12V Wire Gauge & Fuse Sizing

Q: What wire gauge do I need for a 30A MPPT in my van?

For a 30A MPPT with a typical 3-5 meter run between MPPT and battery, use 6mm² (10 AWG) cable. For runs over 5m at 30A, step up to 10mm² (8 AWG) to keep voltage drop under 3%.

Q: What AWG cable do I need for a 1000W inverter in a van?

A 1000W inverter draws ~90A at 12V peak. Use 25mm² (4 AWG) for runs under 1m, 35mm² (2 AWG) for runs 1-2m. Inverter battery cables are always short — mount your inverter as close to your battery as possible.

Q: Can I use household lighting cable for van wiring?

No. Household cable (single-stranded, PVC rated for 230V AC) is not rated for the DC current levels in a 12V van system and is not flexible enough for vehicle use. Use flexible multi-strand automotive or marine-grade cable.

Q: How do I calculate voltage drop for a long cable run?

Voltage drop (V) = Current (A) × Cable length (m, one-way) × Resistance per meter (from specs). For 6mm² copper: 0.00327 Ω/m. A 30A run over 5m one-way: 30 × 5 × 0.00327 = 0.49V = 4.1% drop — exceed 3%, so step up to 10mm².

Prevent voltage drop and wire fires. Calculate the perfect wire gauge and fuse size for your campervan 12V electrical system.

Wiring is the most critical safety part of a van conversion. Get the exact wire section (mm²) and fuse rating for every appliance in your build.

⚡ Expert tip

Buy cable in bulk from an auto electrical supplier, not retail per-meter. Use marine-grade tinned copper cable — it resists corrosion in the humid van environment. The tinning layer preserves conductivity for 10+ years vs standard automotive cable that oxidizes.

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12V Cable Sizing Guide

Use this professional reference table to select the correct gauge (mm²) for your cables. For 12V in a van, the maximum tolerated voltage drop is 3%. Always use multi-stranded flexible automotive wire.

Current (A)	Round trip < 2m	Round trip 4m	Round trip 6m
5A (LEDs, USB)	1.5 mm²	2.5 mm²	4 mm²
10A (Fridge, Pump)	2.5 mm²	4 mm²	6 mm²
20A (Heater)	4 mm²	10 mm²	10 mm²
50A (DC/DC Booster)	10 mm²	16 mm²	25 mm²
100A (Inverter)	25 mm²	35 mm²	50 mm²

Fuse Sizing

The fuse protects the wire, not the appliance. Always place it as close to the power source as possible (battery or busbar).

Wire 1.5 mm² → Max fuse 10A
Wire 2.5 mm² → Max fuse 20A
Wire 4 mm² → Max fuse 30A
Wire 6 mm² → Max fuse 40A
Wire 10 mm² → Max fuse 60A

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Comparison table

Current	Length 1m	Length 2m	Length 5m	Length 10m
10A	18 AWG	18 AWG	16 AWG	14 AWG
20A	16 AWG	14 AWG	12 AWG	10 AWG
30A	14 AWG	12 AWG	10 AWG	8 AWG
50A	10 AWG	8 AWG	6 AWG	4 AWG
100A	6 AWG	4 AWG	2 AWG	1/0 AWG

About this tool

12V Wire Gauge Calculator for Van Life: AWG and mm² Sizing Guide

Undersized wiring is the #1 cause of electrical fires in van builds. A cable that's too thin for its current load heats up — sometimes to the point of melting insulation. Here's how to get wire sizing right every time.

The Two Factors That Determine Wire Gauge

Maximum current (amps) — from the device or circuit
Cable length (meters/feet) — longer cables = more resistance = more voltage drop

A cable that's fine for 3 meters might be dangerously undersized for 5 meters at the same current.

AWG to mm² Conversion and Current Ratings

AWG	mm²	Max Current (12V)	Typical Van Use
18 AWG	0.75 mm²	7A	LED lighting, small fans
16 AWG	1.5 mm²	13A	USB chargers, phones
14 AWG	2.5 mm²	20A	Water pump, tablet charging
12 AWG	4 mm²	30A	Fridge, laptop inverter
10 AWG	6 mm²	40A	Solar MPPT output, DC-DC charger
8 AWG	10 mm²	55A	Battery to inverter (short run)
4 AWG	25 mm²	100A	Battery main positive/negative
2/0 AWG	70 mm²	200A+	Large inverter battery cables

Current ratings for PVC-insulated cable at 40°C ambient. In hot engine bays or behind panels, derate by 20-30%.

The Voltage Drop Rule: Never Exceed 3%

Formula: Voltage drop (%) = (Current × Cable length × Resistance per meter) ÷ Battery voltage × 100

For a 12V system, 3% drop = 0.36V maximum. More than this and your devices may malfunction or cycle off unexpectedly. Fridges and inverters are particularly sensitive to low voltage.

Quick rule of thumb:

For runs under 3m: size for current alone
For runs 3-6m: go up one cable size
For runs over 6m: go up two cable sizes from the current-only recommendation

Fuse Sizing Rules

Every positive cable needs a fuse or circuit breaker as close to the battery as possible:

Fuse rating = 80-125% of expected cable current
Always fuse the cable, not the device

Example: 10 AWG (6mm²) cable rated for 40A → use a 40A or 50A fuse.

Expert tip: In a van build, buy cable in bulk from an auto electrical supplier, not at retail per-meter. Quality marine-grade tinned copper cable is worth the premium over standard automotive cable — it resists corrosion in the humid van environment and maintains conductivity for years.

Frequently asked questions

What wire gauge do I need for a 30A MPPT in my van?▼