How to Install a Ceiling Light Fixture

Turn off the power and remove the old fixture

Turn off the power to the light fixture. Make sure the wall switch is off, but don’t stop there; you should also turn off the breaker that controls the circuit at the main circuit panel.

Remove the nut or screws securing the dome-shaped canopy and lower the canopy to expose the wires. Test the wires to make sure the power is off. Move the tip of a non-contact voltage detector near each. If the tester lights, switch off circuit breakers one at a time until the tester light goes off.

When you’re sure the power is off, disconnect the wires from the light fixture, leaving other wires in the box connected. Then remove the screws securing the crossbar to the electrical box and lower the fixture.

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Buy a new fixture

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 create a fire hazard. Wires manufactured after 1985 are required to have coverings that can withstand higher temperatures.

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.

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Check the electrical box for capacity and strength

Check strength: 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. This includes almost every type of ceiling box.

Your electrical box should be securely fastened to solid framing before you hang a new light fixture from it. In addition, a light fixture that weighs more than 50 lbs. has to be supported independently of the electrical box. An easy way to do this 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 capacity: 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 below). If you encounter a round box that’s only 1/2 in. deep, replace it.

Calculating box sizes

To figure the minimum box size required by the NEC for your fixture, add:

• 1 for each hot and neutral wire entering the box;
• 1 for all the ground wires combined;
• 1 for all the clamps combined;
• 2 for each device (switch or receptacle, but usually not light fixtures) wired inside 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. Check this against the volume stamped inside the box.

Nikolin recommends choosing a box that’s slightly larger than required according to your calculations to prevent overcrowding. “Overcrowded boxes can cause a fire,” he warns.

Turn on the power and test for hot

Turn the power to the light back on at the main circuit panel and turn on the wall switch. Use the non-contact tester again to make sure there is power to the hot circuit wire, which is usually red or black.

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Test for ground

Touch the leads of a double-lead voltage tester to the hot wire and the metal box (or the bare copper ground wire, if you have one). If the tester lights, the box or bare wire is grounded, and you can proceed. If the tester doesn’t light, that indicates there is no ground. This usually won’t happen when you’re testing a bare ground wire, but it might happen if you have a metal box that isn’t connected to a ground wire.

Once you’ve completed testing, turn off the wall switch and the power at the main circuit panel before continuing.

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Add a ground wire to a metal box

Most light fixtures have metal parts, so if you’re hanging one from a metal box, the box has to be grounded for safety. To do this, wrap the end of a six-inch length of bare copper wire around a No. 10-32 ground screw and drive the screw into the threaded hole in the bottom of the box. Tighten the screw to secure the ground wire and twist the wire to the bare ground wire in the box. When you install the light fixture, you’ll add the fixture ground wire (green or bare) to this wire pair.

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Preassemble the mounting strap assembly

The key to an easy installation is assembling and adjusting the parts before you climb on the ladder.

Mounting with treaded pipe: Align the back of the canopy (the side that fits against the ceiling) with the crossbar and turn the locknut until about 3/8 in. of the threads on the screw collar loop extend through the canopy. Lock the threaded pipe in this position by tightening the locknut against the crossbar. See the illustration at this link:

Mounting with screws: Align the crossbar with the back of the canopy and adjust the length of the screws or rod to protrude about 1/4 to 3/8 in. through the canopy. Tighten the locknut(s) to hold the screws or rod in this position. For hanging fixtures, adjust the length of the chain by removing lengths, but don’t cut the wires shorter until you’ve hung the fixture and confirmed that it’s the right height.

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Screw the crossbar to the box

Position all the wires to one side of the crossbar, then screw the crossbar to the electrical box with the screws. You may need a helper to support the fixture if you can’t rest it on the top rung of the stepladder.

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Connect the wires

Connect the neutral wire from the light fixture to the neutral white wire(s) in the box. If your fixture is wired with lamp-style cord rather than white (neutral) and black (hot) wires, identify the neutral wire by looking for silver conductors, writing, squared corners, or ribs or indentations on the insulation.

The hot wire is usually black, but if you have a lamp-style cord, it will be the unmarked wire. Connect it to the hot (black or red) wire in the box.

Complete the hook-up by looping the ground wire clockwise around the ground screw on the crossbar, tightening the screw, and connecting the end of the wire to the ground wire from the light fixture.

Screw wire connectors onto each set of wires (neutral, hot and ground) that you twisted together.

• Pro tip: You might have to strip some insulation to expose the ends of the wires. “Be careful not to nick or damage the inner wires, as this can weaken them and lead to issues like short circuits or poor connections later,” cautions Nikolin. The best way to avoid nicks is to use a wire stripper instead of a knife.

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Close the box

Fold the conductors into the ceiling box and slide the canopy over the protruding threaded support. Secure it with the decorative nut to complete the installation.

CAUTION!

If you have aluminum wiring, don’t mess with it! Call in a licensed pro who’s certified to work with it. This wiring is dull gray, not the dull orange that’s characteristic of copper.

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FAQ

Why is aluminum wiring considered dangerous?

The electrical conductivity of aluminum is lower than that of  copper, and aluminum has a higher coefficient of thermal expansion. Aluminum wires have to have a wider cross-section than copper wires to carry the same amount of current, and they expands more when they get hot. Over time, repeated expansions and contractions at aluminum-to-copper splice joints result in loose connections, electrical arcing and fires.

How much does it cost to replace a ceiling fan?

Not including the cost of the new fan itself, the cost of having a pro replace a ceiling fan is generally between $60 and $200. This assumes you are reusing the original wiring. If you move the fan and have to install new wiring, plan to spend about $200 extra. Other factors, such as an exceptionally high ceiling or particularly large fan that requires extra bracing , can further drive up costs.

About the Expert

• Sergey Nikolin is an experienced electrician and HVAC specialist. He is the President at Product Air Heating & Cooling LLC in Everett, Washington.

Next, learn how to replace a pull-chain light fixture.