How to Find and Test a Doorbell Transformer

Many builders will install the doorbell transformer near the main electrical panel or inside the doorbell’s chime or bell enclosure for easy access. Read further on how to find a doorbell transformer in your house.  

• Check the garage: The doorbell transformer can be found near outlet boxes where cable TV lines and telephone cables are installed. They are commonly placed there because communications and cable TV lines are also low voltage and are often grouped together.
• Check around the security alarm system: Some builders tie the doorbell wiring directly into the security system. The doorbell transformer may be located on the wall near your security alarm keypad or control station.
• Look in the utility room: A lot of doorbell transformers are installed in the utility rooms of your home’s HVAC unit or furnace. It may be tucked away at the bottom of the HVAC junction box or mounted on the ceiling of the room. One reason for the transformer to be installed here is it could be surface mounted to the wiring of the existing HVAC or furnace junction box.
• Try the attic: Doorbell transformers are sometimes installed on an existing junction box in the attic of a ranch or a house with an attached garage near the front door.
• It may be in the closet: The doorbell transformer may be attached to the wall opposite the closet door. Move a few coats around and it might be there.
• Check under the stairwell: If you live in a two-story house and there is a storage closet beneath the stairs, the doorbell transformer may be wired there. Try looking on a wall under the stairs leading to the basement.

Knowing how to test a doorbell transformer means you can pinpoint why your doorbell is not ringing or chiming and make the repairs to get it working again. 

Test the wiring to determine if it is the source of your doorbell’s failure. Make sure it’s properly connected before you run any voltage test. The following steps show you how to check for problems in the wiring. 

• Cut the power by switching off the main breaker in your home.
• Doorbell wire is usually 18-gauge and should be free of splices, tears and corrosion.
• If the wire in your transformer appears worn or damaged, you’ll need to replace it.

Your doorbell transformer may not be producing enough voltage for your doorbell to work or to meet the power supply requirements of a smart doorbell or video doorbell. The following takes you through the steps of testing the voltage.   

• Using a voltage tester or voltage meter, test the doorbell transformer by setting the meter to 25VAC (volts alternating current).
• Measure the voltage on the transformer to see if it’s producing enough electricity. Touch each probe to each screw head. The voltage should be at or around 16.
• If the voltage is too low, replace the transformer to repair your doorbell unit.