How to install a transformer for doorbell

Modern doorbell transformers step down 120 volts of electricity to between 12 volts and 24 volts. The transformer regulates the voltage that actually reaches the doorbell chimes. Knowing this, you'll find that 16-volt transformer installation is no different than any other doorbell installation. The transformer voltage output, however, must match the doorbell chime voltage requirement for the unit to work correctly. If you're retrofitting a 16-volt transformer into a doorbell chime circuit, say in a real estate application when the transformer has burned out, make sure that the chime does, in fact, require 16 volts before installation begins.

1. 1.

   Locate the junction box where the original transformer was located. Flip the circuit breaker and turn off the power to the junction box.

2. 2.

   Remove the junction box cover with a screwdriver. Test the wire connections inside with a voltage tester. If there is still voltage, turn off the main breaker. Test again.

3. 3.

   Remove the old transformer, if applicable. Unscrew the wire nuts that attached the old wires in the junction box. Pull the wires out.

   Unscrew the doorbell wires on the front of the transformer. Pull them away. Then unscrew the locknut holding the transformer in place on the junction box. Use a needle-nose pliers.

   If there was no transformer to begin with, pop out one of the side knockouts. They are easily bent inward with a screwdriver, then grasped with a needle-nose pliers, bent back and forth, until they snap out.

4. 4.

   Mount the transformer into the knockout hole. Screw on the locknut from the inside and tighten it down with the pliers.

5. 5.

   Attach the black transformer wire to the black feed wire in the box. Strip the wire with a wire strippers until about a 1/2 inch of bare wire shows. Use a wire nut to secure the wires together. Repeat this process with the white wire.

6. 6.

   Attach the doorbell wires to the front screws on the transformer. The hot wire is the lead wire from the button, and the neutral wire is the lead wire from the chime. A red screw on the transformer denotes where the hot wire will be attached. Any other colored screw denotes where the neutral wire will be attached. Screw them down firmly.

   Lee has over two decades of hands-on experience remodeling, fixing, and improving homes, and has been providing home improvement advice for over 13 years.

   Learn more about The Spruce's Editorial Process

   Updated on 07/05/22

   Reviewed by

   Larry Campbell

   
   

   Reviewed by Larry Campbell

   Larry Campbell is an electrical contractor with 36 years of experience in residential and light commercial electrical wiring. He worked as an electronic technician and later an engineer for the IBM Corp. is a member of The Spruce Home Improvement Review Board.

   Learn more about The Spruce's Review Board

   
   

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   Project Overview

   • Total Time: 1 - 3 hrs
   • Skill Level: Intermediate
   • Estimated Cost: $25 to $50

   Your home's doorbell is the official greeter for everyone who stops by your house. So, if you want the doorbell to be as dependable and solid as possible, a wired doorbell (in contrast to a wireless doorbell) is a good choice.

   Wired doorbells never need their batteries changed. Because they use household 120V electricity stepped down to a 16-volt operating current via a transformer, they're able to deliver a strong current to the chimes for a ring that's easy to hear. Plus, if you'd like a doorbell that's lit and easy to see even in the dark, this feature is available with wired doorbells.

   A wired doorbell is a perfect—and permanent—complement to a house.

   Before You Begin

   If you are replacing a wired doorbell, keep the existing wire in place when you remove the button. In many cases, the wire should still be in good shape for reuse. More importantly, reusing the doorbell wire eliminates the need to fish new wire through the walls.

   Purchase the four major wired doorbell components separately—button, wire, transformer, and base—or purchase a kit that includes everything that you need. Note that one advantage of buying a wired doorbell kit is that you can be confident that all of the materials are compatible.

   How Wired Doorbells Work

   The main elements of a wired doorbell system work in conjunction, a process that starts when a visitor presses the doorbell button.

   Doorbell Button

   The wired doorbell button is located to the left or right of the front door.

   Behind the doorbell button is a hole. Two separate strands of doorbell wire feed through the hole and are attached to the back of the doorbell button at two terminals. One wire leads to the doorbell transformer and the other wire leads to the doorbell base (chimes).

   Doorbell Wire

   The doorbell wire, or bell wire, is thin, 20/2 coated copper wire. It has two strands, often with one strand coated in white plastic and the other strand is coated in red plastic. The strands are separated into single strands for this project.

   Doorbell Transformer

   The doorbell transformer is a solid-state electrical device that attaches to the side of an electrical box.

   The transformer converts the higher 120V household current input to a lower 16V output that's usable by the doorbell system. The doorbell system cannot use 120V household current directly; it needs to be reduced or stepped down to a lower voltage.

   Two electrical terminals are located on the back of the transformer. One doorbell wire from the doorbell button leads to the transformer. A separate wire leads from the transformer to the doorbell base.

   Doorbell Base or Chimes

   The doorbell base contains the chimes. On back are three terminals, often in this order:

   • REAR: REAR refers to a back doorbell. This terminal leads to an optional second doorbell at the back of the house. As this project is about wiring a front doorbell only, ignore this terminal. It will not be used.
   • TRANS: TRANS means "transformer." A single strand bell wire leads from this terminal to the doorbell transformer.
   • FRONT: FRONT refers to the front doorbell. A single strand bell wire leads from this terminal to one of the terminals on back of the doorbell button.

   Electrical Box

   The electrical box is a metal, enclosed box that has a 120V electric cable running into it. The box might be dedicated solely to powering the doorbell transformer or it might have another device such as an outlet running from it (though these other devices need to be mounted on separate boxes).

   The box should have available knockouts that can be opened up to allow the transformer to be attached.

   Safety Considerations

   Exercise caution when wiring the transformer to the electrical box, since the box contains household current sufficient to cause injury or death. Work on the electrical box only when the circuit breaker to the box has been shut off. Use a non-contact voltage tester to make sure that power is off before working on electrical wires.

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   What You'll Need

   Equipment / Tools

   • Cordless drill
   • Drill bits and drivers
   • Flathead screwdriver
   • Phillips head screwdriver
   • Wire stripper
   • Pliers
   • Voltage tester

   Materials

   • Doorbell button
   • 50 feet 20/2 coated copper wire
   • Doorbell transformer
   • Doorbell base (chimes)
   • Plastic wire connectors

   Instructions

   1. Plan Layout

      • Doorbell: Install the doorbell next to the front door. The button should be around 42 to 56 inches high.
      • Transformer: Install the transformer against an available electrical box. Often, doorbell transformers are located near the electric service panel.
      • Doorbell Base: Install the doorbell base in a central location where the chimes will be heard in all parts of the house. The base will be surface-mounted.

   2. Install Transformer

      With the electricity turned off at the service panel, knock out one of the protective covers from a hole on the side of the electrical box.

      Attach the transformer to this hole by feeding the three wires in first, followed by the threaded section of the transformer. Turn the locknut on the inside of the electrical box to tighten the transformer to the box.

      Tip

      Remove a knockout in a metal electrical box by tapping it firmly with a screwdriver until it loosens. When one side of the knockout is free, twist it several times by hand or with the pliers to fully detach the rest of the knockout.

   3. Wire Transformer to Electrical Box

      Attach the three transformer wires to the three 12- or 14-gauge wires that are already in the box. Attach the white wire to the white wire; black wire to the black wire; and green wire to either the green or bare copper wire. Twist the wires clockwise and follow by capping them with plastic wire connectors.

      Screw the faceplate or device with cover back onto the electrical box.

   4. Attach Doorbell Base Wire to Transformer

      Screw a single strand of bell wire onto either of the two terminals on the back of the transformer.

   5. Run Wire From Transformer to Doorbell Base

      Fish the single strand of bell wire from the transformer to the location of the doorbell base.

   6. Attach Transformer Wire to Doorbell Base

      Attach the wire from the transformer to the TRANS terminal on the back of the doorbell base.

   7. Run Transformer Wire to Doorbell Button

      Attach a second wire to the back of the transformer on its remaining terminal. Fish this wire to the location of the doorbell button.

   8. Attach Transformer Wire to Doorbell Button

      Attach the wire from the transformer to either of the two terminals on the back of the doorbell button.

   9. Attach Wire From Doorbell Base to Doorbell Button

      Attach a single strand of bell wire on the back of the doorbell base onto the FRONT terminal. Fish this strand to the doorbell location.

   10. Attach Doorbell Base Wire to Doorbell Button

       Fish the doorbell base wire to the location of the doorbell. Attach it to the remaining terminal on the back of the doorbell.

       With both wires attached to the back of the base, mount the base on the wall. Attach the decorative face by snapping it into place.

   11. Mount Doorbell Button

       With the cordless drill, first drill two pilot holes for the doorbell button. Next, turn the two included screws clockwise to mount the button to the doorframe.

   Doorbell Wiring Map Summary

   FromToTransformer, either terminalDoorbell button, either terminalTransformer, either terminalBase, TRANS terminalBase, FRONT terminalDoorbell button, either terminalBase, REAR terminalDo not use. Not applicable for front door-only installationsEach connection uses one single-strand 20-gauge wire (or as indicated with your transformer)

   Troubleshooting: Wired Doorbell Does Not Sound

   Check Doorbell Button

   The problem might be with the button itself. Depressing the button may not properly close the electrical circuit. Remove the doorbell button. Detach the wires from the button.

   Holding the coated section of the wires, touch the bare ends together. If the doorbell rings, the button is at fault. Replace the button with a new one.

   Check Doorbell Base

   Remove the cover from the base. Make sure that the wires are attached to the terminals and are secure. With a multimeter, determine whether electricity is flowing through the wires.

   Alternatively, remove the TRANS wire and touch it to the FRONT terminal while a helper pushes the doorbell button. Hold only the coated sections of the wire. You should see a small spark if electricity is properly flowing.

   When to Call a Professional

   Attaching the doorbell transformer to an existing electrical box and wiring it can be done by most do-it-yourselfers with basic electrical skills. Since the box contains full household current, though, you may feel more comfortable with hiring a qualified, licensed electrician to make this connection.

   If there is not an available electrical box, an electrician can install one for you by feeding off of a nearby power source or by running a new circuit from the electric service panel.

   Related Topics

   • Electrical Problems & Repairs

   Article Sources

   The Spruce uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

   Do you need an electrician to replace a doorbell transformer?

   While replacing the transformer can be a DIY project if you have experience working on similar repairs, you may want to call an electrician for this fix. The doorbell transformer is generally mounted on an electrical junction box or wall studs in a hidden area, or near the main breaker box.

   Where do you put a doorbell transformer?

   In many houses, the doorbell transformer is installed in a junction box behind the internal doorbell chime or mounted near other electrical components in a basement or crawlspace.

   Does it matter which wire goes where on a doorbell transformer?

   Secure the connection with electrical tape. Connect the two doorbell wires to the two screw terminals. Typically, it does not matter which wire goes to which terminal. Turn the power back on at the breaker.