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Rob Spiegel
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Blogger
Re: Ungrounded Wires Can Kill
Rob Spiegel   7/3/2011 2:33:18 PM
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Sad story. With all of the Sherlock tales, the only ones that end up deadly are the ones where the victim becomes the grounding path.

MYRONB
User Rank
Gold
Ungrounded Wires Can Kill
MYRONB   7/2/2011 2:33:27 PM
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At a tanning plant, while raising a load, the mast of a forklift smashed into the socket of a 220Vac fluorescent overhead lamp.  Unbeknowst to the driver, the forklift frame was now energized by the 220V line.  The forklift driver dismounted the lift to dump his load of hides into the tank before lowering the forks. While doing so, he touched both the forklift frame and the tank.  The driver became the ground path: lamp fixture to forklift to driver to the caustic tank.  The tank had a circulating pump that was (correctly) grounded.  He received a fatal shock.  The story is told in more detail in "The Case of the Lethal Lamp," in the May 18, 2009 Design News Magazine.

 

 

Technophile
User Rank
Bronze
Re: The joys of home ownership
Technophile   6/30/2011 6:35:35 PM
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Not a good idea for the customer to skip finding the fuses while the lights are still on.  Gets harder in the dark... 

Hope you informed them that this was a serious safety hazard and pressed them a bit to have it fixed.  While I understand that the customer doesn't know electricity and might back away from doing anything because they're uncomfortable, don't really understand and don't want to spend the money, it will be a lot less comfortable and convenient if they put off fixing it until after someone gets a fatal shock.

BTW, I'll guess that "whollah" is "voila", pronounced "vwah-lah", a French word.

 

rcwithlime
User Rank
Silver
Re: The joys of home ownership
rcwithlime   6/30/2011 5:00:54 PM
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I had installed  additional lighting in a very old store as well as replacing the light switch.  I made the final connections live. After completion, I turned the switch on and some of the original flourescent lights dimmed dramatically while the newly installed lights lit up at same dim level.  Turn the swith off and original lights brighted again, while new installs went out. 

Now  store owner now wondering if I had a clue as to what I was doing. Not a fun position to be in. The switch conduit box had the hot pass through wire, so naturally I had connected the ground wires to the metal box.  As luck would have it, the battery had died in my multimeter, but as this was not rocket science,I did not believe that I really needed a meter to verify the problem, so no need to run to the store for another battery. So, I  removed switch and made the contact closure by just touching the lead together. All lights came on as they were supposed to. As rediculous as this seemed, I replaced the light switch, put the cover back on, flipped the swith and problem was there again.

Ok, so what is the difference between making the light power contact closure by using a light swith or by touching the leads together manually? Nothing! So what else changed? Only ground point for the ground wire was one of the screws that also held on the metal cover. That ground to the switch box was lost when I removed the switch. So, I replaced the switch, left the ground off, and Wholla, lights illuminated! Issue is when gound placed onto fixture, problem appears.

Someone has the neutral and hot leads reversed somewhere down the line. Customer was advised. As he was not even sure where the fuses were for the store, he decided to let this go for a future time. Eventually I heard that several years later, another contactor had found the same problem when they installed additional fixtures and pull their wiring off the same branch circuit. This has now been corrected with new runs from a new load center.

Rob Spiegel
User Rank
Blogger
It's always the ground
Rob Spiegel   6/29/2011 6:08:01 AM
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In our many Sherlock Ohms mysteries, one of the most common challenges is finding the solution to a home or building's electrical peculiarities. Almost invariably, the problem traces back to some off-reservation electrical work that wasn't properly grounded. In one case, the problem resulted in the loss of life: The Case of the Floating Dock.

Tim
User Rank
Platinum
TV cables
Tim   6/25/2011 9:03:35 AM
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That is quite lucky that your TV did not short out or fry your video card.  The new LCD and plasma TV's are great, but they are significantly more fragile than the old tube models.  During a move, one of our 19" tube TV's dropped about 6 feet to the ground and only had some casing damage.  The picture was fine.  I do not think that my 42" plasma would survive the same drop.

 

Charles Murray
User Rank
Blogger
The joys of home ownership
Charles Murray   6/24/2011 12:41:20 PM
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The key sentence here is, "...whoever wired this circuit didn't bother to connect the ground from receptacle one back to the breaker." Having owned three old houses, I can attest to the fact that older homes often get worked on by "handymen" who aren't quite as handy as they think they are.

Jennifer Campbell
User Rank
Gold
Re: Let Us Know abour Your Sherlock Moment
Jennifer Campbell   6/24/2011 12:28:16 PM
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Your challenge/solution may even make it into print. Be sure to submit a minimum of 500 words in order for a chance to see your byline in Design News!

Rob Spiegel
User Rank
Blogger
Let Us Know abour Your Sherlock Moment
Rob Spiegel   6/24/2011 12:10:05 PM
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We are always seeking to hear your stories of odd and knotty engineering or design challenges. Please send them along. We can't promise fame and fortune, but we can deliver plenty of juicy comments.

Send your problem-and-solution story to rob.spiegel@ubm.com

 



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