How to Figure What Size Wire for an Electrical Service


The electrical service panel is the panel that receives the power from the power lines and distributes it into the building or home. The power line wire is selected and installed by the power company. You are responsible for selecting and installing the electrical lines that distribute the power into the building or home. The wire size you use will vary depending on the voltage and the amperage entering the structure.

Things You'll Need

  • Screwdriver
  • Ammeter
  • Remove the service panel cover. Remove the circuit breaker cover to view the wiring. Use a screwdriver to remove the screws holding the cover.

  • Use the ammeter to measure the amps and volts entering the house. Insert the ammeter into the two screws that hold the wires from the power line. Be very careful as the power line wires have electricity at all times. Most homes in the United States will have 240 volts but in some rural areas it can be 120 volts.

  • Call the local building department and ask them what are the required wire size for the voltage and amperage your house is receiving. The laws vary by county so you will have to call them to ensure the wiring will pass inspection. In most counties it will be either one or two gauge wire.

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