What Wire Size for a 100 Amp Sub Panel? NEC Feeder Requirements 2026
A 100 amp sub panel requires 1 AWG copper or 1/0 AWG aluminum wire per NEC Table 310.16 (75°C column). You must run 4 conductors: two hot wires, one neutral, and one equipment ground. The neutral and ground must be separated (not bonded) in the sub panel, and a grounding electrode is required at the sub panel location per NEC 250.32.
NEC Requirements for 100A Sub Panel Feeders
Per NEC 215.2, feeder conductors must have an ampacity not less than the load served. For a 100A sub panel, the feeder conductors must be rated for at least 100 amps. NEC Table 310.16 at the 75°C column gives us: 1 AWG copper at 130A or 1/0 AWG aluminum at 120A. Both exceed 100A and are the standard choices. Note: some electricians prefer 2 AWG copper (rated 115A at 75°C) for short runs, which is also code-compliant.
Why 4 Conductors? The Sub Panel Grounding Rule
NEC 250.32(B) requires that a sub panel in a separate structure (or a remote panel) must have the neutral and ground separated. This means you cannot bond the neutral bar to the ground bar in the sub panel — unlike the main panel where they are bonded. You must run 4 separate conductors: Line 1 (hot), Line 2 (hot), Neutral, and Equipment Grounding Conductor (EGC). The EGC must be sized per NEC Table 250.122: 8 AWG copper for a 100A feeder.
Wire Size by Distance (Voltage Drop)
For runs under 50 feet, standard 1 AWG copper is sufficient. For 50-100 feet, consider upsizing to 1/0 AWG copper. For 100-150 feet, use 2/0 AWG. For 150-200 feet, use 3/0 AWG. For 200+ feet, use 4/0 AWG or consider stepping up to higher voltage distribution. These recommendations keep voltage drop under 3% at full 100A load. For actual loads less than 100A, you may be able to use smaller wire — verify with our Voltage Drop Calculator.
Copper vs Aluminum for Sub Panel Feeders
Aluminum is commonly used for sub panel feeders because it's significantly cheaper for large wire sizes and is well-suited for this application. For a 100A feed: 1/0 aluminum costs roughly 40% less than 1 AWG copper. Since sub panel feeders connect at lugs (not small device terminals), the connection concerns with aluminum are minimal. Most sub panels have AL/CU-rated lugs. Apply anti-oxidant compound and torque to manufacturer specs. SER (Service Entrance cable) with aluminum conductors is the most popular choice.
| Distance | Copper | Aluminum | Voltage Drop |
|---|---|---|---|
| 0-50 ft | 1 AWG | 1/0 AWG | < 1.5% |
| 50-100 ft | 1/0 AWG | 2/0 AWG | < 3.0% |
| 100-150 ft | 2/0 AWG | 3/0 AWG | < 3.0% |
| 150-200 ft | 3/0 AWG | 4/0 AWG | < 3.0% |
| 200+ ft | 4/0 AWG | 250 MCM | < 3.0% |
Installation Checklist
1. Main panel breaker: Install a 100A double-pole breaker in the main panel. 2. Feeder cable: Run 4-conductor SER cable or individual THHN in conduit. 3. Sub panel mounting: Mount at eye level with 36" clear working space (NEC 110.26). 4. Neutral isolation: Remove the bonding screw/strap — separate neutral and ground bars. 5. Grounding electrode: Install a ground rod at the sub panel per NEC 250.32(A). 6. Labeling: Label the sub panel with the location of the main disconnect per NEC 408.4.
Disclaimer: This article is for educational reference only. Consult a licensed professional for all electrical work and solar installations.