This is a short but true story about a recent installation job that quickly turned into a trouble shooting job.
How can hardboard siding be live?
A customer wanted me to relocate a cable TV jack and install an electrical outlet on the wall for a LCD TV. There were no problems with the electrical outlet and it went like clockwork so I moved on to the TV jack. The location she wanted the TV was on an exterior wall. Her existing cable was fed from the outside of the home and was long enough to reach the new location so I drilled a small hole through the wall and proceeded with feeding the cable through the wall.
As I pushed the cable inside I noticed a small electrical spark. Where did that come from? Did I accidently drill through a wire? I went inside and looked in the access hole I made for the cable jack to see if there were any wires where I drilled through but there were none. I went to get my volt meter to verify that there was indeed voltage present and sure enough the meter read 60 volts when I probed the hole and grounded off to the cable TV connector. Then the voltage disappeared and reappeared several times so there was an intermittent connection to something live but what was it?
No question about it, I had to find and remove the connection to the electrical system before someone got hurt or worse. I called the home owner in and told her that we had a very odd situation occurring and we needed to get it resolved. Due to the danger, she agreed and told me to do whatever it took to solve it. I told her that I had to open up the wall since I really didn’t have any other options. It was at this time that she told me that some exterior siding had been replaced on that wall several months back. Now I know what I am looking for, a nail in a cable.
After I opened up the wall I quickly discovered that they had put foil backed insulating foam sheets under the siding and used very long galvanized nails to attach it with.One of the nails had slightly penetrated a cable where they missed hitting the stud so the cable damage was minimal. That explains the intermittent connection. I was able to cut off the nail and re-insulate the cable without having to replace it.
In this case I did not remove the F connector since I was relocating an existing cable feed and since the F connector was connected on the supply end it was grounded. When I pushed it through the wall it made contact with the energized foil that created the spark. I never would have been aware that the foil insulation was energized and it would have remained a hazard had I not removed the grounded F jack before I inserted it in the wall.
You can see the large nail penatrating the cable jacket below and you can see the foil foam board in the background.