What wire gauge to use for 12V distribution in our radio station, or for mobile use? Choosing the right cable gauge is not a minor detail: it is essential to ensure the system operates efficiently and safely. A cable that is too thin can cause voltage drops, load malfunctions, or, in the worst cases, overheating and fire hazards.

On the other hand, a properly sized conductor ensures that the current required by the load arrives without significant losses, reducing internal resistance, minimizing voltage drop, and keeping the voltage stable at the load. This is especially important when dealing with long cable runs.

For this reason — rather than relying on generic “rules of thumb” — it is good practice to calculate the wire gauge based on current, cable length (considering round trip) and allowable voltage drop. This approach ensures a sizing that is consistent with the actual needs of the system and with relevant technical standards.

I have prepared this quick calculator, designed specifically for our purposes.

Simply enter:

• The maximum current — which is the sum of the maximum currents of the devices to be powered by that run
• The linear length of the run — the calculator already accounts for the round trip
• The nominal voltage — preset to 13.8V
• The allowable voltage drop percentage — preset to 3%

to get the recommended gauge, chosen from commercially available sizes larger than the calculated result.

The formula used is

S = (2 × ρ × L × I) / ΔV

where

S = cross-section in mm²
ρ = 0.0175 Ω·mm²/m (copper at 20°C)
L = one-way length in meters
I = current in amperes (A)
ΔV = maximum voltage drop in volts