Dear Mr. Electrician: I want to replace a very old ceiling light fixture in a very old house. After removing the ceiling canopy cover that hides all the wiring, I found that there isn’t a standard ceiling electrical outlet box. Instead, there is a black round disc (about 3 inches in diameter) which has a 1 inch long screw type rod sticking out of it. The wires are around it. The light fixture that I want to install comes with a flat hanger bracket and the instructions tell me to install this hanger bracket onto the outlet box. Since there is no outlet box, I don’t know what to do. What are my options?
Answer: I suspect that the round disc is actually an old black enameled metal pancake box. It’s approximately the diameter and thickness of a hockey puck and made out of metal. An old gas pipe usually protrudes from the middle of this pancake box. A setscrew tightens the box to the gas pipe.
This is how old houses that originally had gas lighting converted over to electric lighting. The pancake box was mounted onto to an existing and disconnected gas pipe. The cables were attached to the pancake box and splices were made. An additional fitting or two was threaded onto the gas pipe to support the light fixture which was made for this type of installation. The canopy of the old style ceiling light fixture acted as the junction box for the spliced wires.
Around the pancake box are four holes, each with a setscrew or clamp which engages the cable, preventing it from being pulled out, and provides electrical continuity for the equipment ground for the armored cable.
The wiring is most likely armored cable (BX), however ungrounded non-metallic cable (The Type Before Romex), or knob and tube type wiring is possible as well.
Beware if the gas pipe has a cap on it. Usually the caps are removed when the gas line is taken out of service. However, until you can verify that the gas line is dead you should not remove the cap.
In a situation such as this, the best thing would be to install new wiring. However this not only could be expensive, but damaging as well. Walls and ceilings may need to be broken open to re-route old dried and brittle cables and install new wiring.
Turn off the power. You will need to remove the old pancake junction box. Do it carefully so as to not damage the existing wiring. Often, wiring from that era of home construction now has dry, brittle insulation on it. Any disturbance to the wires could cause the insulation to break off.
Make sure that you identify each conductor in the box before you take apart the splices. The color coding is almost gone on these wires. The wires are likely to be soldered and taped. The insulation on the wires will break off as you separate the conductors. Get a roll of white and a roll of black electrical tape. You may need rolls of red and blue electrical tape also.
The gas pipe will be a hindrance to installing a new modern octagonal ceiling electrical box. Also it is quite likely that there is a piece of wood supporting the gas pipe or the pipe may be attached to the side of a ceiling joist.
Sometimes a pipe wrench can be put on the gas pipe to unscrew it from the elbow. An internal pipe wrench might be needed. Other options are cutting it out with a multi-function oscillating tool or a reciprocating saw, or relocating the ceiling box. Relocating may not be an option due to the existing lengths of the wires.
Once all obstacles have been removed and the existing cables have been identified and taped, a new electrical box can be installed. An old work ceiling fan brace and box can be fitted in place through the existing hole. A side mount type is also available if the joist is right there. Try to get the deeper boxes.
Use the proper connectors and anti-short bushings for the cables and bring them into the back of the box. In this case it may be best to put connectors on the ends of the cables with the locknuts removed. Tape the ends of the wires together. As you push the box into the ceiling, pull the cables through each connector. Tighten the locknuts by hitting them with a screwdriver driven by a hammer after the box is secured to the bracket. The BX metal armor is the grounding conductor, so it needs to be a tight connection.