Calculating what Size Electrical Cable to Use

by DoItYourself Staff

When it comes to deciding what size electrical cable you should use, there is one important aspect to keep in mind: the smaller the wire gauge is, the larger the ampacity the wire can handle. Wire ampacity is the amount of electrical current the wire can safely handle without causing a fire or overheating the cable. Thus, the two are inversely related. As the wattage needs increase, the gauge of the wire decreases.

Large Scale Pump Applications

However, if you are looking to wire a large scale pump application, you are going to need to be more precise. In order to calculate the size you will need, you will need to know the amps needed to power it, the distance from the outlet to the device, and if you are using copper or aluminum wires. With this information, plug it into this formula that is based on Ohm’s Law.

Single Pump Formula

Wire size = (conductor resistivity)(2)(amps)(one way distance in feet)
Conductor resistivity is 11.2 for copper wire and 17.4 for aluminum wire, at 127 degrees F (53 degrees C)