The Sparking Light Switch

June 16, 2009

Stuart Paterson relates a story that happened to him a number of years ago. He’s from Scotland, so don’t let the high voltage cited alarm you:

“A friend had asked me to have a look at a light switch in her house. Every now and again they got an electric shock when switching on the light. Our mains is 230V so the shock was sometimes quite painful, and I’m sure it was pure luck that no one had been injured. As she rented the property, my friend had contacted her landlord numerous times. In fact, three different electricians had been out to have a look at the switch. It had been replaced twice.

I removed the switch and checked the wiring, which looked okay. I then checked for continuity between the earth point on the switch and a radiator on the other side of the room. It checked out fine, and as I could see no other fault in such a simple device, I was stumped.

Just then someone walked in the room and a big spark flashed on the radiator where I had terminated the test wire. The wire was lying on top of a metal strip holding the carpets down between the door frame. It was then that the fault dawned on me — the metal strip had been screwed down with screws that were far too long. When someone stepped on the metal strip their weight caused it to sag slightly, pushing the screw into what I can only presume was a live cable below. When a person touched one of the metal screws securing the light switch, they completed the circuit and got a shock!

The fix involved simply changing the screws for ones of the correct length.”

Posted by Karen Field on June 16, 2009 | Comments (5)

July 23, 2009

In response to: The Sparking Light Switch
William Ketel commented:

Probably there should have been some digging into just what damage had been done to whatever conductor had been the source of voltage. Unfortunately, such an investigation would probably require a great deal of digging and dismantling, and if there was real damage, a whole lot more effort to replace the damaged cable. So just hope that, if the conductor was damaged, that an oveload never happened.
Of course, I would recommend installing a smoke detector.

July 21, 2009

In response to: The Sparking Light Switch
Dr Zapp commented:

Reminds me of my tech school days. My neighbor in the YMCA was a ME student, and he had a daily routine of comming into my room, borrowing something off the desk and walking out, closing the door and turning off the light without saying a word. Of course I could have just kept the door closed, but that wouldn't do. It was getting near the end of the semester and I had to do something creative. The light switch had a grounded wall plate, and he never wore shoes in the building. I had a storage battery in my room running a car radio, so I brought in a Model T ignition coil and wired it to the doorknob with #22 brown enameled magnet wire for camoflage, also ran a strand up the side of the door and zigzagged on the rug in the doorway. With the charger on, the battery had continuity to ground via an autotransformer. Next time he did his thing, I stepped on the switch under the desk. His exit was rather dramatic. I got him 3 times before he figured out it wasn't the wall plate that was hotwired! Then one day I came back from the loo to find my door closed. I was pretty sure he was waiting for me at my desk, in his socks, and that the charger was turned off (2-pole switch). I borrowed some wire from another EE, grounded my key to a wall outlet in the hall, and inserted it in the keyhole. A howl a few choice words confirmed my suspicion and my countermeasure. Didn't fry the radio either (all tubes).

July 16, 2009

In response to: The Sparking Light Switch
zig4justice commented:

that's a great story -- and great find!
Changing screws=done -- definitely a rental property. ;)

July 1, 2009

In response to: The Sparking Light Switch
Daleb commented:

the stip abd and floorboards should be lifted and the damaged cable repaired/replace

June 26, 2009

In response to: The Sparking Light Switch
joe commented:

Should the wire not have been at least looked at under the carpet strip ?

Design News Partner Zones

Light Matters: The Unsung Heroes of Modern Health Care
First, let's define "no-compromise." In an ideal configuration, this lamp would use a high-brightness LED (HBLED) that is built into a small, integrated package and is able to produce a large quantity of focused light, operate with a high level of reliability and generate no audible noise. Is this difficult? Yes, but it is possible.
Read More

Design Engineers' Portal for Sensing and Machine Safety
Whatever industry you're in, or whatever product you manufacture, the right sensors to automate your plant, and to improve your overall efficiency, quality and safety are a must. You'll find Banner Engineering to be an amazing resource of products, training and people with expertise.