If you are wiring your home, it may be necessary to remove a knockout from an electrical panel to install a breaker. Knockout panels are the elevated quarter-size circles stamped on the sides to allow installation of breakers. These circles protect spaces on the panel not in use. It is easy to remove the knockouts by following these tips.

Prepare to Work

For this project, you need:

  • work gloves
  • hammer
  • needle-nose pliers
  • flat-blade screwdriver
  • file
  • cable connector

Be aware electrical knockouts can have sharp edges, so wear gloves. Shut off the main power supply to the house from the breaker box. 

Ensure no current exists by running a multimeter over the breaker box. If it doesn't beep, no current exists. If you get a beep, wait several minutes, and run the multimeter again.

Figure Proper Size

Use a screwdriver to detach the screws on the panel cover, and set the cover and hardware aside. Check for available space in the breaker panel. A knockout will look like an empty space.

Determine the size opening you need for the cable or conduit diameter. Measure the size of each knockout, and add 3/8 inch to get the right size. For example, the actual size of an opening for a one-half inch diameter is seven-eighths of an inch. A three-fourth inch diameter equals one and one eighth inch opening.

Remove the Knockout

The knockout should have a slit. There will also be various sizes, so choose the one to fit the opening size you need. Insert a screwdriver blade in the slit, and hit it lightly with a hammer. Use enough force to dislodge the knockout.

Grasp the bent portion of the  knockout corner with needle-nose pliers, and twist the point back and forth to create fatigue. If you can't fit the pliers in the corner, tap a screwdriver in the slit as before, until you have enough space. 

Be aware of sharp edges and burs on the edges of the opening. If you find burrs or sharp edges, file them down until they are smooth to prevent wires from being cut. 

Detach the locknut from the connector with pliers, and slide it into the space outside the box. Cable connectors protect wires from damage. Give the locknut a spin to secure. Insert a screwdriver in the valley of the locknut, and tap it with a hammer or pliers.

Reinstall the cover of the breaker box, and restore power. Test the new installation. If you don't trust your skill, or the breaker doesn't work, contact an electrician.