Reference

DC Wire Gauge Chart: AWG, Amps & Fuse Sizes

To pick a DC wire gauge, you need two numbers: the current the wire will carry in amps, and the one-way length of the run. Find both in the sizing chart below and read off the smallest gauge that keeps voltage drop at or under 3%. The surprise for most first-time builders is how thick the wire has to be. A 12V system carries a lot of current for not much power, and high current over a long run sheds voltage as heat, so a modest load can still call for heavy cable.

Prefer to skip the tables? The interactive Wire Size Calculator does this math for you. Type in your amps, your run length, and 12V, 24V, or 48V, and it returns the gauge, the exact voltage drop, and the fuse size. The charts below use the same formula and the same copper resistance values, so the two always agree.

Table 1: AWG ampacity and fuse size

Ampacity is the current a wire can carry continuously without overheating. The numbers depend on the insulation rating and on how the wire is run. Two figures matter for off-grid work. The single-conductor column is a wire in open air. The bundled column is the conservative real-world value when wires run together in a loom, sheath, or conduit, which is how most of a van or cabin is actually wired. Use the bundled column unless you know the run is in free air, and remember that heat and tight bundles only pull these lower.

Basis: single-conductor values are ABYC E-11 for 105°C-rated copper, outside engine spaces. Bundled values are deliberately conservative, at roughly ABYC's derating for four or more conductors in a bundle (0.5 to 0.6 of free air), and are the same conservative numbers the wire-size calculator uses. The suggested fuse is a starting point that protects the wire and leaves headroom below its rating. Higher temperatures, more conductors in a bundle, and lower-rated insulation all reduce ampacity.

Table 2: Wire gauge by amps and run length (12V, 3% drop)

This is the table you will reach for most. It is sized by voltage drop, which is usually what forces 12V wire to be thick, long before ampacity does. Find your current down the left side, find your one-way run length across the top, and read the minimum gauge where they meet. Every value keeps round-trip voltage drop at or under 3% of 12V.

Basis: copper, round-trip drop = (2 × one-way feet × ohms-per-1000ft × amps) ÷ 1000, kept at or under 0.36V (3% of 12V). Resistance values are for solid copper; fine-stranded marine cable of the same gauge runs slightly higher resistance, so when a cell sits near its limit, size up one gauge for marine wire. "Parallel" means the run wants doubled cable or a higher system voltage. On the highest-current, shortest cells, also check Table 1: if ampacity calls for a thicker wire than voltage drop does, use the thicker one. * These two cells clear the 3% voltage-drop test but exceed their bundled ampacity in Table 1 (65A for 6 AWG, 85A for 4 AWG); run them in free air or size up.

Table 3: Fuse and breaker sizing by component

Fuses protect wire from a short or overload. The rule of thumb is to size the fuse at about 125% of the continuous load, round up to a standard fuse value, and confirm that value sits at or below the ampacity of the wire it is protecting. These are conservative starting points. Your charge controller, DC-DC charger, and inverter manuals will often name an exact fuse, and ABYC has the final word.

Three worked examples

The tables above answer the question in isolation. Real builds are where the two tables argue with each other, and knowing which one wins is most of the skill. Here are three runs from an ordinary van or cabin, worked end to end with the same numbers the tables use, so you can follow the reasoning rather than just trust the answer.

Example 1: a 12V compressor fridge, 15 feet away

A 12V fridge draws about 5A while the compressor runs, and it sits 15 feet of cable path from the fuse block. In Table 2, the 5A row meets the 15 ft column at 12 AWG. Check that against Table 1: 12 AWG carries 25A bundled, far more than 5A, so ampacity is not the constraint here and voltage drop is what set the gauge. Running the numbers, (2 × 15 ft × 1.588 ohms per 1000 ft × 5A) ÷ 1000 gives 0.24V of drop, about 2.0%, comfortably inside the 0.36V budget.

For the fuse, Table 3 puts a fridge at 15A to allow for compressor startup. That is well above 125% of the 5A running draw, and it sits below 12 AWG's 20A typical fuse and its 25A bundled ampacity, so the fuse still protects the wire. 12 AWG on a 15A fuse. If the fridge's own manual names a fuse, use that instead: a 5A running draw tells you what the wire must carry, not what the appliance is rated to be protected by.

Example 2: a 30A MPPT charge controller, 5 feet from the battery

This is the one that catches people out. Table 2 says the 30A row at 5 ft is 10 AWG, and the arithmetic agrees: (2 × 5 × 0.9989 × 30) ÷ 1000 is 0.30V, or 2.5% drop. Inside budget. So 10 AWG, done?

Not necessarily. Size the fuse next, and notice that the fuse you pick changes the answer. A 30A continuous output wants at least 125% of 30A, which is 37.5A, and the usual move is to round up to a standard 40A. But 10 AWG's bundled ampacity in Table 1 is only 35A. A 40A fuse on 10 AWG would let the wire run past its rating without ever blowing, which is precisely the failure a fuse exists to prevent. So if you fuse at 40A, the wire has to go up with it: 8 AWG, 50A bundled, 40A typical fuse, and a better drop at 0.19V.

The honest version is that choosing the 40A fuse decided the gauge, not the voltage drop. Victron, for example, allows 35A to 40A on a 100/30, and a 35A fuse would keep 10 AWG legal, with less margin for a hot day or a tight bundle. Check what your own controller's manual specifies before you pick either one. The transferable rule is the pairing: the fuse must never be rated above the ampacity of the wire it protects, under the conditions that wire is actually installed in.

Example 3: the battery cable to a 2000W inverter, 3 feet

A 2000W inverter at 12V pulls close to 200A continuous once sag and conversion losses are counted, not the 167A you get from dividing 2000 by 12. Over a 3 ft run, 2/0 AWG drops just 0.09V, so voltage drop is irrelevant at this length. Ampacity decides everything: 2/0 carries 330A as a single conductor in free air, but only 175A bundled, which is under the 200A load. That is why an inverter cable must be run in open air rather than buried in a loom with everything else. If your build genuinely cannot give it open air, do not shrug and bundle it anyway: step up to 4/0, which Table 1 rates at 230A even bundled, and which clears the load with margin.

Fuse it at 250A, which is 125% of 200A, mounted as a Class-T as close to the battery as it will go. If you noticed that Table 1 lists a 150A typical fuse for 2/0 and wondered why this says 250A, that is the two conditions talking: Table 1's fuse column is sized to the conservative bundled ampacity, while a short inverter cable in free air is working against the 330A column. Same wire, different install, different correct fuse. The mistake to avoid is the reverse of the one people expect: applying this 250A recommendation to a cable that is actually bundled, and therefore only rated 175A.

Treat 2/0 and 250A as the shape of the answer, not the answer for your inverter. Real 2000W units vary, roughly 200A to 240A of input current and 250A to 300A of fusing depending on the model's efficiency and low-voltage cutoff, and the manual is the authority. If it names a minimum gauge or a fuse value, that number wins over this page.

Get the right parts

Sized from the examples above. Wire is a commodity, so these are filtered searches rather than a single pick. What matters is that it is fine-stranded pure copper with marine-grade insulation, never copper-clad aluminium, and that the fuse goes in at the same time as the cable rather than later.

Why does 12V need such thick wire?

It comes down to one equation: current equals power divided by voltage. Run a 600W load at 12V and the wire carries 50A. Run that same 600W at 48V and it carries only 12.5A. The watts are identical, but the lower-voltage circuit pushes four times the current through the wire.

Current is what heats a wire and what drains voltage along a run, and both effects scale with how many amps are flowing. So a 12V system fights two problems at once. It needs thicker wire to carry the high current safely, and it needs thicker wire again to keep voltage drop in check over distance. That is why a simple 12V fridge run across a van can ask for cable that looks oversized to a newcomer. It is not overkill. It is the physics of low voltage.

How to read this chart

Work in three steps. First, find your amps. If you only know watts, divide by the system voltage: a 360W panel array on 12V is about 30A. Second, measure the one-way run, meaning the distance from the source to the load along the real cable path, not straight-line. Third, in Table 2 find where your amps row meets your length column and read the gauge.

Then sanity-check against Table 1. The voltage-drop chart gives the minimum gauge for clean power, but on short, very high-current runs the ampacity limit can be the stricter of the two. Whichever table demands the thicker wire is the one to follow. When a run sits right on the line, size up. Copper is cheap compared with tearing a finished build apart.

Where to put fuses

Every positive wire that leaves the battery gets a fuse or breaker, and it goes as close to the battery as you can manage. The reason is simple: the job of the fuse is to protect the wire from the battery's enormous short-circuit current. If the fuse sits far down the run, the unprotected stretch between the battery and the fuse can still catch fire in a fault.

Size each fuse to protect the wire it feeds, not the device on the end. A main fuse or Class-T fuse guards the big cable to the inverter and main bus. Smaller branch fuses in a fuse block guard each circuit. Negative and ground wires are not fused. If you take one rule from this page, take this one: no positive run without a fuse.

Stranded vs solid, and pure copper vs CCA

For off-grid power, use fine-stranded pure copper with marine-grade insulation. Stranding lets the cable flex and survive constant vibration in a van, RV, or boat. Solid wire work-hardens and eventually cracks where it moves, and its stiff insulation is not built for damp, mobile environments.

Avoid copper-clad aluminum, sold as CCA, for any power run. It is aluminum with a thin copper coating, so it has higher resistance than the same gauge of pure copper, runs hotter, and is weaker at terminals. The ampacity and voltage-drop numbers in these tables assume real copper. CCA does not meet them. The few dollars you save are not worth the fire risk, and CCA is not ABYC-compliant for marine work. Buy pure copper and crimp it with the right lugs.

Keep building

• Wire Size Calculator, the interactive version of these charts.
• How to wire a campervan electrical system, the full wiring walkthrough.
• 12V vs 24V vs 48V, why voltage choice changes everything downstream.
• Inverters, the biggest current draw in most systems.
• Batteries, where every positive cable starts and where the fuse goes.
• Appliance power consumption, for the amps to bring to Table 2 when you only know watts.
• Off-grid glossary, if ampacity, derating, or Class-T are new words.

Frequently Asked Questions

What gauge wire for a 2000W inverter at 12V?

A 2000W inverter on a 12V battery pulls close to 200A continuous once real-world voltage sag and conversion losses are counted (2000W at about 90 percent efficiency and 11.5V under load works out to 195 to 205A), and more on startup. The 167A you get from dividing 2000 by 12 is the lossless textbook number; size for the real draw. For the short cable from the battery to the inverter, use 2/0 AWG for runs under about three feet and 4/0 AWG for longer runs, run in free air rather than inside a loom. That free-air condition is what Table 1's single-conductor column assumes. Pair it with a 250A fuse or breaker mounted close to the battery. Always check the inverter manual, since some makers spell out a minimum gauge.

How do I size a DC fuse?

The fuse protects the wire, not the device. Pick a fuse that is at least 125% of the continuous load so it does not nuisance-trip, then round up to a standard fuse value, and make sure that value is at or below the wire's ampacity. Mount it as close to the battery as you can on every positive run. When in doubt, follow ABYC guidance and the device manual.

Why is voltage drop a problem at 12V?

Power is volts times amps, so a 12V system carries far more current than a 24V or 48V system for the same load. More current over the same wire means more voltage lost as heat along the run. Lose too much and lights dim, pumps run weak, and charge controllers misread the battery. Keeping drop at or under 3% on important lines is the usual target, which is why 12V wire ends up so thick.

Can I use household wire for 12V?

It is a poor choice. Solid romex is stiff, not rated for vibration, and its insulation is not built for the damp, moving environment of a van or boat. Use fine-stranded copper with marine-grade insulation instead. It flexes, resists corrosion, and handles the constant motion that would work-harden and crack solid wire over time.

What size wire from battery to inverter?

Match the wire to the inverter's continuous current, not its watt rating. At 12V a 1000W inverter wants 4 to 2 AWG, and a 2000W inverter wants 2/0 to 4/0 AWG. Keep the run as short as you can, fuse it near the battery, and use the inverter manual's stated minimum if it gives one. At 24V or 48V the same inverter draws far less current and needs much thinner cable.