How to Replace Low Voltage Lighting Transformer
Sometimes when a light is not working it isn’t always the bulb.
Some recessed lights use a transformer that is mounted to the light above the ceiling. Low-voltage recessed lights use transformers to convert high-voltage electricity to a low-voltage power supply, usually 120V down to 24V or 12V. Replacement transformers must match the recessed light's old transformer's input and output voltage ratings. Placing standard voltage on a low-voltage light bulb causes its filament to burn up almost instantly.
If you have a remote transformer for low-voltage track lighting or low-voltage halogen lights you need to locate the enclosure where the transformer is installed and replace it with a matching one. These transformers can be susceptible to voltage spikes and surges caused by lightning strikes and power outages.
Always use caution when working with electricity.
1. Turn off the electricity to the recessed light at electrical panel by shutting off the circuit breaker that controls the lights. You may have to shut off the power to the entire room if the lighting is not on a separate circuit.
2. You may be able to access the light's electrical box from the attic, if possible, or from the room. Transformer access from below the ceiling requires removing the trim cover and light bulb and unscrewing the can from its mounting bracket with a screwdriver. Trim covers pull straight down and unsnap from the housing. The housing of the light, called a “can”, screws to a mounting bracket near the bottom, usually with a 1/4-inch hex-head screw. After unscrewing the can, push it up into the ceiling and turn the can until the electrical box can be seen through the hole in the ceiling.
Recessed Lighting Fixture with Transformer Mounted on Electrical Box
3. Open the recessed light's electrical box with a slotted screwdriver. Remove the wire connectors from the old transformer and the electrical wiring. Separate each set of wires. There are two high-voltage and two low-voltage wires. The two low-voltage wires go to the light socket and the two high-voltage wires enter the electrical box from above the ceiling.
4. Unscrew the transformer's mounting screws with a screwdriver or 1/4-inch nut driver. Remove the old transformer from the electrical box.
5. You may need to take the transformer to a home center or electrical supply house to match the ratings. They are common so there are usually in stock. The label on the transformer lists the ratings and shows the wiring guide. Pay special attention to the primary and secondary voltage ratings and the wattage. For track lighting systems you can overload undersized transformers if higher wattage bulbs are installed in the fixtures.
6. Note the new transformer's wiring guide. The wiring guide lists each wire, its insulation color and its function. Usually there is a black and white wire for the primary coil that is connected to the black and white wiring from the house. The low-voltage wires are red, blue, or yellow and are connected to the low-voltage wires going to the light.
7. Attach the new transformer to the recessed can light's electrical box with the screws that held the old transformer.
8. Connect the high-voltage wires from the transformer, labeled “Primary,” to the high-voltage wires that enter the box from above the ceiling and secure them with wire nuts. Often the transformer uses black and white colored insulation for the high-voltage wires. If so, then connect black to black and white to white. Otherwise, connect the transformer wire labeled "Hot" to the black wire and the transformer wire labeled "Neutral" or "Common" to the white wire.
9. Twist the transformer's low-voltage, labeled "Secondary," wires to the low-voltage wires that connect to the light socket and secure them with wire nuts. Many transformer manufacturers use blue and yellow insulation for the secondary wires. The low-voltage wires can be connected either way and do not have to be matched to the wires going to the light.
10. Replace the electrical box's cover. Screw the can to its mounting bracket, replace the light bulb and trim piece.
Note: Transformers may or may not have a green ground wire depending on the manufacturer.