How To Wire a Doorbell Transformer

Updated: Jul. 06, 2023

Yes, you can wire your doorbell yourself! Let us take the mystery out of wiring a doorbell transformer with this step-by-step guide.

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1-4 hours






Modern doorbells are wireless, smart and even provide video. But many models currently in homes, even some of today's popular smart doorbells, are wired. So don't be intimidated if you need to wire a doorbell transformer. You can do this!

Whether you're replacing an old doorbell or adding a new one, wiring the transformer itself is the same. One side has black, white and green wires for the line voltage and ground, and the other side has terminals to allow low-voltage wires to feed your doorbell. Doorbells can't handle the power coming from your electrical panel, so the voltage must be lowered, usually between 8V and 24V. That's what the transformer does.

If you are replacing an old doorbell transformer, start with Step 1. If you are adding a new one, follow the directions on your new kit to add the doorbell and route the power wires and low-voltage bell wires to the transformer location. Then follow the steps for wiring the new transformer below.

Here's how to wire a doorbell transformer.

Tools Required

  • Lineman's pliers
  • Non-contact voltage tester
  • Screwdriver
  • Wire strippers

Materials Required

  • Doorbell transformer
  • Wire nuts

Project step-by-step (7)

Step 1

Find the transformer

  • Locate the doorbell transformer, if replacing.
    • The transformer may be in the garage or utility room, near the doorbell chime or in the attic.

Doorbell MaterialsAlly Childress for Family Handyman

Step 2

Turn off the power

  • Turn off the breaker that controls the doorbell.
  • If you don’t know which breaker it is, turn off one breaker at a time and test the 120V power coming into the box by holding a non-contact voltage tester to the cable until you find the right one.

  • Remove the cover housing the 120V wiring powering the doorbell.
  • Test all wires in the box and turn off any additional breakers, or the main power.

Box Extender Turn Off Or On BreakerAlly Childress for Family Handyman

Step 3

Remove transformer

  • Separate line (120V) wires from the old transformer by snipping them with wire strippers near the wire nut.
    • Snip the hot, then neutral, then ground.
  • Snip the low-voltage doorbell wires leaving the transformer terminals.
  • Unscrew the transformer mounting screw, or use pliers to remove the locknut holding it to the box.
  • Remove the transformer.

Doorbell Wire Low VoltageAlly Childress for Family Handyman

Step 4

Replace or add the transformer

  • Feed the line side wires (black, white, green) on the transformer into the box.
  • Tighten the mounting screw or locknut to secure transformer to box.

Doorbell Wire Low Voltage 2Ally Childress for Family Handyman

Step 5

Wire the transformer (doorbell wires)

  • Strip 3/4-inch of insulation from the low-voltage wires going to the doorbell.
  • Make a hook in the end of each wire.
  • Attach one wire to each of two screw terminals, wrapping the wire clockwise around the screw.
    • If you have three terminals, consult your doorbell instructions to see which two you should use.
    • It doesn’t matter which wire goes on which of the two terminals.
  • Tighten screw terminals with a screwdriver.

Doorbell Attach Transformer To BoxAlly Childress for Family Handyman

Step 6

Wire the transformer (line wires)

  • Strip 1/2-inch of insulation from the black, white and green wires.
  • Splice the ground wires from the power, the transformer and the electrical box (if metal) together.

    • If you have a metal box but no wire present to ground it, add a grounding pigtail by screwing the green grounding screw attached to the pigtail into the metal box’s screw terminal.
  • Splice the two neutral (white) wires, then splice the hot (black) wires.

Doorbell Feed Line Through BoxAlly Childress for Family Handyman

Step 7


  • Tug on all wire connections to make sure they’re secure.
  • Close up the electrical box housing the 120V transformer connections.
  • Turn on the breaker.
  • Test the doorbell.

Doorbell Closeup Of Transformer ConnectionsAlly ChildressAlly Childress for Family Handyman for Family Handyman