The wire gauge depends on the current (amps) and cable length. For example, a 10A load at 3 meters needs at least 2.5mm² (14 AWG) wire to keep voltage drop under 3%. Use the calculator above to find the exact size for your setup.

For 12V DC systems, a maximum voltage drop of 3% (0.36V) is the industry standard recommendation. Critical electronics may require less than 1%, while lighting circuits can tolerate up to 5%. The calculator defaults to 3% but lets you adjust this in advanced settings.

Common conversions: 16 AWG = 1.5mm², 14 AWG = 2.5mm², 12 AWG = 4.0mm², 10 AWG = 6.0mm², 8 AWG = 10.0mm², 6 AWG = 16.0mm², 4 AWG = 25.0mm². The calculator shows both units simultaneously so you always have both values.

Yes. In a DC circuit, current flows through both the positive and negative conductors. The total cable length for voltage drop calculation is twice the one-way distance. The calculator handles this automatically with the round-trip option enabled by default.

The fuse should be rated at 125% of the continuous load current, then rounded up to the nearest standard fuse size. The fuse must always be smaller than the wire ampacity rating. For example, a 10A continuous load needs a 15A fuse with at least 2.5mm² wire.

Always place the fuse as close to the power source (battery positive terminal) as possible. The fuse protects the wire from overheating in case of a short circuit -- it does not protect the load device. Each positive wire leaving the battery should have its own appropriately sized fuse.

Yes. Copper resistance increases with temperature, which means more voltage drop and power loss in hot environments. At 40°C, resistance is about 8% higher than at 20°C. Use the advanced settings in the calculator to account for your expected ambient temperature.

To calculate the correct fuse size for a 12V circuit: First, determine the load current in amps (divide watts by 12V). Then multiply by 1.25 to get the 125% safety margin. Finally, round up to the next standard fuse size. For example, a 60W load draws 5A, so you need at least a 7.5A fuse. The fuse rating must never exceed the wire ampacity.

14 gauge wire (1.5mm²) is rated for up to 15 amps continuous. Use a fuse rated at or below 15A -- typically a 10A or 15A blade fuse depending on your actual load. Never install a fuse larger than the wire can safely carry.

12 gauge wire (4.0mm²) is rated for up to 25 amps continuous. A 20A or 25A fuse is appropriate. Choose the fuse based on your actual load current (125% of load, rounded up), making sure it does not exceed the 25A wire rating.

The fuse should be placed as close to the battery positive terminal as possible -- ideally within 18cm (7 inches). The wire between the battery and the fuse is unprotected. If that unprotected wire shorts against the chassis, there is nothing to prevent a fire. This is the most important fuse placement rule in any DC system.

Fuses are sized by their amperage (current) rating -- the maximum continuous current they can carry before melting. Common types: blade fuses (ATC/ATO) up to 30A, MAXI blade fuses up to 60A, ANL bolt-down fuses up to 200A, and Class T fuses up to 400A. Always match the fuse to the wire gauge, not the load device.

The main battery fuse should be sized based on the total maximum load of all circuits combined. For a typical camper or boat with 100-200A total capacity, a 150-200A ANL or Class T fuse is common. Each individual circuit leaving the fuse box also needs its own smaller fuse matched to its wire gauge.