Electricity can be dangerous so it's essential you take care when wiring electrical items, particularly if they use high voltage to operate, such as your home electricity supply. Electricity is measured in voltage, amperes and ohms. However, it is the amperes that are the most dangerous, as this is the current draw or energy that travels through the wires from the power source to the electrical appliance. If you're wiring an electrical appliance, it's important you calculate the correct wire to use based upon the amperes the appliance draws.
Things You'll Need
 Tape measure
 Pen
 Paper
 Calculator

Measure the distance between your appliance and the place the power comes from. For example, if the wire from the appliance is going to plug into an electrical socket in your home use a tape measure to work out the length between the power socket and the appliance and round it up to the nearest foot.

Multiply the result by 2. For example, if the distance is 5 feet then multiply 5 by 2 to get 10 feet. Write down the result using a pen and paper.

Look at the label on the electrical device you intend to wire to find out the amperes it requires. Write the amperes on a sheet of paper. If the device only provides wattage, then divide the wattage by 110 to get the amperes. Wattage is amperes multiplied by voltage and your home electricity supply is 110 volts. For example, if the wattage is 2,000 then divide 2,000 by 110 to get 18 amperes.

Use your computer and connect to the internet. Enter the weblink in the resources section.

Look at the table displayed on the webpage. Refer to your sheet of paper to find the nearest corresponding distance from the green column on the left hand side of the table.

Look across the table, left to right and look at the yellow top row from the table that is titled "Current (amps)." Refer to your sheet of paper and find the nearest corresponding amperes.

Look down and across, so the "Length" line meets the "amps" column. The figure in the box is the AWG wire size you need for your electrical device.
References
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