Electrical Basics: Installing An Incandescent Ceiling Light Fixture

By Bruce W. Maki, Editor

Installing a light fixture is a reasonably simple project that most people can do.

But... I know you know this... the power must be turned off first. The safest and surest way is to turn off the breaker that supplies power to the light fixture.

Sometimes... turning off the power to a light fixture can be as simple as turning off the switch... but not always. It depends on how the wiring was initially installed. 

The simplest way to tell is by removing the screws that hold the fixture to the ceiling, to get a look at the wiring in the junction box.. Obviously, the glass globe or cover must be removed first.

• If there is only one cable (a cable is a group of wires bundled together by a wrapper) in the junction box, (like the example in this article) then the power must come from the switch. (Note that this means that the switch's junction box must contain at least two cables, because one goes to the light, and the other must be an incoming "hot at all times" cable.) 
• If the junction box behind the light fixture has more than one cable, then one of those cables is possibly "hot at all times", in which case the only way to kill the power to the entire junction box is to turn off the circuit breaker.

I strongly recommend buying a non-contact voltage tester, which lets you check for power without removing any wire nuts. This neat little device (about $12 at Home Depot) looks like a fat pen, and beeps when the tip comes near a live wire.  But... don't ever trust the tester's silence... always check that it works by first verifying the tester on an outlet that you know is working. 

The junction box is ready to go. The wires were spread out and cut to a reasonable length. I used a sharp knife to carefully make a slit along the center of the cable jacket, then pulled the slit jacket away from the wires and lopped it off.  I left about 6 inches of wire sticking out.

I stripped about 1/2" of insulation from the end of each wire.

I spread out the parts on the floor to make sure everything was there. I almost always use my own wire nuts instead of the tiny nuts provided with the fixture.

The metal bracket was installed into the plastic junction box. I often use a cordless drill/driver here... but use caution... too much torque can strip out the plastic.

The ground wire (the bare copper wire) was installed under the green screw in the bracket. The wire must be snug. I pushed the ground wire into the back area of the box, to keep it out of my way. Next, the long machine screws were threaded a few turns into the holes in the bracket.

The fixture had a white and a black stranded (flexible) wire. Most fixtures have the wires stripped already.

Making proper connections is crucial. I held the supply wire (the top wire) beside the the fixture wire, so the ends were aligned.

Then I twisted the bare ends of the wires about three turns. The flexible, stranded wire will wrap around the stiff, solid wire. Sometimes I strip the stranded wire an extra half-inch, so it can wrap around the solid wire several times, otherwise the stranded wire may come out of the wire nut.

I screwed the wire nut onto the bare wire ends. I twist the nut firmly, until the insulated portion of the wires start to twist. I always tug at each wire to see if it pulls loose.

Some electricians wrap all their wire-nutted connections with electrical tape. This extra step takes a minute or two, and probably can't hurt anything. I don't normally wrap wire-nutted connections in tape.

Light fixture connections are basic: The white (neutral) wires connect together... And the black (hot) wires connect together.

If a fixture or device (such as an outlet) has screw terminals instead of wires, then the connection protocol is:

I tucked the wires into the space in the junction box. I try to keep the white wires separated from the black wires, just in case something ever goes wrong, such as a wire nut working loose. Physical separation can't hurt, might help.

I held the fixture base next to the mounting screw, to determine if the screw hung down far enough.  I hate it when I'm trying to install the fixture and the screws aren't protruding far enough to poke through the holes in the metal base. I'd rather the screws stick out too far than not enough. Note the keyhole shape of the holes in brass base.

I slid the base upwards so the screws poked through the holes.  Since this fixture had fiberglass insulation in the base, it's hard to see the screw heads while orienting the base.  It took several attempts to get the screws to come through the holes.

Once both mounting screws were through, I rotated the base slightly, and then tightened the screws.

The completed light fixture after the bulb and glass globe were installed.

Copyright © 1999-2003  HammerZone.com

Written May 1999
Revised June 7, 2003