How to Determine If an Extension Cord Can Handle a Load

To operate safely and efficiently, electrical tools and appliances must be connected to an extension cord that supplies adequate power.

Match extension cord capabilites to the items that plug into them.Match extension cord capabilites to the items that plug into them.
Overloading an extension cord can lead to tool failure and power outages. Breakers may become faulty, which, in extreme cases, can lead to a fire in the breaker box. The amount of power that a tool or appliance uses should always match or be less than the load that the extension cord is designed to handle.

Determine the amperage of a tool that will run on the extension cord by checking the tool plate. Each tool has a metal plate showing the serial number, the model number and the amperage.

Determine the amperage of tools that list the power specification in watts and volts by writing down the wattage shown on the tool plate. Divide the wattage by the voltage to obtain the amperage. For example, if the plate indicates that a tool uses 360 watts and is 18 volt, the amperage of the tool is 360 divided by 18, or 20 amps.

Write down the amperage for each tool.

Add the amperage of each tool to get the total number of amps that will run on the extension cord.

Check the paper safety tag on the extension cord for the maximum amperage that is safe for the cord. If the cord will not handle the total amperage from the tools, use a cord with a higher safety rating.

Things You Will Need

  • Pen and paper
  • Calculator


  • Determine the size of extension cord for one tool or appliance by comparing the amperage on the metal plate with the extension cord tag.


  • Overloading an electrical cord can lead to tools being shorted out and appliance motors failing.
  • Use outdoor-approved extension cords for use outside. Outdoor cords have a thicker outer coating around the electrical wires to protect them from dragging over or being but by objects. Household extension cords are for light-duty indoor applications only.