Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[Mike Sokol]

Here's another thing you might not be aware of, but certainly a possibility for any spring outside gigs you may have coming up. (remember spring?) If a large surface is anywhere under high-tension power lines, there can be significant voltage and moderate current induced from inductive coupling. I've heard this complaint numerous times from RV owners who park their camper under high-tension lines overhead, then feel painful shocks when they touch the side of the RV and the ground at the same time. This is also a big problem for farmers who often lease the right of way on their land to power companies. They have to temporarily "ground" any irrigation pipes they're taking off the truck, especially if they're parallel to the power lines overhead. And my PoCo buddies warn me that parking their truck under a high-voltage line will zap them when stepping out of the truck.

Here's a great paper on the subject written by Bonneville Power.

http://www.bpa.gov/news/pubs/GeneralPublications/lusi-Living-and-working-safely-around-high-voltage-power-lines.pdf

I've talked to the author of this paper, and they tell me there can be "significant voltage" on something as large as a semi-trailer or RV parked under lines. When I asked how much voltage, they told that a car's spark plug attached between the vehicle bumper and a ground stake would continuously spark. Yikes, that's got to be a few thousand volts. But not to worry, they said the induced current was less than 5 mA, so it's not deadly. Still, that's like grabbing onto an electric fence charger and holding on. 

So if your stage is located anywhere under high-tension power lines, I would REALLY be sure it's grounded via an 8-ft ground rod and properly bonded to your generator neutral/ground.

[Steve M Smith]

And you can do this: http://www.larkinweb.co.uk/miscellany/fluorescent_tubes_under_power_lines.html


Steve.

[John Roberts {JR}]

I wonder if the anti-static straps we used to hang from cars would help dissipate the charge from campers?
-----
This is an old story but I was once called by a lawyer who wanted me to be an expert witness for him. His client was suing the power company because he claimed that the voltage in the drop down to his house from the pole power transformer, arced over to his aluminum ladder and threw him to the ground injuring him.

I explained to the lawyer how many volts it takes for the voltage to arc across the tiny speak plug gap (tens of thousandths of an inch), and then how much less voltage is in the power drop. So his client had to be so close to to the power drop wire that it was more likely he actually touched it.

For some reason I did not get hired for that particular expert testimony. I guess my explanation of the facts did not support his case.   

JR

[Steve M Smith]

For some reason I did not get hired for that particular expert testimony. I guess my explanation of the facts did not support his case.

It would have been fun to go along with his story until you got to court, then tell the truth.  Especially if they were paying for you to be an expert witness.


Steve.

[Mike Sokol]

I wonder if the anti-static straps we used to hang from cars would help dissipate the charge from campers?

I've proposed this exact experiment to Fluke and First Energy (my local power company). Fluke will send me a high-voltage probe for measurements, and First Energy has a section of 500,000 volt power lines close to my house with easy road access I can play with. Now don't worry about me climbing up and measuring the power line directly (I'm not qualified or stupid enough to try that). But driving a ground stake next to an RV and measuring the voltage between it and the bumper of the RV should prove interesting. I'll also see if I can find a high-voltage/high-ohm resistor and do a current calculation at the same time. And yes, I'll HAVE to try the spark plug demonstration and take a video if it actually works.

[Jonathan Johnson]

A couple of months ago, The Columbian (the local newspaper in Vancouver, WA) had a writeup about BPA's high-voltage lab at their Ross Complex Facility just north of Vancouver.

http://www.columbian.com/news/2013/dec/09/high-voltage-bpa-lab-a-rare-asset-ross-complex/


P.S. -- Mike, I hate dirty URLs. So I fixed it for you:
http://www.bpa.gov/news/pubs/GeneralPublications/lusi-Living-and-working-safely-around-high-voltage-power-lines.pdf

[Mike Sokol]

A couple of months ago, The Columbian (the local newspaper in Vancouver, WA) had a writeup about BPA's high-voltage lab at their Ross Complex Facility just north of Vancouver.
http://www.columbian.com/news/2013/dec/09/high-voltage-bpa-lab-a-rare-asset-ross-complex/

Gosh, I need a lab like this.

P.S. -- Mike, I hate dirty URLs. So I fixed it for you:
http://www.bpa.gov/news/pubs/GeneralPublications/lusi-Living-and-working-safely-around-high-voltage-power-lines.pdf

Thanks, I've corrected it in the intro to this thread as well. Guess I was just a little lazy....

[Frank Koenig]

Yes, I've experienced this on a couple of occasions. Once we were camped in a spot down in the Mojave Triangle (somewhere east of Barstow, CA) with a beautiful view that just happened to be under a cross-country transmission line. At one point I walked up to my parked motorcycle and pulled a pretty good arc off my finger. I'm guessing that, in this case, I was floating on my rubber-soled shoes and the bike was grounded through its kick stand. I moved away from the lines before fueling from a gas can, and made sure to touch the bike and the can before opening either.

Another time, also in the So Cal desert, a few of us decided to climb a transmission tower (we were younger then -- no further explanation shall be provided). It was cold and dry and I was wearing insulated gloves. When I was about abeam the first set of wires my bare wrist touched the tower. I got a good little tickle and decided it was time to turn around.

On the mode of coupling, are you sure it is inductive and not capacitive? We should be able to come up with an experiment to determine this.

One more aside, don't piss off the power company in the process of doing measurements. Although you're just minding your own business in their electromagnetic field, it could be construed as stealing power, especially when that spark plug video goes viral.

--Frank

[Mike Sokol]

On the mode of coupling, are you sure it is inductive and not capacitive? We should be able to come up with an experiment to determine this.

My sparky buddies say it's capacitive. My EE buddies say it's inductive. I'm thinking testing for leading vs lagging currents to know for sure, but my gut says inductive.

One more aside, don't piss off the power company in the process of doing measurements. Although you're just minding your own business in their electromagnetic field, it could be construed as stealing power, especially when that spark plug video goes viral.

I have my local PoCo's blessing to try this. Unofficially, of course....

[Steve M Smith]

One more aside, don't piss off the power company in the process of doing measurements. Although you're just minding your own business in their electromagnetic field, it could be construed as stealing power, especially when that spark plug video goes viral.

If they want to put an electromagnetic field into the public domain, that's their problem.

My grandfather once told me about a farmer who had a barn very close to a high power BBC transmitter.  He lit his barn with tuned circuits and small, low voltage bulbs.


Steve.

[ProSoundWeb Community]