Caution: Turn off power to a working fixture’s circuit by removing the fuse or turning off the circuit breaker. Check that the power is off by turning on the controlling switch; the fixture should not light.
Remove the old fixture by loosening fasteners and wires. Unscrew the lid from the new fluorescent fixture and use a screwdriver to punch out the center tab on the back of the channel. If the old mounting box has a threaded stud pointing down, add a hickey and a threaded nipple to it. If there is no stud, use a locknut to fasten a nipple to- a horizontal strap; then screw the strap to the box.
Feed the fixture’s wires through the punched-out hole and the nipple; then connect them to the ceiling wires with wire connectors-black wire to black, white to white, grounding wire to grounding wire. Fit the punchedout hole over the nipple, push the channel to the ceiling, and secure it with a washer and locknut.
A heavy fixture with two or more lamps often has a large hole in the low center of the channel to accommodate an eight-sided ceiling box. Add a reducing nut and nipple to the stud in the ceiling box; feed the fixture wires through the cutout and connect them to the ceiling wires as above. Place the cutout hole over the nipple; then thread a strap to the nipple and secure it with a locknut.
Install a circular fluorescent fixture the same way: add a reducing nut and nipple to the ceiling-box stud, connect the fixture wires to the house wires, and fit the wires into the box. Place the center hole of the fixture over the nipple and secure it with a cap nut.