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.
Buy silicone-insulated, finely-stranded copper. Silicone stays flexible and survives 180–200 °C; PVC hardens and cracks with vibration. Avoid copper-clad aluminium entirely — it is sold cheaply as "CCA" and has around 60% of copper's conductivity, so it needs two gauges thicker to match, and it work-hardens and breaks at crimps.
Two limits, not one
Every conductor faces two separate constraints and either can decide the answer. The thermal limit is how much current the wire carries before its insulation cooks. The voltage drop limit is how much of your pack voltage the cable eats before it reaches the load, and it scales with length.
On short scooter runs the thermal limit usually wins — a 30 cm battery lead at 40 A barely drops any voltage, but it still needs enough copper to carry 40 A without melting. On long runs, drop takes over. Sizing on one and ignoring the other is the most common wiring mistake in DIY builds, which is why this calculator applies both and tells you which one is deciding.
| 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. AWG also runs backwards: a smaller number means thicker wire, and every three gauges roughly doubles the cross-sectional area.
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") carries about 60% of copper's current for the same size 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.
Size the wiring for what the pack can actually deliver — which the pack calculator tells you — not for what the old pack managed.
Questions riders actually ask
What gauge wire do I need for 30 amps?
On a 48 V system at 3% drop, 12 AWG covers anything up to about 3 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. This calculator uses the standard 20 °C figures, so add margin for wiring that runs hot inside a sealed deck.