Service entrance wire size for 100 to 400 amps
NEC 310.12 lets the main power feeder or service conductors of a single-phase, 120/240 V dwelling be smaller than the usual ampacity tables, because dwellings rarely load every circuit at once. This is often called the 83% rule. It applies to the service conductors and feeders carrying the whole load of a one-family home, and it is for 100 to 400 A only.
| Service | Copper | Aluminum or copper-clad | Ground rod wire (copper) |
|---|---|---|---|
| 100 A | 4 AWG | 2 AWG | 8 AWG |
| 110 A | 3 AWG | 1 AWG | 8 AWG |
| 125 A | 2 AWG | 1/0 AWG | 8 AWG |
| 150 A | 1 AWG | 2/0 AWG | 6 AWG |
| 175 A | 1/0 AWG | 3/0 AWG | 6 AWG |
| 200 A | 2/0 AWG | 4/0 AWG | 4 AWG |
| 225 A | 3/0 AWG | 250 kcmil | 4 AWG |
| 250 A | 4/0 AWG | 300 kcmil | 2 AWG |
| 300 A | 250 kcmil | 350 kcmil | 2 AWG |
| 350 A | 350 kcmil | 500 kcmil | 2 AWG |
| 400 A | 400 kcmil | 600 kcmil | 1/0 AWG |
The last column is the grounding electrode conductor from NEC Table 250.66, sized from the copper service conductors. If it only goes to a ground rod, 250.66(A) does not require more than 6 AWG copper. To a concrete-encased electrode, 4 AWG copper is the most required.
200 amp service wire size
- Copper: 2/0 AWG
- Aluminum: 4/0 AWG
- Ground to the electrode: 4 AWG copper (2 AWG aluminum)
- Equipment ground for the 200 A breaker: 6 AWG copper, 4 AWG aluminum, from Table 250.122
When the 83% rule does not apply
Outside a single-family dwelling service or feeder, size by the ampacity table. 200 A needs 3/0 copper (200 A at 75°C) or 250 kcmil aluminum (205 A) in that case. This also applies to a 200 A sub panel feeder to a detached building, and to any three-phase or commercial service.
| Case | Copper | Aluminum |
|---|---|---|
| Single-family dwelling service (310.12) | 2/0 AWG | 4/0 AWG |
| Any other 200 A feeder (310.16, 75°C) | 3/0 AWG | 250 kcmil |
Voltage drop on a long service run
A 200 A load at 240 V on 2/0 copper stays within 3% for about 186 ft one way. On 4/0 aluminum the limit is about 180 ft. A service lateral longer than that should be upsized. The ground wire then increases in proportion, under NEC 250.122(B). Check your numbers with the voltage drop calculator.
For smaller breakers, see the breaker to wire size chart.
Frequently asked questions
What size wire for 200 amp service?
2/0 copper or 4/0 aluminum for a single-phase dwelling service under NEC 310.12. Any other 200 A feeder needs 3/0 copper or 250 kcmil aluminum.
What size ground wire for 200 amp service?
4 AWG copper to the grounding electrode, when the service conductors are 2/0 copper. If it connects only to a ground rod, 6 AWG copper is enough.
What size wire for a 100 amp service?
4 AWG copper or 2 AWG aluminum for a single-phase dwelling.
What size wire for a 200 amp sub panel?
3/0 copper or 250 kcmil aluminum. The dwelling 83% rule does not apply to a sub panel in a detached building.
What size conduit for 200 amp service?
Typically 2 inch for 2/0 or 4/0 conductors, but conduit fill depends on the wire type and the number of conductors. Confirm with the NEC Annex C tables or your inspector.
Sources
- NFPA 70, National Electrical Code (NEC)
- NFPA: Understanding NFPA 70 (free read-only access)
- Electrical Training Alliance and NEC table summaries are reference only; read NEC 310.12 in the current edition