This wire gauge calculator uses the length and current.
The process is as follows:
- Using load_current and length, we first find the wire gauge that meets the selected voltage_drop.
- We find a wire gauge for which the ampacity is higher than the fuse size (fuse size per owner’s manual, otherwise we compute it as follows: fuse_size = load_current x 1.4).
- We compare 1. and 2. above and keep the wire with the largest gauge.
- and there you are!
Main factors to consider:
Wires can carry a certain amount of current continuously and no more; more current means the wire will overheat (and melt) as it cannot dissipate the heat that is generated by too much current flow. That characteristic is called AMPACITY (maximum current that a wire can carry continuously without exceeding its temperature rating). Certain factors reduce the ampacity rating of wires and the voltage drop as well:
AMBIENT TEMPERATURE OF 50°C (122F) OR MORE
A wire located in ambient temperature of 50°C (122F) or more loses its ability to dissipate heat, and, therefore, its ampacity is reduced by 15%. (note: this is per ABYC standards "In Engine Room"). This is most likely the case for a wire running in the wall/ceiling of a van because temperature in there is much higher than in the living space (that's especially true for darker painted vehicles).
LOAD RUNS CONTINUOUSLY FOR 20 MINUTES OR MORE
A wire that carries a current flow for a long duration (~20 minutes) builds up more heat. As the temperature of a wire increases, so does the resistance to current flow = more voltage drop. To mitigate this factor, the load current is increased by 25% for the voltage drop calculation (but not for the fuse/breaker size calculation). This is not an ABYC requirement at the moment; however, it is generally accepted by marine product manufacturers (such as Blue Sea)
WIRE IN CONDUIT, INSULATION, OR BUNDLED WITH 2 (OR MORE) WIRES
A wire located in a conduit, sheath, running through insulation, or bundled with 2 (or more) wires loses its ability to dissipate heat, and therefore, its ampacity is reduced by 30%. This is not an ABYC requirement at the moment; however, it is generally accepted by marine product manufacturers (such as Blue Sea).
WIRE IN CONDUIT, INSULATION, OR BUNDLED WITH 2 (OR MORE) WIRES
A wire located in a conduit, sheath, running through insulation, or bundled with 2 (or more) wires loses its ability to dissipate heat, and therefore, its ampacity is reduced by 30%. This is not an ABYC requirement at the moment; however, it is generally accepted by marine product manufacturers (such as Blue Sea).