Big 3 upgrade: what gauge wire?
Size the Big 3 for your alternator’s full output: 2 AWG copper for a 150 A alternator, 1/0 AWG for 220 A. Never use thinner wire than your amp’s power wire.
The Big 3 replaces three factory cables so the alternator’s current reaches the battery and the body with less loss: lights dim less on bass notes and the amps see higher voltage.
Big 3 wire gauge by alternator output
Big 3 wire gauge by alternator output| Alternator | Copper (OFC) | CCA (aluminum) |
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| 90 A | 6 | 4 |
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| 110 A | 4 | 2 |
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| 130 A | 4 | 2 |
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| 150 A | 2 | 1 |
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| 180 A | 1 | 1/0 |
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| 200 A | 1 | 2/0 |
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| 220 A | 1/0 | 2/0 |
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| 250 A | 2/0 | 3/0 |
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| 270 A | 2/0 | 4/0 |
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| 320 A | 3/0 | Over 4/0: ask an installer. |
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The three wires
1. Alternator positive to battery positive (fuse it near the battery at the alternator’s rating or the wire’s, whichever is lower).
2. Battery negative to the body or frame.
3. Engine block to the body or frame.
Same method as the wire calculator: the wire must carry the alternator’s full output (33 CFR 183.425, 105 °C, × 0.85 engine bay) with under 0.5 V drop over about 3 ft. Keep the factory cables and add the new ones if you like.
Guidance only, never a safety rating. Follow your amp and vehicle manuals. The fuse protects the wire: put it within 18 in of the battery. Disconnect the battery before you wire.
Frequently asked questions
Do I need the Big 3 upgrade?
Past about 1,000 W RMS, or if your lights dim on bass notes, it is the cheapest fix: it lets the alternator’s current reach the battery and the body.
Do I keep the factory cables?
You can: adding the new wires alongside them only lowers the resistance. Many installers replace them instead.
What gauge wire for the Big 3?
Size the Big 3 for your alternator’s full output: 2 AWG copper for a 150 A alternator, 1/0 AWG for 220 A. Never use thinner wire than your amp’s power wire.