Beginner
Sky High Car Audio
Sky High E-Series big 3, CCA
$32.95The cheapest way to do the big 3 properly, and copper clad aluminum at 1/0 still beats factory 6 gauge by a wide margin.
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Big 3 Upgrade Wire Size Calculator
Quick answer
The big 3 is three cables sized to carry the alternator full output. A 150 amp alternator needs 1/0 gauge on all three runs to hold voltage drop under 2 percent over a typical 4 foot engine bay route, and all three are added alongside the factory cables rather than replacing them.
Result
Wire size for all three runs 1/0 AWG Published figure
Alternator output 150 A
Voltage drop at full output 0.146 V Published figure
Fuse for the alternator run 150 A Published figure
The three runs are: alternator positive to battery positive, battery negative to chassis, and engine block to chassis. The engine to chassis strap is the one people skip and it is often the worst connection in the car.
The formula
Size each of the three runs for the alternator rated output at the target voltage drop
The big 3 does not add power. It removes resistance from paths the factory sized for a stock electrical load, so the voltage at the amplifier stops sagging. Add the new cables in parallel with the factory ones rather than cutting anything out, and fuse the alternator run near the alternator.
The figures above are computed with these exact inputs: Alternator output 150 A, Longest run, one way 4 ft, Maximum voltage drop 2 %.
What this calculator assumes
Some of these are published physics or manufacturer figures and some are conventions. They are not the same kind of number, so each one is labeled.
| Assumption | Kind | Where it comes from |
|---|---|---|
| NEC Chapter 9 | Published figure | NEC Chapter 9, Table 8, uncoated stranded copper at 75 C |
| NEC Table 310.16 | Published figure | NEC Table 310.16, 75 C copper |
Gear that matches this result
Every card below is in the page source. The calculator re-ranks them against your numbers and marks anything that falls short of what you just calculated.
Intermediate
HiFind
True Spec oversized 1/0 OFC big 3
$82.99Oxygen free copper at a price closer to the CCA kits than most OFC options.
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Sky High Car Audio
Sky High 1/0 OFC big 3
$96.95Pre-terminated OFC in red and black, which saves buying lugs and a crimper for a first upgrade.
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RECOIL
Recoil PBG3 1/0 OFC
$105.00Full OFC with the terminals already crimped, which removes the one step that is easy to do badly.
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NVX
NVX True Spec 1/0 100 percent OFC
$119.99A hundred percent OFC at true 1/0, which is the version to buy if a high output alternator is coming next.
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Elite Audio
Elite Audio 0 gauge big 3
$124.99Full spec OFC rated for a 4,000 watt system.
Check price on AmazonFrequently asked questions
- How does the big 3 wire size calculation work?
- Size each of the three runs for the alternator rated output at the target voltage drop. The big 3 does not add power. It removes resistance from paths the factory sized for a stock electrical load, so the voltage at the amplifier stops sagging. Add the new cables in parallel with the factory ones rather than cutting anything out, and fuse the alternator run near the alternator.
- Are these figures published or are they rules of thumb?
- Both, and the page labels which is which. The Helmholtz port relation, the Thiele/Small alignment equations, cone area geometry, Ohm’s law, conductor resistance and ampacity, and manufacturer specifications are published and are labeled as such. Amplifier efficiency, cabin gain, the farad per thousand watts rule, port area per cubic foot and coverage percentages are conventions with no measurement behind them, and they are labeled as conventions.
- Why does this calculator sometimes refuse to give an answer?
- Because there genuinely is not one. A port can be too large in area for the box and tuning asked of it, a vented alignment stops describing a useful box outside a Qts range, and a sealed box cannot produce a total Q below the driver’s own. In each case the calculator returns nothing and explains why, rather than extrapolating past the end of a published relation.
- Do I still need an installer if I use this?
- Many owners do their own 12V work, and these are the figures that work is sized from. What matters is that a car battery delivers hundreds of amps into a short without hesitating, so the main fuse goes within 18 inches of the battery positive terminal and the battery comes off before power wire goes in. If any of that is beyond what you want to take on, a professional installer is money well spent.
Researched guidance, not professional advice. These results are planning figures from published relations and manufacturer specifications. Fit the main fuse within 18 inches of the battery positive terminal, because that fuse protects the wire and the wire is what starts a fire. Disconnect the battery before running power wire, use a grommet through every piece of sheet metal, and remember that sustained high sound pressure causes permanent hearing damage.