Safety Disclaimer

This page is the one that every safety notice on the site links back to, so it is worth reading properly rather than skimming. It sets out what the guidance here is, what it is not, and where the real hazard in a 12V vehicle build actually sits. It is not a legal formality dressed up as advice. The hazard is genuine and it is specific.

What is the actual danger in a 12V system?

Not electrocution. Twelve volts will not push a meaningful current through dry skin, and this is the reason people are relaxed about 12V in a way they never are about mains voltage. That relaxation is the problem, because the hazard in a vehicle house battery is not voltage at all. It is available current, and it is enormous.

A single 100Ah LiFePO4 pack will deliver several hundred amps into a short circuit without complaint, limited mainly by its own battery management system and by the resistance of whatever is shorting it. A 400Ah bank of four such packs in parallel can deliver several thousand amps for the fraction of a second it takes to vaporise metal. That energy has to go somewhere, and it goes into whatever has resistance: a loose terminal, an undersized conductor, a poorly crimped lug, a chafed cable rubbing on a body seam, or a spanner laid across two battery posts.

The failure is thermal rather than electrical. Insulation melts, the conductor arcs, and the fire starts in a sealed vehicle compartment, frequently in a space people are sleeping in. This is not a hypothetical: undersized and unfused DC cable is one of the most common causes of fire in owner-built vehicle electrical systems, and it is entirely preventable with correct sizing and correct fusing.

The three rules this site will not soften

Every electrical page here repeats these, and the repetition is deliberate.

1. Every circuit is fused at the source of power. That means within a few inches of the battery terminal or the busbar the conductor leaves from, at or below the ampacity of the smallest conductor it protects. The fuse exists to protect the cable against a fault anywhere along its length, including six inches from the battery post, so a fuse at the far end protects nothing. There are no exceptions for short runs, temporary runs, or the one you intend to redo properly later.
2. The fuse protects the wire, never the appliance. If an appliance needs protection beyond that, it has its own internal fuse. Choosing a fuse to match an appliance rating rather than the conductor rating is how people end up with a 30A fuse protecting 16 AWG wire rated at 25A, at which point the wire is the fuse.
3. Cable is sized by two tests and must pass both. Ampacity is a safety limit set by how hot the insulation is allowed to get. Voltage drop is a performance limit set by the length of the run. On any run longer than a few feet, voltage drop usually governs and the conductor ends up larger than ampacity alone would allow.

On top of those, one instruction that is not arithmetic: have any lithium installation inspected by a qualified installer before it carries load. Not because the arithmetic on this site is unreliable, but because an installation has a hundred details that no calculation covers, and because a second set of eyes on a system that lives in a vehicle you sleep in is worth the money every single time.

What does OverlandSetup claim, and what does it not?

What it claims: that the arithmetic is correct and checkable, that the sources are named, and that where a figure could not be confirmed it is left blank rather than invented.

Electrical figures follow ABYC E-11, the standard most low voltage vehicle and marine installations are held to. Ampacity uses the 105C copper column for conductors outside engine spaces with three or fewer current-carrying conductors bundled together, and every page that could involve an engine space states that those figures derate by roughly 30 percent there. Voltage drop uses the standard two-way formula, with the factor of two included because current travels out and back. Worked examples show their steps so you can check them rather than trust them.

What it does not claim: that any of this is an electrical certification, a professional design, or a substitute for the standard itself. It is not, and it never will be. Specifically:

• Nothing here has inspected your vehicle. Existing wiring, alternator type, chassis grounding quality, compartment ventilation, ambient temperature and the way a particular vehicle is used all change the right answer, and none of them are visible from here.
• Nothing here replaces a manufacturer installation manual. Where a component manual disagrees with a figure on this site, the manual wins. It was written by the people who built the thing.
• We do not test gear in person and never say we do. Every specification quoted is the manufacturer published figure, cross-checked against retailer listings and verified owner reviews where those disagree. Any site claiming hands-on testing of forty power stations is telling you a story.
• No page here is a legal, tax, insurance or regulatory opinion. Vehicle modification rules, roadworthiness requirements and grey water disposal rules vary by jurisdiction and change, and checking yours is your responsibility.

Why payload and GVWR figures need special care

Every payload, GVWR, gross axle weight rating and roof load figure on this site is an example or a typical range, offered so you can see the shape of the problem. None of them applies to your vehicle.

The authoritative figure is the sticker on your driver door jamb, which is specific to your vehicle as built. The same model can differ by several hundred pounds depending on drivetrain, cab configuration, trim level and factory options, so a brochure figure or a number from a forum is not a substitute. Roof load is a separate and stricter limit with two values, static and dynamic, and the dynamic figure is the one that constrains a build. Gross axle weight rating applies to each axle individually, and an overland load can put a vehicle over its rear axle rating while it is still under GVWR overall.

The only figure that tells you the truth is a weighbridge ticket for the finished vehicle, loaded exactly as you travel, with everyone aboard. Every estimate here and every estimate in your spreadsheet is a guess until that prints. The payload calculator and the payload and GVWR guide both say so on the page.

How current are the prices and specifications?

Prices were accurate when each page was compiled and change constantly, which every page carrying a price says in the page itself. Build totals in particular are the sum of prices captured at one moment, and they are published because seeing what a complete system costs is more useful than seeing what one component costs, not because the total will still be exact next month. Confirm every price on the listing before you order.

Specifications are the manufacturer published figures at the time of writing. Makers revise cycle ratings, charge times and weights between hardware revisions and firmware versions, several quote charge time at an input wattage they do not print next to it, and a few quote cycle life to 70 percent capacity while their competitors quote it to 80. Where a figure could not be confirmed against the maker own documentation, the field is left blank and the row is dropped rather than filled with a plausible number. On a site whose readers are about to spend several thousand dollars on a vehicle electrical system, a precise-looking invention is worse than a visible gap.

The statement in full

A 12V system is low voltage but not low energy. Every circuit must be fused at the source of power, within a few inches of the battery terminal, at or below the ampacity of the smallest conductor it protects. Size cable for voltage drop as well as ampacity, torque every terminal to specification, and have any lithium installation inspected by a qualified installer before it carries load. Everything on this site is researched guidance, not an electrical certification and not a substitute for ABYC E-11 or your component manufacturer instructions.

That paragraph is rendered verbatim on every calculator and every page that touches wiring, fusing, charging or battery handling. It is deliberately not collapsed behind a details element and not set in small grey type at the foot of the page, because a safety statement that has to be hunted for is decoration rather than a warning.

If you find a mistake

Tell us. Use the contact page and include the page address, the figure you believe is wrong, and your working or the standard you are quoting. Corrections to ampacity, voltage drop and fuse sizing go ahead of everything else in the queue, because an error in those is a fire risk rather than merely an embarrassment. When a fix is published we say what changed rather than quietly editing the page, because a reader who built from the old figure deserves to know.

OverlandSetup.com is a small independent site. It is funded by disclosed affiliate links, the terms of which are on the affiliate disclosure page, and no commission changes a ranking, a recommendation or a safety figure. The about page explains the method behind the pages, and the terms of service set out the legal position.

Where to go next

• 12V wiring and fusing guide, the page this disclaimer exists for
• Wire gauge calculator
• Fuse sizing chart
• About OverlandSetup, and where the figures come from
• Help and site information