Get the correct cable size, fuse rating, and fuse type for any DC wiring run — with real-world installation derating applied. Designed for van builders, RV owners, boat builders, and off-grid installers.
Answer a few plain-English questions about your device and installation. We'll calculate the correct cable size, voltage drop, and fuse rating — and explain what it all means.
to pull components from your saved build
What this tool covers
Inverters & Inverter-Chargers
Watts → amps conversion, bidirectional cable notes
MPPT Solar Chargers
Charge current, battery-side cable sizing
DC-DC Chargers
Output cable + alternator input cable
Winches & High-Draw
Intermittent vs continuous, surge current
Marine Circuits
ABYC E-11, bilge pumps, bow thrusters, tinned cable
Any DC Circuit
Enter amps directly for any other DC load
Installation derating
A cable bundled with others can only carry 70% of its rated current. We apply the correct derating factor for your installation method automatically.
Voltage drop
Every cable has resistance. Over a long run, this causes voltage to drop — your device receives less than the battery provides. We calculate this and flag if it's too high.
Fuse sizing
The fuse protects the cable — not the device. We recommend the correct fuse size and type for your current level and battery chemistry.
Undersized cables are a fire risk
An undersized DC cable doesn't just perform poorly — it can overheat and start a fire. DC fires in vehicles and boats are notoriously difficult to extinguish. This tool helps you get the sizing right, but always have high-current wiring checked by a qualified auto-electrician or marine electrician before use.
How these numbers are calculated
Cable ampacity ratings are based on AS/NZS 3008.1 and IEC 60228 for single-core copper conductors at 30°C ambient. Installation method derating factors are derived from AS/NZS 3008.1 Table 22 and IEC 60364-5-52. Fuse sizing follows the 125% continuous current rule per AS/NZS 3000. Voltage drop is calculated using V = I × R over the full circuit length.
Important disclaimer
These results are a guide only based on standard electrical engineering principles. They are not a substitute for advice from a qualified auto-electrician, marine electrician, or licensed electrical contractor. Factors specific to your installation — including ambient temperature, cable routing, bundling, local wiring regulations, and the specific characteristics of your equipment — may require different sizing. High-current DC wiring carries a real risk of fire if incorrectly sized or installed. Always have your wiring checked by a qualified professional before use.
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