Battery Cable Sizing for Van & RV Builds (AWG Guide)
Battery cable sizing is the most consequential wiring decision in a van build. Undersized cables get hot, lose voltage, and can cause fires. Here's how to size them correctly.
The two factors: ampacity and voltage drop
Ampacity is the maximum current a wire can carry without overheating. AWG (American Wire Gauge) ratings reflect this.
Voltage drop is how much voltage is lost across the cable at a given current. At 12V, even a 0.5V drop is a significant percentage of system voltage. Long runs need thicker wire even if the ampacity rating would allow thinner.
Main battery cable (battery to positive bus bar)
This cable carries the sum of all charging inputs and load outputs — your total system current.
Step 1: Identify your peak current. The main contributors:
- 2,000W inverter at full load: ~185A at 12V
- 3,000W inverter at full load: ~275A at 12V
- DC-DC charger (60A): 60A
- MPPT solar (50A): 50A
For most van builds with a 2,000W inverter: peak current ~185–220A (inverter dominates; other sources add current, other loads reduce battery draw).
Step 2: Select AWG based on ampacity + run length:
| AWG | Ampacity (60°C) | Max run at 2% drop / 150A |
|---|---|---|
| 4 AWG | 85A | ~1.5 ft |
| 2 AWG | 115A | ~2.5 ft |
| 1/0 AWG | 150A | ~4 ft |
| 2/0 AWG | 175A | ~5 ft |
| 4/0 AWG | 230A | ~8 ft |
For a 2,000W inverter with a 3-foot main cable run (battery to bus bar): 2/0 AWG is the standard choice.
Inverter cable
The cable from battery positive (or positive bus bar) to the inverter typically carries the highest current in the system. Run it as short as physically possible — mount the inverter close to the battery.
| Inverter size | Cable AWG | Max run length |
|---|---|---|
| 1,000W | 1/0 AWG | 4 ft |
| 2,000W | 2/0 AWG | 4 ft |
| 2,000W | 4/0 AWG | 8 ft |
| 3,000W | 4/0 AWG | 4 ft |
Always use the AWG specified by your inverter manufacturer. Most quality inverters include cable size recommendations in their documentation.
DC-DC charger cable
A 40A DC-DC charger draws 40A from the alternator (starter battery side) and pushes 40–60A to the house battery side. Both cables need appropriate sizing:
- Alternator/starter side: 8 AWG handles 40A continuous with some margin
- House battery side: 8 AWG for 40A, 6 AWG for 60A
Both cables need fuses within 18" of each battery terminal.
MPPT solar controller cables
- PV input cable (panels to MPPT): 10 AWG is standard — handles 30A PV current across typical roof-to-controller runs
- Battery output cable (MPPT to bus bar): 10 AWG for 30A controllers; 8 AWG for 50A controllers
Parallel battery interconnects
If you wire two batteries in parallel (two 100Ah batteries for 200Ah total), the interconnect cable should be as short as possible and sized for the maximum current that could flow between them — typically 2/0 AWG for lithium builds.
A note on welding cable vs battery cable
Both work. Welding cable (SAE J1127) is more flexible, easier to route, and available cheaply at welding supply stores. Marine-rated battery cable (ABYC A-30) is appropriate for RV applications and often used in marine/RV supply stores. Avoid automotive primary wire for high-current battery cables — it's rated for 60°C continuous use, which is marginal for high-current van applications.