How to Install a 110-Volt 20-Amp Circuit Breaker


A 20-amp circuit breaker requires a wire that is larger than the normal 15-amp circuit breaker wire used in most houses. For a 20-amp breaker, use No.12 AWG wire or larger. They are usually a little larger in diameter than the No.14 AWG wire. The 20-amp circuit breaker can serve up to 2400 watts. It is great for small to medium air conditioning units or electric heaters. No.10 AWG is strongly recommended but not required.

Things You'll Need

  • Insulated screwdriver
  • Gloves
  • 20-amp circuit breaker
  • Marker
  • No.12 or No.10 AWG electric wire
  • Flashlight
  • Turn off power to the main breaker.

  • Open the service panel door, then check the panel for an empty spot to install the new 20-amp breaker. The circuit breaker should be the type and size recommended by the service panel's manufacturer. Not all circuit breakers fit in all panels. If you are not sure what kind to buy, jot down the name and size of an existing breaker and buy the same kind. The only difference with the new breaker is that it will be rated for 20 amps.

  • Mark the empty spot you found on the service panel cover with a marker. Remove the screws holding the service panel. There are usually four screws, one in each corner. The screws are holding the panel cover and door all together.

  • Find an empty terminal screw on the neutral bar. Strip about an 1/8 of an inch of insulation off the white wire and insert the wire in the terminal. Tighten the screw and pull gently on the wire to make sure that it's snug.

  • Insert the black wire into the terminal screw on the circuit breaker. Strip about 1/2 an inch of insulation off the wire and insert the wire into the terminal screw on the breaker. Tighten the screw and gently pull on the black wire to make sure it's secured to the breaker.

  • Insert the circuit breaker into the hot bar. Align the breaker to the empty spot on the service panel. Hold the breaker at a 45-degree angle and insert the breaker into the small security niche. Push the breaker back until it is secured to the "hot" bus bar. The hot bus bar has a small piece of metal that fits in an opening on the circuit breaker. Align the opening exactly with the hot bus bar metal piece, then push firmly until it's snugly in place.

  • Insert the green wire into the ground bar. Grounding the circuit is very important in case of an electric fault. Find an empty terminal screw on the ground bar, insert the green wire into it, then tighten the screw. Make sure you keep all the wires neat inside the panel.

  • Remove the circuit breaker's metal cover on the service panel cover. Each circuit breaker has a small cover aligned horizontally on the panel's inner cover. This cover should be removed before the service panel cover is reinstalled.

  • Put the panel cover back in place, then attach the corner screws. Turn the circuit breaker on to test the new 20-amp circuit breaker.

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  • "Wiring: Step-by-Step Projects"; Fran J. Donegan; 2004
  • Photo Credit electrician image by Greg Pickens from
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