How To Wire a Second Doorbell Chime

Understand a wired doorbell system

A wired doorbell system has three components: a low-voltage (15- to 20-volt) transformer, a chime and a doorbell button. They are connected by 18- or 20-gauge low-voltage wires.

• The transformer is the heart of the system. It can be plugged into a 120-volt receptacle or wired directly to the main electrical panel.
• The doorbell chime produces the ring. It may be round or square and is often hanging on a wall, although some people like to hide it in a closet.
• The doorbell activates the chime. It’s mounted on the trim next to the front door and is basically a push-button switch that closes the electric circuit and activates the chime when someone pushes the button.

Although it’s at low voltage, a doorbell circuit works like the receptacle circuits in the house. Just as you can add an extra receptacle by daisy-chaining it to an existing one, you can daisy-chain a new chime to the existing chime.

The only potential problem is that the existing transformer may not supply enough power for both chimes. If you have a 15V transformer, you should replace it with one that supplies 30 volts.

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Replace the transformer (if necessary)

Locate the transformer and check the voltage. If it’s between 10 and 16 volts, replace it with a bigger one.

1. Unplug the transformer or turn off the breaker in the panel that controls it.
2. If the transformer is hardwired, disconnect the wires from the screw terminals on the back of the device, using a screwdriver. Note which wire connects to the hot terminal (it should be black or red), which connects to the neutral terminal (it should be white) and which connects to the ground terminal (bare or green).
3. Install a new hardwired transformer by connecting the wires to the same terminals.

Note: If you have a plug -in transformer, you only have to plug it into a receptacle, but wait to do this until after you’ve finished all the wiring.

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Locate the existing chime

Cut power to the existing transformer if you don’t have to replace it. Locate the existing chime, which may be mounted on the wall or ceiling or possibly placed on an upper shelf in a closet. If you’re having trouble finding it, turn the power back on and have someone repeatedly press the doorbell while you follow the sound. Once you find, it, turn the power back on.

• Pro tip: The low voltage in a doorbell circuit isn’t dangerous, but you can still get an uncomfortable shock if you touch a live wire.

Run a cable to the new chime

Choose a location for the new chime. Run an 18- to 20-gauge solid low-voltage cable with two solid — not stranded — wires from the original chime to that location. Walker advises running the wire before connecting it to the original chime to ensure that you have the proper length of wire to connect the two.

Running wire to the new chime can be harder than it sounds. You may have to remove baseboards or crown moldings to put the wire behind them, or you may have to run the wire through the attic or basement.

Connect the new chime

At this point, Walker recommends placing the new chime box in the desired location and wiring it as directed in the instructions. The chime should come with an easy-to-follow wiring diagram, but here’s some clarification:

You should see three terminals, one marked “Front,” one marked “Rear” and one marked “Trans.” If you have only one doorbell, choose “Front” or “Rear,” depending on whether the doorbell is located at the front door or the back door. Connect the hot wire (black or red) to that terminal by wrapping it clockwise around the terminal screw and tightening the screw with a screwdriver.

Connect the return wire (usually white) to the “Trans” terminal in the same way. Walker cautions not to add any more wires to this chime than the wire that goes to the original one.

Connect the original chime

“Sister in the wires at the opposite end to your labeled wires on the original chime box so that they are the same setup as the second box,” instructs Walker. In other words, connect the hot wire to either the “Front” or “Rear” terminal, depending on which one is used, and the return wire to the trans terminal.

To make a connection, bend the end of the wire clockwise, loosen the terminal screw and hold the wire already on the terminal in place while you add the new wire and tighten the screw.

• Pro tip: If the original chime uses the “Front” terminal, use that terminal on the new chime. If you use the other one, the chime won’t work.

Test the chimes

“Turn the power breaker back on,” instructs Walker, “and test to see if the new setup works before attaching the chime boxes to the walls or ceilings. This way if there is a problem, you can troubleshoot without having to redo all the previous work.

• Pro tip: If you’ve wired everything correctly, and both chimes don’t sound when you push the doorbell, check the connections. It’s a common mistake to fail to tighten the screws sufficiently.

About the Expert

• Geoff Walker is the company Superintendent for ASAP Restoration in Phoenix, AZ. He has 50 years of hands-on experience in remodeling and restoration.