How to Wire a Lighting Transformer

Updated February 21, 2017

Low-voltage lighting uses halogen lamps to provide bright and efficient lighting for your home, both indoors and outdoors. The systems operate on 12 volts, and therefore need a transformer to lower the voltage from the standard 120 volts in your wall socket. Many kits come with all the hardware and instructions you need to install them. However, if you have a used transformer with no instructions, you need enough electrical skill to select various parts and do basic wiring and connections to layout your lighting system without specific instructions.

Identify the input and output connections on your transformer. Usually, a low-voltage lighting transformer will have a cord with a plug on the 120-volt input side. The output side will have any of a variety of types of connectors, some of which may not even need tools to make the connections. Larger transformers may have two or more outputs to branch off in different directions. The input may be marked "120 volts" and the output marked "12 volts."

Connect your lighting system to the 12-volt output of your transformer. Select a wire size compatible with your system, and use connecting hardware compatible with your wire size and the particular hardware of your transformer output. Each branch of your lighting system will have two connections.

Plug your transformer into a wall socket. If your transformer does not have a cord already attached, you will need to make one. Use a two-conductor wire for a two prong wall plug or a three-conductor wire for a three-prong plug. Your transformer could require either.


Low-voltage lighting systems produces a far lesser risk of electric shock around water, including pools, spas and ponds.


For lighting systems outdoors or indoors in places that have water--such as kitchens or bathrooms--only plug your transformer into a ground fault circuit interrupter (GFCI) outlet. If you don't have one available, replace an existing socket or have an electrician wire in a new one. Don't exceed the output rating of your transformer. Count up the wattage rating of all the bulbs in your system. Your transformer wattage rating should equal or exceed the total. Transformers can be rated "indoor," "outdoor" or "indoor/outdoor." Never install a transformer outside of its rated location.

Things You'll Need

  • Various electrical wire and hardware
  • Basic electrician's tools
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About the Author

Richard Asmus was a writer and producer of television commercials in Phoenix, Arizona, and now is retired in Peru. After founding a small telecommunications engineering corporation and visiting 37 countries, Asmus studied broadcasting at Arizona State University and earned his Master of Fine Arts at Brooklyn College in New York.