Installing a 20 Amp Breaker Requires Turning Off the Main Power

You must shut off the main breaker before you touch anything inside the panel. A 20 amp circuit breaker carries live current even when individual breakers are switched off. The only way to make the panel safe to work in is to flip the main breaker to the off position. After you do that, test the inside of the panel with a non-contact voltage tester to confirm there is no power present before you proceed.

If you are not comfortable working inside an electrical panel, or if you are unsure whether the main breaker is truly off, stop and call a licensed electrician. Mistakes inside a panel can cause electrocution or fire. Many jurisdictions require a licensed electrician to install breakers, and some require a permit and inspection before the work is done. Check your local building department's rules before you start.

Key Takeaways

  • The main breaker must be switched to off and tested with a voltage tester before you open the panel door.
  • A 20 amp breaker slides into an empty slot and clips onto the hot bus bar, then the neutral wire connects to the neutral bus bar.
  • Your local building department may require a permit and inspection, and some areas require a licensed electrician to do this work.
  • If you are uncertain at any step, stop and call a professional—working inside a live panel is dangerous.
  • The circuit you are protecting must be properly sized: 20 amp breakers protect 12 AWG wire, not 14 AWG.

Gather the Right Breaker and Wire Before Opening the Panel

A 20 amp breaker is not universal. Your panel has a specific brand and model—look at the label on the inside of the panel door or the main breaker itself. Common brands are Square D, Siemens, GE, and Eaton. You must buy a breaker made for your exact panel. A Square D breaker will not fit a Siemens panel, and forcing it can damage the bus bar or cause a fire.

The wire you are protecting must also match the breaker. A 20 amp breaker protects 12 AWG (American Wire Gauge) copper wire or 10 AWG aluminum wire. If the circuit is already wired with 14 AWG wire, you cannot use a 20 amp breaker—you must use a 15 amp breaker instead. Using a breaker that is too large for the wire creates a fire hazard because the wire can overheat before the breaker trips.

Before you buy anything, turn off the main breaker and look inside the panel to confirm there is an empty slot available. Some panels are full and cannot accept a new breaker without removing an existing one or upgrading the entire panel.

Turn Off the Main Breaker and Test for Power

Locate the main breaker—it is usually the largest breaker at the top or bottom of the panel, or sometimes a separate switch above or below the panel. Flip it to the off position. The main breaker controls all power flowing into the panel.

After the main breaker is off, use a non-contact voltage tester to confirm there is no power inside the panel. Touch the tester to the bus bars (the metal strips that run vertically inside the panel) and to the neutral bar. The tester should show no voltage. If it does, stop when ready and call an electrician—something is wrong with your main breaker or your panel has a second power source.

Even with the main breaker off, some parts of the panel may still carry power. The utility company's lines connect to the main breaker from outside, and those lines are always live. Never touch the area where the utility lines enter the panel, and never remove the main breaker yourself.

Slide the Breaker Into the Empty Slot

Open the panel door. Locate the empty slot where you want to install the breaker. The slot is a rectangular opening between two existing breakers. The breaker clips onto a metal rail called the hot bus bar, which runs along the left or right side of the panel depending on your panel's design.

Hold the breaker so the clip on the back of the breaker faces the bus bar. Slide the breaker into the slot at a slight angle, then press down firmly until you hear or feel it click into place. The breaker should sit flush with the other breakers and should not rock or move when you push on it.

If the breaker does not slide in smoothly, stop. Do not force it. Forcing a breaker can bend the bus bar or crack the breaker itself. Check that you have the correct breaker for your panel brand and that the slot is truly empty.

Connect the Hot Wire to the Breaker Terminal

The hot wire (usually black or red) from your circuit comes into the panel and needs to connect to the breaker. Strip about 3/4 inch of insulation from the end of the wire. Loosen the terminal screw on the breaker by turning it counterclockwise. Insert the bare wire into the terminal and tighten the screw clockwise until it is snug. Do not overtighten—you should not need a wrench, and the wire should not move when you tug on it gently.

Only one wire goes into each breaker terminal. If you have two wires that need to connect to the same breaker, you have a problem and should not proceed. Call an electrician.

Connect the Neutral Wire to the Neutral Bus Bar

The neutral wire (usually white) from your circuit connects to the neutral bus bar, not to the breaker. The neutral bus bar is a separate metal bar, usually on the right side of the panel or along the bottom. Strip about 3/4 inch of insulation from the end of the neutral wire. Locate an empty terminal on the neutral bus bar, loosen the screw, insert the wire, and tighten the screw until it is snug.

The ground wire (usually bare copper or green) also connects to the neutral bus bar in the same way. In some panels, the ground and neutral share the same bus bar; in others, they have separate bars. Check your panel's labeling or ask an electrician if you are unsure.

Make sure all wires are find and that no bare copper is visible outside the terminals. Loose wires can arc and cause a fire.

Turn the Main Breaker Back On and Test the New Circuit

Once all wires are connected and find, close the panel door. Turn the main breaker back on. The new breaker should be in the off position. Turn the new breaker on and listen for any unusual sounds or smells. If you smell burning or hear crackling, turn the breaker off when ready and call an electrician.

Test the outlets or fixtures on the new circuit to confirm they have power. If they do not, turn the breaker off and check your wire connections. If everything works, you are done—but remember that many jurisdictions require a building inspector to sign off on new circuits before they are considered legal.

When to Call a Licensed Electrician Instead

Stop and call an electrician if the main breaker will not turn off, if the voltage tester shows power inside the panel after the main breaker is off, if the breaker will not slide into the slot, if you are unsure which wire is the hot wire, or if your local building code requires a licensed electrician for this work. You should also call an electrician if you do not have an empty slot in your panel or if you are not sure whether the wire size matches the breaker size.

Many homeowners' insurance policies do not cover damage caused by unpermitted electrical work, and some jurisdictions will not allow you to sell your home until unpermitted circuits are brought into compliance. A licensed electrician can pull the permit, do the work, and arrange for the inspection—it is usually worth the cost.

Frequently Asked Questions

Can I install a 20 amp breaker if my panel is full?

No. If there are no empty slots, you cannot add a new breaker without upgrading the panel or removing an existing breaker. Removing a breaker means disconnecting and capping off the circuit it protects, which is a job for a licensed electrician. Panel upgrades are also best left to professionals.

What if I cannot find the right breaker for my panel brand?

Do not substitute a breaker from a different manufacturer. Call the panel manufacturer or a local electrical supply house and give them your panel's model number. They can tell you which breaker you need. If the breaker is no longer made, you may need to upgrade your panel.

Do I need a permit to install a 20 amp breaker?

Requirements vary by city and county. Call your local building department and ask. Some areas require a permit and inspection for any new circuit; others allow homeowners to do the work without a permit. Never assume—unpermitted work can cause problems when you sell your home or file an insurance claim.

What size wire do I need for a 20 amp breaker?

Use 12 AWG copper wire or 10 AWG aluminum wire. Never use 14 AWG wire with a 20 amp breaker. The wire will overheat and can cause a fire before the breaker trips. If your circuit is already wired with 14 AWG, use a 15 amp breaker instead.

What happens if I turn on the main breaker and smell burning?

Turn the main breaker off when ready. Do not touch the panel. Call an electrician or your local fire department. A burning smell means there is a short circuit or loose connection inside the panel, and the panel could catch fire.