Step 1
Remove the Old Fixture and Inspect the Wiring
Remove the Fixture
Turn off the power to the light fixture at the main circuit panel. Remove the nut or screws securing the dome-shaped canopy and lower it. Then remove the screws securing the crossbar to the electrical box and lower the fixture.
Step 2
Make Sure the Power is Off
Test the wires to make sure the power is off. Move the tip of a non-contact voltage detector near each wire to make sure the power to all wires in the box is turned off (make sure the light switch is turned on). If the tester lights, switch off circuit breakers or loosen fuses one at a time until the tester light goes off. Disconnect the wires from the light fixture. Leave other wires connected and tucked into the electrical box.
It’s hard to believe, but many of the light fixtures now sold at home centers and lighting showrooms can’t be safely installed in most houses wired before 1985. These fixtures are clearly labeled with a warning that reads “For supply connections, use wire rated for at least 90 degrees C.” The reason is simple: Fixtures with this label generate enough heat to damage the insulation on older wires and cause a fire hazard. Wires manufactured after 1985 are required to have coverings that can withstand the higher temperature.
If you know your wiring was installed before 1985, don’t use fixtures requiring 90-degree–rated supply wires. To confirm that you have 90-degree–rated supply wire, look at the cable jacket or wire insulation. If you have plastic sheathed cable (often referred to as Romex), look for the letters NM-B or UF-B printed on the plastic sheath. If your wiring is fed through conduit, look on the wire insulation for the letters THHN or THWN-2. If you’re still unsure, either call an electrician or choose a fixture that isn’t labeled with a supply wire temperature requirement.
Check the Electrical Box for Capacity and Strength
Heavy Fixtures Require Strong Boxes
If you choose a heavy light fixture (the one we bought weighed in at a hefty 25 lbs.), check your electrical box to make sure it will support the weight. The National Electrical Code (NEC) allows you to hang up to 50 lbs. from any electrical box that is threaded to accept No. 8-32 machine screws for attaching the crossbar (see “Mounting with Screws and Cap Nuts” and “Mounting with a Threaded Pipe” in Additional Information below). This includes almost every type of ceiling box.
For practical purposes, make sure your electrical box is securely fastened to solid framing before you hang a new light fixture from it. If your light fixture weighs more than 50 lbs., it has to be supported independent of the electrical box. An easy solution is to install a fan brace box (available from home centers and hardware stores) that’s designed to be installed without cutting any additional holes in your ceiling. Check the label to make sure the box is designed to support more than 35 lbs.
Most ceiling boxes are large enough: The NEC dictates how many wires and clamps you can safely put in an electrical box. Typical 1-1/2 to 2-in. deep octagonal or round ceiling boxes are quite large and overcrowding is rarely a problem. Even so, you should run through the calculations to be sure. See the section on “Calculating Box Sizes.” But if you encounter a round box that’s only 1/2 in. deep, replace it. Once again, the easiest way to install a new electrical box in an existing ceiling is to use a special fan brace and box made for retrofitting.
Calculating Box Sizes
To figure the minimum box size required by the National Electrical Code, add: 1 for each hot and neutral wire entering the box, 1 for all the ground wires combined, 1 for all the clamps combined, and 2 for each device (switch or receptacle, but usually not light fixtures) installed in the box. Multiply this figure by 2 for 14-gauge wire and 2.25 for 12-gauge wire to get the minimum box volume in cubic inches. Plastic boxes have the volume stamped inside.
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