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Author Topic: Temporary grounding  (Read 5219 times)

Stephen Swaffer

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Temporary grounding
« on: April 01, 2016, 10:24:47 pm »

There have been past threads discussing temporary grounding methods.  The president of the local ham club and a POCO employee told me about this-which they (I guess us since I am getting involved) use for their temporary generator setups during field days:

http://www.jharlen.com/hasfib4370.html

Not sure how the inspectors would view a 6 ft rod vs an 8 ft-but I thought I saw something arguing that the screw threads added contact area?  Certainly better than nothing.

Not cheap-but maybe cheaper than a chiropractor or doctor visit from driving a rod and pulling it.

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Tim McCulloch

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Re: Temporary grounding
« Reply #1 on: April 01, 2016, 10:40:32 pm »

There have been past threads discussing temporary grounding methods.  The president of the local ham club and a POCO employee told me about this-which they (I guess us since I am getting involved) use for their temporary generator setups during field days:

http://www.jharlen.com/hasfib4370.html

Not sure how the inspectors would view a 6 ft rod vs an 8 ft-but I thought I saw something arguing that the screw threads added contact area?  Certainly better than nothing.

Not cheap-but maybe cheaper than a chiropractor or doctor visit from driving a rod and pulling it.

The augur screw ground rod comes in a couple of different flavors, IIRC, but it's common kit on lineman's bucket trucks.

For pulling conventional ground rods I've seen a fence post puller used.

Ask yourself "what would a farmer do?"  ;)
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Lyle Williams

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Re: Temporary grounding
« Reply #2 on: April 01, 2016, 11:39:50 pm »

Ground rods are cheap.  It's easier to keep driving them than to pull them.
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Lee Buckalew

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Re: Temporary grounding
« Reply #3 on: April 02, 2016, 12:50:20 am »

Ground rods are cheap.  It's easier to keep driving them than to pull them.

When I was doing festivals we would dig a hole before driving the ground rod then drive the rod in the hole.  Didn't need to be super deep but it let us drive the rod and simply disconnect from it and backfill the hole when we were done. 

Lee
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Mike Sokol

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Re: Temporary grounding
« Reply #4 on: April 02, 2016, 08:29:12 am »

When I was doing festivals we would dig a hole before driving the ground rod then drive the rod in the hole.  Didn't need to be super deep but it let us drive the rod and simply disconnect from it and backfill the hole when we were done. 

Lee

I've just begun experiments with my bed-o-nails ground plate design. Basically, this uses a dozen or more 12" landscape spikes through a common plate. Since these spikes will penetrate the ground less than a foot, they should be well above the 18" minimum buried depth of water pipes and underground wiring in my part of the country. And they're a lot easier to pull out of the ground compared to an 8 ft ground rod. I think you could pound in a dozen or so 12" spikes and dump a gallon of water on this grounding plate for a good temporary ground. However, I need to run a fall of potential test on my prototype unit to see how well it really works before I suggest it as a possibility. And it will need to be documented to even have a chance of passing an inspection. 
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Frank DeWitt

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Re: Temporary grounding
« Reply #5 on: April 02, 2016, 01:32:17 pm »

Ask yourself "what would a farmer do?"  ;)

Always good advise but be advised, it often involves welding.
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John Roberts {JR}

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Re: Temporary grounding
« Reply #6 on: April 02, 2016, 05:05:16 pm »

I expect results may depend on how deep the local water table is. In my yard the 12" spikes would be fine and probably rust away but I can imagine geographies where 12" may still be in the relatively dry surface zone.

A bunch of short spike in parallel only works equivalent if the soil is the same conductivity near the surface and deeper. 

FWIW the spikes don't need to be large diameter (acupuncture needles), but that is likely determined by the mechanical stresses to punch through several feet of dirt. 

JR
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Mike Sokol

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Re: Temporary grounding
« Reply #7 on: April 02, 2016, 05:47:51 pm »

A bunch of short spike in parallel only works equivalent if the soil is the same conductivity near the surface and deeper. 

The plan would be to use this as a temp generator ground for a few days at most. And the dirt around it could be kept wet by dumping a gallon of water on it every day. I get a little worried when I see someone driving an 8-ft ground rod with possible underground pipes and wires.

I've got all the parts, I just need to assemble it and take some fall-of-potential measurements. An 8-ft ground rod will typically measure around 25 ohms impedance if it's in decent shape in conductive soil, and up to 100 ohms if the soil is really dry. It will be interesting to see exactly what impedance a dozen 12" spikes in wet ground will have.   

I'm going to try galvanized landscape spikes first since they're designed to be driven into the dirt, and cost less than a buck a piece. I've got a simple holder designed that will bond them all together and let you lever the spikes out of the dirt when the show is finished.

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Frank Koenig

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Re: Temporary grounding
« Reply #8 on: April 03, 2016, 12:45:27 pm »

I've just begun experiments with my bed-o-nails ground plate design.

Another thing to consider when pounding 8 or 10 ft. ground rods into every city park, corporate parking lot, or back yard where you have a gig is what it might hit under ground. Maybe you just bust the sprinkler system or maybe you puncture a gas line and take out a city block. (Gas can flow along the outside of a damaged pipe and into confined spaces.) So, I agree, once it's in leave it there for next year's event, but a shallow grounding solution sounds very attractive to avoid this risk.

Best,

--Frank
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Lyle Williams

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Re: Temporary grounding
« Reply #9 on: April 03, 2016, 04:39:56 pm »

Always good advise but be advised, it often involves welding.

I went to an accident where a fire truck had rolled off the side of a country road into a creek (it was on it's side in the water.)  When the dozer turned up I thought it was going to make a mess of the truck pulling it back up the hill.

The dozer driver proceeded to shift the level of the roadway down to the fire truck, and then flip the truck neatly back on it's wheels.

Farmers think in ways mere mortals can't.  Farmers can also do things that mortal's can't.

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John Roberts {JR}

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Re: Temporary grounding
« Reply #10 on: April 03, 2016, 05:23:29 pm »

Another thing to consider when pounding 8 or 10 ft. ground rods into every city park, corporate parking lot, or back yard where you have a gig is what it might hit under ground. Maybe you just bust the sprinkler system or maybe you puncture a gas line and take out a city block. (Gas can flow along the outside of a damaged pipe and into confined spaces.) So, I agree, once it's in leave it there for next year's event, but a shallow grounding solution sounds very attractive to avoid this risk.

Best,

--Frank
Funny a few years ago when I had my home's water mains pipe replaced, the plumber used manual labor to dig the trench, because to use a machine digger he would have to file for permission with the utilities and perhaps weeks of delay before my water was restored.
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Fast forward to about a month ago a contractor (working for the power company) that was dropping in some new light poles to add lights around a town jogging/walking track, placed one new pole smack in the middle of the town water main.. We had dirty water for a few days.

Seems they should have known better. I busted the power company worker I knew (from playing basketball with him), and he blamed it on the sub contractor.  :o

JR
   
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Ike Zimbel

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Re: Temporary grounding
« Reply #11 on: April 03, 2016, 07:28:10 pm »

The plan would be to use this as a temp generator ground for a few days at most. And the dirt around it could be kept wet by dumping a gallon of water on it every day. I get a little worried when I see someone driving an 8-ft ground rod with possible underground pipes and wires.


True story: I did an outdoor festival once, in Montreal, which was set in the parking lot of a race track. Due to a scheduling "thing" we didn't get the PA until the morning of the event, and when we finally got that flown and powered up, not long before our noon start time, it was humming and buzzing like mad. Long story short, when we finally tracked down where the generator was grounded, we found that the providers had just jammed the ground rod in a pile of gravel back stage. I had someone go and pour a bottle of water on the ground rod and you could actually hear the gurgling and splashing of the water as it modulated the ground noise in the PA. Problem was solved when the ground was tied to an existing ground rod at the base of a lamp standard...which was right next to the pile of gravel!
iz
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Dennis Wiggins

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Re: Temporary grounding
« Reply #12 on: April 03, 2016, 08:00:29 pm »

...An 8-ft ground rod will typically measure around 25 ohms impedance if it's in decent shape in conductive soil, and up to 100 ohms if the soil is really dry. It will be interesting to see exactly what impedance a dozen 12" spikes in wet ground will have.   

25-100 Ohms between the ground rod and what?  I know that sounds like a dumb question, but is it to a known good POCO ground?

-Dennis
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Frank DeWitt

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Re: Temporary grounding
« Reply #13 on: April 03, 2016, 08:37:25 pm »

I went to an accident where a fire truck had rolled off the side of a country road into a creek (it was on it's side in the water.)  When the dozer turned up I thought it was going to make a mess of the truck pulling it back up the hill.

The dozer driver proceeded to shift the level of the roadway down to the fire truck, and then flip the truck neatly back on it's wheels.

Farmers think in ways mere mortals can't.  Farmers can also do things that mortal's can't.

It was a farmer, not an engineer who figured out how to make a hay baler tie a knot.  Think about it.  How would you make a machine tie a knot.   I also have a video of two red necks (related to farmers) working together to lift a big antique generator onto a low boy truck.  One was driving a tree picker used for logging and the other a oversized tow truck.  Each one lifted one side and that generator went straight up with not so much as a wiggle. Backed the low boy trailer under it and they set it down just as nice.
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Mike Sokol

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Re: Temporary grounding
« Reply #14 on: April 03, 2016, 08:38:30 pm »

25-100 Ohms between the ground rod and what?  I know that sounds like a dumb question, but is it to a known good POCO ground?

-Dennis

Great question. There's two ways to measure this. The most common way is something called a fall of potential test. Basically, you drive a second short ground rod some 100 ft away from the ground rod under test. Then a known current is induced between the test rod and the ground rod. A third test rod is put in the earth between the other two rods. This one measures the voltage drop as its moved between the two other rods at 10 ft intervals. Sounds more complicated than it is, but it does take some time to do properly, and the ground rod under test needs to be disconnected from any building grounds. Basically you need to take voltage measurements at measured intervals to make sure it graphis as a proper S-Curve. Then you can calculate the ground rod impedance. See first diagram below. A "Fall of Potential" tester costs around $500 or so. I've got a B&K one on my desk.

The second type of tester uses a high frequency current in a special type of clamp-meter to inject current into the ground rod under test while it's tied into the POCO's grounding grid. So it compares the impedance of your single ground rod to all the millions of other ground rods on the bottom of power poles. These testers cost around $1,500 or so and I've been begging for one, but still no go. That's what I want to use to test my Bed-O-Nails design since it doesn't require all the graphing work.

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Lee Buckalew

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Re: Temporary grounding
« Reply #15 on: April 03, 2016, 08:40:47 pm »

Another thing to consider when pounding 8 or 10 ft. ground rods into every city park, corporate parking lot, or back yard where you have a gig is what it might hit under ground. Maybe you just bust the sprinkler system or maybe you puncture a gas line and take out a city block. (Gas can flow along the outside of a damaged pipe and into confined spaces.) So, I agree, once it's in leave it there for next year's event, but a shallow grounding solution sounds very attractive to avoid this risk.

Best,

--Frank

Yes, we always had the stage site set up for utilities locate and also confirmed if we could leave a rod in place.

Lee
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Mike Sokol

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Re: Temporary grounding
« Reply #16 on: April 03, 2016, 08:44:18 pm »

Yes, we always had the stage site set up for utilities locate and also confirmed if we could leave a rod in place.

Lee

Yup, you really don't want to be driving in 8 ft ground rods without the Utilities giving you the all clear.
« Last Edit: April 03, 2016, 10:36:45 pm by Mike Sokol »
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Mike Sokol
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Re: Temporary grounding
« Reply #16 on: April 03, 2016, 08:44:18 pm »


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