Two Rules, Not One
1. Ampacity (safety): the wire must carry the circuit’s current without overheating. This is what the fuse/breaker protects — size the fuse to the wire, not the load.
Owner guide
12V DC Wire Ampacity & Voltage-Drop Chart (ABYC E-11)
In low-voltage DC systems, voltage drop — not fire-safety ampacity — is usually what actually governs wire size. This chart covers both.
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Field notes
In low-voltage DC systems, voltage drop — not fire-safety ampacity — is usually what actually governs wire size. This chart covers both. Applies to vans, truck campers, trailers, fifth wheels, motorhomes, and skoolies alike; the physics don’t change with the chassis. 1. Ampacity (safety): the wire must carry the circuit’s current without overheating. This is what the fuse/breaker protects — size the fuse to the wire, not the load.
Ampacity by Wire Gauge (Free Air, Copper)
Ampacity figures are free-air baseline values consistent with NEC Table 310.16 practice, adapted for RV low-voltage wiring.
Minimum Wire Gauge by Distance & Load (3% Drop — Critical Circuits)
Round-trip (loop) length in feet. Use this table for battery charging, inverter feeds, and main panel runs.
The Fuse Protects the Wire, Not the Device
A common and dangerous mistake: sizing the fuse to the appliance’s rated draw instead of the wire’s ampacity.
Related Reference Pages
Battery Charging Voltage Chart Battery & Charging Systems Guide Van Build Electrical Planning Full Field Guide
Owner checklist
- Ampacity (safety): the wire must carry the circuit’s current without overheating. This is what the fuse/breaker protects — size the fuse to the wire, not the load. A 10 AWG wire rated for 30A gets a fuse of 30A or less, regardless of what’s actually plugged in.
- Voltage drop (performance): even a wire that’s technically “big enough” for the amperage can drop so much voltage over distance that chargers misbehave, lights dim, and inverters fault. Per ABYC E-11, size critical circuits (battery charging, inverter feeds, main panel runs) for
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Pricing teaser
Trip fee $75 within 30 miles, then $1.50/mi. Labor ~$150/hr (1-hour minimum, billed in 30-minute increments). Diagnostic $175 applied toward repair if you proceed.
Active corridor: Montana · Wyoming · Idaho · Washington — case-by-case beyond. Credentials (text): Victron Professional Certified Installer · weBoost Authorized Installer · Peplink Certified Associate · Dometic Professional Certified.