When connecting 30 Amps electric breakers, generally, one uses relatively short wires, well shorter than 50 feet. Note: the actual surface temperatures due to the current flowing through the wires will be lower, but to keep calculations simpler, maximum allowed currents are calculated using these formulas - remember that the actual goal is to keep energy losses low in longer cables AND to keep their maximum surface temperatures at the certain level. Now, we have to check the required AWG value for given wire lengths, depending on the wire surface temperature - values are given in the following chart: Wire Length / Surface feet (37.5 Amps) When longer wires are used, in order to find the wire that can support 30 Amps current, the required Ampacity increases by 10% for every 50 feet (~15m) of the wire length.įor example, when calculating the required Ampacity for the 50 feet, 100 feet, and 150 feet wires, we can use (default value is 37.5 Amp, after applying the '80% Rule'):ĥ0 feet wire: Ampacity = 37.5 Amps * 1.1 = 41.25 Ampsġ00 feet wire: Ampacity = 37.5 Amps * 1.2 = 45 Ampsġ50 feet wire: Ampacity = 37.5 Amps * 1.3 = 48.75 Amps For the very long wires, one must also calculate energy losses due to the wire length. That means that we are not looking for a wire that features an Ampacity of 30 Amps, but for:Īnd if we check the Ampacity values in the chart, we get:Īs one can see, as soon as the 80% Rule is applied, actual wire thickness increases from AWG 10 (30 Amps) to AWG 8 (40 Amps) for 60☌/140☏.Īnd these values are only for relatively short wires. In order to increase safety and to keep the energy losses in check, the 80% Rule is applied.

Note: if we can't find the exact Ampacity for a certain wire at the required temperature, we must choose the next larger one.

When calculating the required wire thickness, it is necessary to apply a few additional rules in order to keep the wire surface temperatures at the maximum levels and to keep energy losses to the required minumum.įor example, if we check the default Ampacity values in the chart, we can find out the Ampacity of 30 Amps of the following wires: Note: Ampacities are given for enclosed wires ambient temperatures.

Wiring a 30 amp breaker