What Size Conduit for a 100-Amp Service?
For a 100A residential service with 4 AWG copper or 2 AWG aluminum conductors, use 1-1/4-inch EMT minimum.
For a 100-amp residential service entrance, conduit sizing depends on whether you're using the NEC 310.12 dwelling exception or standard Table 310.16:
| Conductors used | Service raceway | Standard size |
|---|---|---|
| 4 AWG copper (310.12 dwelling) | EMT / IMC / PVC | 1-1/4 inch |
| 3 AWG copper (310.16 standard) | EMT / IMC / PVC | 1 inch |
| 2 AWG aluminum (310.12 dwelling) | EMT / IMC / PVC | 1-1/4 inch |
| 1 AWG aluminum (310.16 standard) | EMT / IMC / PVC | 1-1/4 inch |
The math (100A service, 4 AWG copper dwelling rule)
| Variable | Value |
|---|---|
| 4 AWG THHN conductor area | 0.0824 in² |
| Conductors (2 hots + 1 neutral) | 3 |
| Total conductor area | 0.247 in² |
| Required @ 40% fill | 0.617 in² |
Conduit options meeting the 0.617 in² minimum interior area:
- 3/4" EMT (0.533 in²) — fails (46.4% fill)
- 1" EMT (0.864 in²) — fits at 28.6%, could work if no EGC added
- 1-1/4" EMT (1.496 in²) — fits at 16.5%, standard choice with EGC included
Most installations include the equipment grounding conductor (8 AWG for 100A circuits per NEC 250.122), bringing total to 4 conductors. 4 × 0.0824 + 1 × 0.0366 = adds 0.0366 in² → 1" EMT fills to 32.9% — still passes but tight.
Common configurations
Overhead service drop, riser to meter
- 2 × 4 AWG hots
- 1 × 4 AWG neutral
- No EGC in service entrance (bonded at first disconnect)
Goes in 1-1/4" EMT typically; can squeeze into 1" EMT if the run is short and straight.
Underground service lateral (PVC)
- 2 × 2 AWG aluminum hots
- 1 × 2 AWG aluminum neutral
- No EGC
Goes in 1-1/4" PVC Sch 80 for the exposed riser portion above grade; Sch 40 elsewhere underground.
Service entrance includes the GEC?
No. The grounding electrode conductor (GEC) typically runs separately from the service entrance, terminating at the ground rod or Ufer. The GEC is sized by NEC 250.66 (4 AWG copper for 100A service).
Quick reference
- Service entrance conduit: 1-1/4" EMT/RMC/PVC for 100A residential (4 AWG Cu or 2 AWG Al)
- Tight space option: 1" EMT with 3 AWG copper (NEC 310.16 standard)
- Underground risers: 1-1/4" PVC Sch 80 (above grade) → Sch 40 (below)
- Meter base / load center fittings: typically sized to match 1-1/4" hubs
For 200A service, see what size conduit for 200 amp service.