How many ground rods?

I suspect that the changes @hillbilly1 made helped his customers. However I am of the opinion that the bonding was the primary reason for the improvements, and the ground rods secondary at best.

I've had one experience where ground rods without bonding apparently caused a problem. Service entrance with ground rods on one side of the building, Telco demark with its own ground rod on the other side of the building. No bonding between them.

No evidence of external damage, but a section of phone wire inside the building looked like a Christmas decoration. Every few inches there was a jagged copper spike sticking out of the wire, with a single mark on the wood behind it.
 
winnie said:
I suspect that the changes @hillbilly1 made helped his customers. However I am of the opinion that the bonding was the primary reason for the improvements, and the ground rods secondary at best.

I've had one experience where ground rods without bonding apparently caused a problem. Service entrance with ground rods on one side of the building, Telco demark with its own ground rod on the other side of the building. No bonding between them.

No evidence of external damage, but a section of phone wire inside the building looked like a Christmas decoration. Every few inches there was a jagged copper spike sticking out of the wire, with a single mark on the wood behind it.
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Isn't it possible to have more grounding make things worse? With a lightning event, you can have ground potential rise, and it seems logical that the "better" grounding you have than the more of that rise your electronics will see.
 
electrofelon said:
Isn't it possible to have more grounding make things worse? With a lightning event, you can have ground potential rise, and it seems logical that the "better" grounding you have than the more of that rise your electronics will see.
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With sufficient bonding I don't see ground rods hurting, because everything will experience the same elevated voltage.

But if you don't have bonding IMHO more ground rods would make things worse. In the example I saw, perhaps not having the telephone company ground rod would actually be safer.
 
winnie said:
I suspect that the changes @hillbilly1 made helped his customers. However I am of the opinion that the bonding was the primary reason for the improvements, and the ground rods secondary at best.

I've had one experience where ground rods without bonding apparently caused a problem. Service entrance with ground rods on one side of the building, Telco demark with its own ground rod on the other side of the building. No bonding between them.

No evidence of external damage, but a section of phone wire inside the building looked like a Christmas decoration. Every few inches there was a jagged copper spike sticking out of the wire, with a single mark on the wood behind it.
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The one below the rock quarry the bonding issue was a major component, but the others were not bonding issues.
 
winnie said:
With sufficient bonding I don't see ground rods hurting, because everything will experience the same elevated voltage.

But if you don't have bonding IMHO more ground rods would make things worse. In the example I saw, perhaps not having the telephone company ground rod would actually be safer.
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My thinking is the number of different scenarios are numerous. For example, is lightning traveling on one of the conductors (and if so which one), or is it a ground potential rise issue. If so, what is the relative location of the building ground and the ground referencing the electrical system. are there multiple electrodes, where are they relative to the ground potential rise. Is the voltage of the electrical system between conductors still the same it is just the ground potential has risen? Just lots of different scenarios and I can envision situations where the more electrodes and more grounding you have, you are going to see more of that ground potential rise and get more damage to equipment.
 
electrofelon said:
So with all the grounding on the line, probably hundreds of ground rods (depending on how big an area we want to bring into it of course). You think a couple more is going to make any difference? Also if the lighting hits the ungrounded conductor, which is usually on top and more likely I would think, more grounding of the neutral isn't going to change anything.
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I directed the installation of over 200 remote communications shelters to Motorola Standard R56 - Standards and Guidelines for Communication Sites. [No the US National Electric Code (NEC) is not the do all and end all of everything electric and electronic. Imagine that.] I never lost operational time to a lightning strike and in radio communications height is might. You site the shelters on the highest bit of real estate that you can get the use of. Lightning strikes to the towers with attendant side flashes to the shelter and dozens of conductors for many different purposes passing from things outside the shelter to things inside the shelter are not rare.

In general the objective was a Grounding Electrode System with an impedance to earth of 10 Ohms or less. In a couple of cases that was achieved with shallow trenches in the rock of a ridge with a six inch wide copper strap running for 50 feet with Bentonite clay over and under the strap and then capped with moisture stable concrete. It's a lot of effort but it works. Many such shelters function for decades problem free.

I'm one of the few electricians I ever heard of who personally owned a Grounding System Impedance Tester. [OK I'm a tool whore.] I used it on every single service construction or change out. I own a Milwaukee electric demolition hammer and the bit I used in it most was a Ground Rod Driving Cup. Unless the customer had decided to do without the additional protection, since with me it was strictly optional, I would hit a maximum of 50 Ohms. When the customer declined the additional work I always took the few minutes it required to explain the lightning damage exclusion that I then added to our agreement,

I regularly put in he the Grounding Electrode System which was developed by the then National Bureau of Standards which is now the National Institute of Standards and Technology, which consists of 2 driven rods 20 feet apart and then driven within a couple of inches of the bottom of a 30 inch trench. The Grounding Electrode Conductor (GEC) was #4 bare copper or a continuous run of bare copper #2 AWG for both the bonding conductor and the GEC. Whenever feasible I kept the rods their own length away from basement walls or other in ground structures. You may recognize these lengths as the minimum requirements for a ground ring and a driven rod electrode. I have no idea if that was intentional on the part of the NBS researchers but it sure avoids disputes over grounding with the electrical inspectors. If the impedance was still over 50 Ohms to ground I would stack another rod onto each of the first 2. I kept drive on couplings on the van so that I could use the regular 8 foot long rods. While my customers neighbors were filing claims against their power utility my customers were enjoying a trouble free electrical installation.

By the way in many of the areas I've worked in the primary distribution conductors have arrestors on them at the places were those ground rods are. Certainly not universally true but often enough that I would think it somewhat common.
 
electrofelon said:
Isn't it possible to have more grounding make things worse? With a lightning event, you can have ground potential rise, and it seems logical that the "better" grounding you have than the more of that rise your electronics will see.
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Not according to the National Institute of Standards and Technology (NIST). See their publication "Getting to Earth."

The situation that winnie encountered is a very common cause of lightning damage in an electrical installation. When the return stroke of a lightning discharge strikes the earth a voltage gradient occurs across the surface of the earth from the discharge point outward. The differences between points only several feet apart can be extremely high. As the area the lightning is dissipating through gets larger the voltage falls off to zero. The part of a second during which all that happens subjects everything the discharge passes to extremely high voltage differences which force destructive current flows through electrical wiring and electronic loads. Non bonded electrodes will bring their different voltages to devices which are connected to both systems, such as the computer's power supply and its network card. Everything in between those 2 disparate voltages is likely to be damaged in the absence of effective equalization devices. Surge suppressors work by shunting the current driven by the higher voltage to the conductors having the lower voltage. They do not actually arrest anything. The make them close enough to equal that there is not enough difference of potential between them to drive a destructive current flow.
 
roger said:
I don't know about the OP's situation but the ball field lighting I have done had anywhere from 12' to 30' deep 24" to 36" diameter pole bases loaded with rebar, it's doubtful a few rods would make any difference.
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The utility installed some steel poles for a 138kV line. The poles had a concrete base about 8' in diameter, 25' deep. It had 1" vertical rebar on 12" centers about 18" in from the outside, and 3/4" horizontal rebar rings on 8" centers, with the 15 or so anchor bolts attached to the rebar cage. They still install a 10' ground rod with 4AWG to the steel pole!
 
hillbilly1 said:
You can’t say ground rods are absolutely worthless, I’ve had several jobs where they had lightning issues, and adding ground rods and proper bonding solved the problem. I have a neighbor that lives on top of a hill that all pasture, no trees. His fence charger got knocked out every time a storm came up. Installed two rods at the barn, two at the house, and two at the utility pole feeding the house. He hasn’t replaced a charger since. Another customer had a house below a rock quarry, lightning constantly taking out his tv and telephones. The phones and cable drops were at the opposite end of the house from the service, and were not bonded to the service. Added a rod at both ends, and buried a #4 bare copper between them. He hasn’t had a problem since.
Another customer was at the end of the poco line, and was constantly getting surges during storms. Added three rods, and problem stopped.
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Surge protector at the service equipment may have solved those issues as well.
 
electrofelon said:
. What does that mean?



So with all the grounding on the line, probably hundreds of ground rods (depending on how big an area we want to bring into it of course). You think a couple more is going to make any difference? Also if the lighting hits the ungrounded conductor, which is usually on top and more likely I would think, more grounding of the neutral isn't going to change anything.
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If you have a rather direct hit, you are screwed, if it strikes nearby, like a pole a quarter mile away, any rods between you and the strike are absorbing some the energy, if you happen to have surge protection it hopefully minimizes the effects within your premises wiring.
 
kwired said:
Surge protector at the service equipment may have solved those issues as well.
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This was back before surge protectors were common place. None were installed at those locations. Next week putting one in at a poultry transport facility, wood building with metal roof and siding. They said they had a ground rod drove at each corner, but I haven’t seen how they are connected yet. They claim lightning runs along the conduits and out of the outlets.
 
infinity said:
I agree. The client doesn't know any better that's why they hired professionals to do the design in the first place. We did a huge apartment building with probably 2000 linear feet of footings with CEE's. They also had us install at least ten of the 3/4"X10' triangle rod nonsense with grounding test wells in the basement. Talk about a waste of money.
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Those test wellls will never be opened once you terminate them.
 
hornetd said:
Not according to the National Institute of Standards and Technology (NIST). See their publication "Getting to Earth."
.
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I still stand by my belief that there are many different scenarios and you just can't just generalize and say that more or better grounding will will result in a better outcome. Which conductor has the surge or strike (grounded or ungrounded)? is the distribution system an MGN or Delta?? If it's an undergrounded system, where is the system earthed? Is it Earthed in multiple locations? How far are the multiple earthing locations apart and from the structure served? This all will affect ground potential rise and where that ground potential rise is. And I think a lot of stuff in that communications/Motorola standard or whatever is hogwash, , like most grounding information.
 
kwired said:
I don't necessarily buy that. One time incident maybe but not something that happens more than one time.
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I’m kinda suspicious of it too, there are two grain silos next to the building on a different service, and they say they’ve had no problems there. I have no doubt the conduits are not complete, and have romex pulled into them. I haven’t opened up the panel yet to see what kind of nightmare it is. The silos are newer, and looked like they were professionally done. I know it wasn’t a local because it’s all in rigid and looks good!
 
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