2 or XHHW for wet locations
- Underground: USE-2 or direct burial cable
- Schedule 80 PVC for physical protection
Related Calculators
Common Mistakes to Avoid
Sizing Errors
- ❌ Forgetting voltage drop for long runs
Installation Errors
- ❌ Undersized conduit causing difficult pulls
- ❌ Incorrect torque on terminals
- ❌ Wrong ground wire size (10 AWG instead of 8 AWG)