Broken light bulb cuts power to part of garage and house
From the desk of Instructor Jimmie Slemp
(Just as with old police shows, names have been omitted to protect the innocent and not-so-innocent.)
I was in the garage doing some work and I happened to be using a drop light with an incandescent bulb in it. Somehow I knocked the light over and it hit the ground and went out. This really didn't surprise me; I figured that the impact of the fixture had broken the light filament.
Well, that turned out not to be the case-- although I didn't realize it at the time, (the garage door was open and there was still some light outside), some of the other garage lights had gone out, too. Now I was beginning to think I had a bigger problem on my hands. I walked into the house, only to find a major portion of the house lights were not working either. If only I knew an electrician ... oh, wait. I dug out my meter and proceeded to the panel. While I was going to the side of the house I observed my neighbors across the street in the garage and they had lights on and music playing.
I decided to check voltage at the panel and everything seemed to be normal. I must admit, I was really beginning to wonder... what could it be? At this point I decided to step back, take a deep breath, and use one of the most important tools in troubleshooting: the power of observation. This involves asking yourself questions like, "What is the situation?", "What isn't working?", "What is working?", and "What are the probable causes?" I went back into the house and took a closer look. What I had originally thought was half the house turned out to be only a few lights and was probably only one circuit.
So at this point, what would you do?
I thought, “What’s the closest outlet (receptacle) to the panel that isn’t working? As it turns out, the receptacle that the drop light was plugged into was only 5 to 10 ft from the panel. It was the receptacle that the garage door was plugged into. I grabbed a ladder and-- as I reached to unplug the cords that were plugged into the receptacle-- I could hear the faint sound of sparking and the garage lights flickered. Yes, I was another casualty of the “backwire burnout”. What is backwire burnout? Often the wiring methods employed in residential construction utilize terminal pressure connections (stabbacks). Over time, and sometimes with heavier loads, these connections become loose and build up resistance until they finally fail. It is an interesting occurrence, in that branch circuits loads are connected in parallel, but this particular wiring method actually creates a little series-type connection and when it fails all of the devices down the line will no longer work. Anyway, I removed the receptacle and replaced it with a new receptacle and “pigtailed” the wiring connection. Everything worked “a-okay”.
This leads me to a follow up comment and question. Many electricians believe that you cannot use the backwire wiring method to install receptacle and switches. I say, 1) manufacturers are not in the business of making products that cannot be used in practical field applications, and 2) where in the NEC does it prohibit this wiring method?
Now on the other hand - there is a specific type of circuit, and an NEC article that does limit the use of these backwire connections ... can you name the circuit and identify the NEC article?