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Don't cut a single wire until you have a complete diagram on paper. I know it's tempting to just start connecting things, but a wiring diagram is the difference between a build that works and one you're troubleshooting for weeks. Every professional installer starts here.
Your diagram needs to show every component, every wire run with its gauge/section clearly labeled, every fuse with its rating, and the polarity of every connection. Start from the battery positive terminal and work outward: main fuse → bus bar → fuse block → individual circuits. Then add the charging sources: solar MPPT, DC-DC charger, shore power charger — each with their own fused connections to the battery.
⚡ Expert tip
Photograph or scan your final diagram and laminate a copy that lives in the van — taped inside a cabinet door near the fuse box. Future-you (or anyone helping debug your system) will need it. I also keep a digital copy in my phone's notes app.
Example calculation for your setup
Results based on a typical use case
| Appliance | Power | Usage/day | Wh/day |
|---|---|---|---|
| Compression fridge | 45W | 24h | 1080 |
| LED lighting | 20W | 4h | 80 |
| Water pump | 30W | 0.5h | 15 |
| Phone charging | 15W | 2h | 30 |
| Daily consumption | 1205 Wh | ||
Daily consumption
1205 Wh
4.2A average hours
recommended section
1.5 mm²
For a 3m cable at 12V with this current, use
Adjust these values with the calculator below
VANPOWERCALC PROYOUR ENERGY PROFILE
YOUR ENERGY PROFILE.
This document contains the sizing of your future electrical installation, calculated based on your appliances.
Minimum Daily Consumption
0 WH / DAY
Inventory:
SYSTEM SIZINGPage 2
Battery
To guarantee 0WH without damaging your bank (80% max discharge):
0 AH
LiFePO4 12V
Solar
Minimum power required to recharge your consumption:
0 W
via MPPT
220V AC
Maximum power (with 25% safety margin).
0 W
No Need
Safety & CablingPage 3
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
SCHÉMA ÉLECTRIQUE
PANNEAUX SOLAIRES
0W
REGULATEUR MPPT
BATTERIE AUXILIAIRE
0 Ah
Lithium LiFePO4
FUSIBLE
FUSIBLE
BOÎTE À FUSIBLES 12V
Pompe, Leds, Frigo...
CONVERTISSEUR 220V
NON REQUI
PRO GEARPage 4
SHOPPING LIST
Where to find this equipment? Here is the community-approved selection.
12V 6-way Fuse Box
Mandatory protection
Digital Multimeter
Test your connections
Heavy Duty Crimping Tool
For perfect lugs
Heat Shrink Tubing
Insulation and safety
GENERATED BY VANPOWERCALC PRO - UNLIMITED.
About this tool
I draw my diagrams in three passes. First pass: block diagram showing major components and how they connect. Battery, solar, MPPT, DC-DC, fuse box, inverter — just boxes and lines. Second pass: add wire gauges calculated from the cable sizing calculator (amps × distance = required section). Third pass: add fuse ratings matched to wire gauges, not appliance draws. This is where most people mess up. Your 5A fridge on 2.5mm² wire gets a 20A fuse (protecting the wire), not a 5A fuse. The fridge has its own internal fuse. Color coding matters too: red for positive, black for negative, and I use blue for solar and orange for any 230V AC. When you're head-down in a cabinet at midnight, colors save you from connecting things backwards.
Frequently asked questions
What software should I use to draw a van wiring diagram?▼
Draw.io (free, browser-based) handles 90% of van diagrams. For more detail, KiCad is free and professional-grade but overkill for most van builds. Honestly? Pencil and grid paper works fine. The diagram doesn't need to be pretty — it needs to be accurate and readable.
What must be included in a van wiring diagram?▼
Every component, every wire with its gauge/section labeled, every fuse with its amp rating, and polarity markings (+ and -). Include wire colors if you're using color coding. Mark cable lengths for wire sizing reference. Label which circuits go to which fuse box positions.
How do I determine wire sizes for my diagram?▼
Use the voltage drop formula: Section (mm²) = (2 × Length × Current) / (57 × max voltage drop). For 12V systems, aim for less than 3% voltage drop. A wire sizing calculator makes this instant — enter amps and distance, get the required gauge.
Should the inverter be on the fuse box?▼
No. The inverter draws too much current for a blade fuse block (100-200A for a 2000W unit). Wire it directly to the battery bus bar through its own ANL fuse. The inverter's AC output then goes to a separate AC distribution with its own RCD and breakers.
Do I need a separate diagram for the AC side?▼
Yes, keep 12V DC and 230V/120V AC on separate diagrams — or at minimum in clearly separated sections with different colors. AC wiring has different safety requirements (RCD, earth bonding, conduit) and mixing the two on one messy diagram leads to dangerous mistakes.