How to Calculate Power Cable Size

Every electrical appliance must be safely connected to a power supply. The cable must be capable of carrying all the power needed by the appliance and of coping with the heat generated as electricity flows through the wires. Calculating the size of your power cable necessitates knowing the voltage of the power supply and the power rating of your appliances. Most households in the United States have a 120-volt supply. A straight forward mathematical formula tells you the power rating, or size, of the cable.

Things You'll Need

  • Calculator


    • 1

      Determine the wattage of each appliance to be attached to the power cable. Each appliance has a label showing its power consumption in amps, watts or kilowatts.

    • 2

      Calculate the power rating of the cable, in amps, by using this formula: amps = watts/volts. For example, a 120-volt supply and a total of 2 kilowatts of appliances attached to the cable indicates that the minimum cable size will be (2,000/120) amps, or 16.67 amps.

    • 3

      Check your calculations for errors. Divide the amp rating by the voltage, and the answer should be the wattage of the appliances you expect to run from the cable. If it isn't, there was an error in your calculations.

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  • Photo Credit Monkey Business Images Ltd/Valueline/Getty Images

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