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Front and Rear of an Old Style Ceiling Electrical Pancake Box for Knob and Tube Wiring

Replacing a Very Old Style Ceiling Electrical Junction Box in 2019

Dear Mr. Electrician: I want to replace a very old ceiling light fixture in an old house. After removing the existing light fixture ceiling canopy cover that hides all of 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 the 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.  Sometimes an old gas pipe protrudes from the middle of this pancake box instead of a fixture stud.  A setscrew tightens the box to the gas pipe.  NOTE: Text links below go to applicable products on Amazon.com. Old Style Ceiling Electrical Boxes That was how old houses that originally had gas lighting converted over to electric lighting.  The pancake box was mounted onto to an existing 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. Other types of old pancake boxes were mounted directly onto ceiling joists using wood screws.  Instead of an opening for a gas pipe, they would have their own fixture stud for attaching a light fixture to.  The fixture stud had the same size thread as a gas pipe of the same diameter. 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 where the original wiring insulation has degraded, the best thing would be to install new wiring.  However that not only could be expensive, but damaging as well.  Walls and ceilings may need to be broken open to re-route or remove old dried and brittle cables and install new wiring. Replacement of Old Style Ceiling Electrical Box 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....