Enter your current, one-way run length, system voltage and the voltage drop you can accept, and this calculator returns the smallest safe copper gauge, the actual drop, and the power you will lose as heat in the cable.
What gauge wire do you need for 30 amps?
On a 48 V system with a 3% voltage-drop budget, 12 AWG covers runs up to about 4 m and has the heat rating for 30 A continuous. Longer runs need thicker wire: 10 AWG at 5 m and 8 AWG at 8 m. Current, run length and acceptable drop decide the size together.
Voltage drop, not just current rating
Two separate limits apply to any conductor, and either one can decide the answer. The first is thermal: how much current the wire carries before its insulation cooks. The second is voltage drop over the length of the run, which scales with length — so a gauge that is fine for 30 cm is inadequate at 3 m. Short scooter runs are usually decided by heat, long runs by drop, and sizing on one while ignoring the other is the classic DIY wiring mistake.
Drop is Ohm's law over the round trip: V = I × R, where R is resistance per metre × twice your one-way length, because current returns through the negative conductor. Every volt lost in the cable is a volt the motor never sees and a watt of heat in your loom.
How much drop is acceptable
For motor and battery main runs, aim for 2–3% at continuous current. Lighting and low-power accessories tolerate 5%. Below 3% you get consistent performance and cool cabling; above 5% you get noticeable power loss, warm wires and connectors that degrade over time.
Low-voltage systems are far less forgiving in percentage terms. A 1 V drop on a 36 V scooter is 2.8%; the same 1 V on a 400 V car pack is 0.25%. This is exactly why performance builds moved to higher voltages — the same power moves through the wiring with proportionally less loss.
AWG, mm² and choosing real cable
AWG runs backwards: smaller number means thicker wire, and every 3 gauges roughly doubles cross-sectional area. The common EV sizes are 12 AWG (3.3 mm²) for accessories, 10 AWG (5.3 mm²) for moderate motor runs, 8 AWG (8.4 mm²) for high-power phase wires and 4 AWG (21 mm²) or larger for battery mains.
| AWG | mm² | mΩ per metre | Chassis rating | Typical use |
|---|---|---|---|---|
| 4/0 | 107.2 | 0.161 | 380 A | High-power inverter mains |
| 2/0 | 67.4 | 0.256 | 283 A | Large EV battery mains |
| 2 | 33.6 | 0.513 | 181 A | Performance scooter mains |
| 4 | 21.2 | 0.815 | 135 A | Battery mains, big builds |
| 6 | 13.3 | 1.296 | 101 A | Dual motor phase wires |
| 8 | 8.37 | 2.061 | 73 A | High-power phase wires |
| 10 | 5.26 | 3.277 | 55 A | Moderate motor runs |
| 12 | 3.31 | 5.211 | 41 A | Commuter scooter phases |
| 14 | 2.08 | 8.286 | 32 A | Light motor, heavy accessories |
| 16 | 1.31 | 13.17 | 22 A | Lighting, horns, controls |
| 18 | 0.823 | 20.95 | 16 A | Signal and sensor wiring |
| 20 | 0.518 | 33.31 | 11 A | Hall sensors, throttle |
Chassis ratings assume a single conductor in free air with high-temperature insulation. Bundled inside a sealed deck, in conduit, or at high ambient temperature, derate substantially — 30–50% is not unusual.
Buying cable that lasts
- Silicone insulation, finely stranded. It stays flexible and survives 180–200 °C; PVC hardens and cracks with vibration.
- Real copper only. Copper-clad aluminium (“CCA”) has about 60% of copper’s conductivity, so it needs to be two gauges thicker to match — and it work-hardens and breaks at crimps.
- Match the connector to the cable. An XT60 on 8 AWG is a bottleneck; the connector rating is part of the circuit.
- Crimp properly, then heatshrink. A cold solder joint on a vibrating scooter is a future open circuit.
- Fuse the battery main. Everything downstream depends on it, and a shorted phase wire will happily draw hundreds of amps.
How the calculator works
For each gauge, the calculator works out the voltage dropped over the round trip at your current, adjusted for conductor material and wire temperature. It then recommends the thinnest gauge that passes two tests: the drop stays inside your budget, and the wire’s free-air rating is at least 25% above your continuous current. It also tells you which of the two tests decided the answer.
The formula
drop % = Vdrop ÷ Vsystem × 100
Plost = Vdrop × I // watts turned into heat
drop % ≤ your budget and ampacity ≥ I × 1.25
Related calculators
Wire is sized around the current the pack can deliver, so start with the battery pack calculator. A steep climb is where that current peaks, and the hill climb calculator shows how high it goes on your gradient.
Questions riders actually ask
What gauge wire do I need for 30 amps?
On a 48 V system at 3% drop, 12 AWG covers runs up to about 4 m — and 12 AWG is also the thinnest gauge with the thermal headroom for 30 A continuously. At 5 m you need 10 AWG, and at 8 m, 8 AWG. Current alone never answers the question: length, acceptable drop and the wire's own heat rating all have to be part of it.
What happens if my wire is too thin?
It heats up, which raises its resistance, which makes it heat further. Mild cases lose power and sag voltage under load. Serious cases melt insulation, damage connectors and start fires. Thin wire is the most common cause of scooter wiring failures after water ingress.
Do I calculate for one-way or round-trip length?
Enter the one-way distance — the calculator doubles it, because current has to return through the negative conductor. Forgetting the return path is the classic mistake and understates the drop by exactly half.
How do I convert AWG to mm²?
Common equivalents: 16 AWG = 1.31 mm², 14 = 2.08, 12 = 3.31, 10 = 5.26, 8 = 8.37, 6 = 13.3, 4 = 21.2, 2 = 33.6. There is no clean formula in your head — the results table here lists both so you can order cable in either system.
Should I size for continuous or peak current?
Size for continuous current, then check that peak current does not exceed the wire's thermal rating for the few seconds it lasts. A cable good for 40 A continuous will survive 80 A for short bursts; the same cable at 80 A for a two-minute climb will not.
Does wire temperature change the result?
Yes. Copper resistance rises roughly 0.4% per °C, so a cable at 80 °C has about 24% more resistance than at 20 °C. The wire temperature setting in this calculator applies that correction — choose 80 °C for wiring that runs hot inside a sealed deck.
Sources
Primary and reference sources for the physics, standards and figures used on this page.
- American wire gaugeWikipedia