3 AWG Copper vs Aluminum
At 3 AWG, aluminum wire carries 25% less current than copper but costs roughly 40-60% less per foot and weighs one-third as much. With copper prices rising, 3 AWG aluminum wire is increasingly common for feeders and service entrances where the cost savings are substantial.
Ampacity comparison
All values per NEC 2023 Table 310.16 for THHN insulation with 110.14(C) termination limits applied.
| Property | Copper | Aluminum |
|---|---|---|
| 90°C ampacity | 115A | 85A |
| Usable (after 110.14(C)) | 100A | 75A |
| Breaker | 100A | 80A |
| Conduit (EMT) | 1" EMT | 1" EMT |
Voltage drop comparison
Voltage drop at 75A load (limited by aluminum capacity) on 240V single-phase.
| Distance | Copper | Aluminum |
|---|---|---|
| 50 ft | 0.8% | 1.3% |
| 75 ft | 1.1% | 1.9% |
| 100 ft | 1.5% | 2.5% |
| 150 ft | 2.3% | 3.8% |
| 200 ft | 3.1% | 5.0% |
When to use each
Use 3 AWG copper when
- You need the full 100A capacity in a single conductor
- Terminal connections are standard (most residential equipment is copper-only rated)
- Space is limited and you need the smallest conduit possible
- Connections will not be accessible for periodic retorquing
Use 3 AWG aluminum when
- 75A is sufficient for your load
- All terminals are AL-rated (marked AL/CU or AL)
- Anti-oxidant compound will be applied at every connection
- Cost savings justify the extra installation care
What to buy
At 3 AWG, aluminum is the industry default for feeders and service entrance conductors. Material savings are substantial: roughly half the per-foot cost of copper. Buy AA-8000 series aluminum. For service entrance, SER cable bundles conductors with a bare ground. For conduit, buy individual THHN or XHHW-2. Anti-oxidant compound and a calibrated torque wrench are mandatory accessories at this size.
Common products for 3 AWG Copper circuits
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Detailed ampacity: 3 AWG copper, 3 AWG aluminum. Wire size lookup: 100A circuit.
Frequently asked questions
Is 3 AWG aluminum safe to use?
Yes, when installed correctly. 3 AWG aluminum carries 75A and is common in feeder circuits. Use AL-rated terminals, apply anti-oxidant compound, and torque connections to manufacturer specs. Modern AA-8000 series aluminum is engineered for building wire.
How much less does 3 AWG aluminum carry than copper?
3 AWG aluminum carries 75A vs 100A for copper, a 25A difference (25% reduction). To match copper ampacity, you typically need to go up 2 gauge sizes in aluminum.
What size aluminum equals 3 AWG copper?
To match 3 AWG copper (100A), check the 100A wire size guide for the exact aluminum equivalent needed.
Can I mix copper and aluminum in the same circuit?
Not directly. Copper and aluminum must not touch at connections due to galvanic corrosion. Use approved bimetallic connectors (like Alumiconn) or AL/CU-rated panel lugs.
NEC 2023 references verified April 2026