A low-voltage transformer powers an electric doorbell, with a voltage that is typically 10 to 16 volts. The transformer voltage must match the label on the doorbell. If you are replacing an old doorbell, you will probably need to replace the transformer as well. Most of the wiring is low-voltage and is safe to work with. However, the transformer connects to a 120-volt outlet. If you are not comfortable working with electricity, you should have the work done by an electrical contractor.
Find a suitable place to mount the transformer. Most homes have an existing doorbell. The transformer is usually in the garage or basement. Look for a transformer mounted to the front of an electrical box about 6 feet off the ground.
Turn off the main breaker. If there is an existing transformer, remove the cover plate and the wires inside the box that connect to the transformer. If there is no existing transformer, you need to find a suitable outlet box. You can find one in the garage or in a hallway.
Attach the new transformer to the mounting plate. Strip the wires and attach them to the electrical wires in the box. Connect one of the transformer wires to the black wire and the other wire to the white wire. If there is a green or bare wire, attach it to the electrical box with a sheet-metal screw. Wrap the wire around the screw and tighten securely.
Mount the transformer to the electrical box. Make sure the wires are securely inside the box. Attach a bell wire to each of the two terminals on the front of the transformer. Use the existing wires if you are replacing the doorbell.
Run the wires along the wall to a suitable location for the doorbell. Use the insulated staples to attach the bell wires to the wall. Again, if there is an existing doorbell, remove the old unit and replace it with the new one. Mount the doorbell in a location that will allow you to hear the bell in all areas of the house.
Attach one of the bell wires to the doorbell. Wrap the wire around the terminal and tighten the screw. If the doorbell has more than two terminals, connect the wire to the terminals marked "front." Some doorbells have a different tone for the back door. If this is the case, the bell would have a separate set of terminals marked "back."
Run two wires from the doorbell to the doorbell button located near the front door. Connect both wires to the doorbell button and secure the button to the wall.
Connect one of the two bell wires at the doorbell to the second "front" terminal. Twist the two remaining wires together and secure them with a wire-nut. Tuck the wire inside the bell housing. Turn on the main breaker.
You can turn the main breaker back on as soon as you wire and mount the transformer to the electrical box. The low voltage from the bell wire is safe to work on. If you are updating an old doorbell, replace the transformer and the doorbell and reconnect the bell wires.