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Posted By: Scott35 Tent OOPS!!! - 06/24/06 02:21 AM
*** Submitted For TwinCitySparky ***

****** TENT OOPS!!! ******

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Hello!
I thought this might be good for the photos for discussion area.

Last Thursday, while working at a church, the maintenance coordinator walks up and asks for my opinion.
We walk outside and he shows me this tent that they just put up for their big anniversary celebration.

He said the 25 tent assembly guys who were putting it up were continually getting shocked, as they touched the metal poles and such.

The parking lot lights were marked and de-energized.

The tents imbedded power/lighting cords that were not connected to anything, were humming and buzzing!

I gave a brief explanation of inductance, pointed up at the 72KV ?? lines and said I thought they might want to move the tent.

An hour later, after he talked to 2 masters at different companies, he approached me again with the tent assembly personnel and said:

"One master told him grounding the tent would help."

I pointed at the 150 or so 10' steel anchors that they jackhammered into the parking lot around the tent and said:

"Might not help much".

He then said another master told him that the POCO could place rubber maintenance service covers over the wires to lessen the effects and danger!

I then said I thought he should contact the POCO right away.

After hearing them say MOVE IT NOW! He decided to shoehorn it into a distant lot.

The tent personnel said they never ran into this before!!!

I wonder who will pay for the move? The 3rd pic shows tent after being moved.

Yikes! [Linked Image]

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*** Moderator's Note: Thanks to TwinCitySparky for the submissions!

New / Posted 06-23-2006 by Scott35
Posted By: alan bergold Re: Tent OOPS!!! - 06/26/06 02:09 AM
I cant believe that happened ,the power lines are at least 20 feet from the tent,are you sure thats why they were getting zapped,and if so how bad were the shocks and was it a wet day .??????
Posted By: e57 Re: Tent OOPS!!! - 06/26/06 02:25 AM
I think they are 30-40' from the tent, but poles are 20' closer to them than someone on the ground. I think that difference in potential/distance could be enough for a small zap.
Posted By: Dnkldorf Re: Tent OOPS!!! - 06/26/06 02:29 AM
I would wonder if they have the same problem with the light poles in the picture?
Posted By: JoeTestingEngr Re: Tent OOPS!!! - 06/26/06 10:55 PM
I think this is definately one of those places where the Fluke and the Wiggy will get you different readings. The light poles are at right angles to the wires so I doubt there is much coupling.
Joe
Posted By: iwire Re: Tent OOPS!!! - 06/26/06 11:47 PM
Joe.... [Linked Image]
Posted By: TwinCitySparky Re: Tent OOPS!!! - 06/27/06 06:34 AM
No rain or moisture at all. The poles are about 30'- 40' feet from the wires. The lot lights which are parallel to the lines but further away did give me a "lighter" version of the shocks happening at the tent when I was replacing bulbs. The shocks at the tent were intense enough to cause discomfort. It's hard to tell from the pics but the tent poles are about 10' higher than the lot lights and as you can see, the position of the tent is actually beneath the lines. I was able to draw almost a 1/2" arc from the poles. Every 2nd or 3rd cable that was sewn in to the tent was vibrating intensely. I was surprised they were almost done putting it up. That must have been a long day for the workers as they repeatedly got shocked. They were trying to complete the building process by pushing each of the main tallest poles into a perfect vertical position. That is when the shocks became even more intense and they finally thought they should ask someone about it.

[This message has been edited by TwinCitySparky (edited 06-27-2006).]
Posted By: mamills Re: Tent OOPS!!! - 06/27/06 12:56 PM
I don't know the slightest thing about any of this, so somebody please set me straight. Could this be caused by some type of leakage from one of the insulators on one of these towers (even though I'm assuming that these towers are supposed to be grounded)?

Also, I wonder if the tent setup people got as far as they did because they were wearing gloves while working?

Mike (mamills)
Posted By: Rewired Re: Tent OOPS!!! - 06/27/06 09:48 PM
Mike:
The whole thing is acting like a transformer in a sence.... The current flowing in the lines overhead is creating a magnetic field around each of the lines ( in this case a very strong one).. The magnetic field in turn is now generating (inducing) a voltage in the metal work of the tent poles and lighting and power cords and what ever was present at the time...
There is no electrical "leakage", its just being in the wrong place period..

Personally I am amazed that Twincitysparky was able to draw a 1/2 arc off one of the poles.. What was I told once,roughly 33,000 volts jumps something like a 1" air gap???? ( depending on conditions) So that would equal about 16,500V present at the poles, albeit the current would be so minimal it would be very uncomfortable to be in contact with, yet still VERY unsafe..

A.D
Posted By: Larry Fine Re: Tent OOPS!!! - 06/28/06 12:39 AM
For effect, have someone hold a fluorescent tube inder the lines.
Posted By: Scott35 Re: Tent OOPS!!! - 06/28/06 04:31 AM
Quote

For effect, have someone hold a fluorescent tube under the lines.

Definitely will display the overall field effect taking place at this location!

The Lamp will illuminate - possibly near 1/3 of the intended output.

Scott35
Posted By: TwinCitySparky Re: Tent OOPS!!! - 06/28/06 05:12 AM
http://news.bbc.co.uk/1/hi/england/bristol/3509651.stm
Posted By: RODALCO Re: Tent OOPS!!! - 06/28/06 07:40 AM
Those lines look to carry a higher voltage than 72 kV to me.
More like 132 or 275 kV looking at the strings of disc insulators.
We use 12 for 220 kV in NZ this looks like 16 discs to me ( 275 kV ? )

Very likely that magnetic fields induce eddy currents in the steel tent poles and cause a possible voltage build up.

What are the Grid / POCO poles made off, concrete or steel ?

A possibility is that one Grid / POCO pole is partially live due to a faulty insulator string, either in the steel or via the reinforcing steel.

Might pay to get the Grid / POCO asset owner to check out their poles for leakage and check up with the local regulations re safe working distances for temporary buildings, tents near these lines.

If to close, this is a very dangerous situation.
Posted By: TwinCitySparky Re: Tent OOPS!!! - 06/28/06 11:49 PM
Rodalco - They do appear to be steel poles. I wonder how often things like this happen with resulting tragedy. I must say I was very surprised that none of the 50 or so people involved with this whole fiasco realized there was any significant danger. After seeing this all unfold, I cant help but think that large warning plaques placed on the base of the poles (for the clueless among us) outlining minimum approach distances etc. - might save a few lives...
Posted By: mikesh Re: Tent OOPS!!! - 06/29/06 04:59 PM
I had a similar experience at a light fixture in a parking lot. The fixtures were below a 250 kv transmission line and one of the lights was not working. I was commisioning the lights for turnover to the owner. I got my trusty 12 foot wooden ladder and set it up beside the pole mounted fixture and as soon as I touched the fixture i got a shock. I started cursing the guy who wired this thinking he did not bond the pole. Down at the ground I removed the access cover only to find the bonding conductor was well connected. I got my Fluke meter and tested the voltages phase to ground and phase to neutral as well as neutral to ground. 120 volts and all connections were good. So I opened the connection because I thought the ballast must have some high impedance leakage and up the ladder i go and get a shock when I touch the fixture. Now I am swearing agin but I am not sure at whom. It was at this moment I look up and think about those transmission lines. I touch a test lead of my meter against the fixture and hold the other lead in the air and get 140 volts. I raise the open lead higher and the voltage goes up. As high as I could reach I get about 170 volts. At the ground i get 50 or 60 volts. I expect it is just the field around the wires and perhaps capacitive coupling. I don't really think it was a particular hazard for a healty guy like myself but definitely uncomfortable. After this I decided I would never live under transmission lines.
Posted By: gideonr Re: Tent OOPS!!! - 06/29/06 09:59 PM
As for the length of the arc, there's a difference between how far a voltage can jump across an air gap that didn't already have an arc, and how far you can pull out an arc starting from a zero gap.

I also think this is capacitive coupling, there isn't usually all that much current in the cables, cos current makes power loss (I2R) where higher volts keeps power loss down. 20'/60' * 33kV = 11kV into a very high impedance, but a lot less into a human touching it. Don't go near!
Posted By: Theelectrikid Re: Tent OOPS!!! - 07/03/06 06:05 AM
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For effect, have someone hold a fluorescent tube under the lines.

I do that all the time under the 100-300KV (Don't quote me on that) lines behind my house, mainly to amaze my friends.

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After this I decided I would never live under transmission lines.

Too late for me, there's ones behind me. There used to be houses at the ends of the drainage depression, but they were demolished when the 100-300KV transmission lines went up. I'd hate to live in an aluminum-sided trailer under a set of transmission lines.

Ian A.

[This message has been edited by Theelectrikid (edited 07-03-2006).]
Posted By: Luketrician Re: Tent OOPS!!! - 07/10/06 06:26 AM
Just take your volt tick and point it up and see if and glows at ya next time you are around a switchyard or trans, lines. That never gets old for me. Very good explanation of the transformer effect, "inducing a voltage onto the poles" . Kudos Rewire!
Posted By: Celtic Re: Tent OOPS!!! - 07/10/06 08:39 PM
Try it with a flores. tube [Linked Image]
Posted By: Rewired Re: Tent OOPS!!! - 07/11/06 10:17 PM
I am gonna try it with a Fluorescent tube next time I am out walking..... I tried it with my " stupid stick" as I called it and it didnt glow until I went up and touched it to the metal of the tower!
A.D
Posted By: Luketrician Re: Tent OOPS!!! - 07/11/06 11:28 PM
The fluke brand volticks are not as sensitive as the greenlees. For ex, with myself standing under 500kv round bus, that little greenlee WONT stop going berzerk until I place it within 2' of the ground. I believe the clearance we have here is 35' from ground to bus.
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