Grounding System Design

[Rock86]

I have looked at some older threads but I am hoping this gets answers with personal experience than technical data. I know this is titled "Grounding System Design", but I think it has more to do with the work leading up to the design. I am going through and designing the electrical system for a client and I have been told to refer to old drawings on a similar project.... pretty standard. But I'm looking at the grounding system previously designed and they used a triangle method with (3) 10' ground rods, 10' apart.

My questions...
* Do many of you preform ground resistivity tests prior to designing / installing / inspecting grounding systems for general commercial jobs?
* What method do you prefer?
* Do you use the results for an enhanced end game design, or just data collection?

 

[infinity]

IMO if you just use a CEE you will need nothing else (a metal watar pipe that qualifies as an electrode must be used). Think about connecting to the potentially thousands of feet of rebar encased in concrete that is contact with the earth. The old three 10' rod triangle won't add much when compared to the CEE.

 

[petersonra]

If you are only trying to comply with nec, the triangle system is not needed. It might be needed if someone is demanding it, but it is not a NEC requirement.

In any case there is no nec requirement to do ground resistivity testing at all unless your sole grounding electrode is a rod. If you plan on using a rod just pound in two of them and avoid any testing issues.

 

[Rock86]

If you are only trying to comply with nec, the triangle system is not needed. It might be needed if someone is demanding it, but it is not a NEC requirement.

In any case there is no nec requirement to do ground resistivity testing at all unless your sole grounding electrode is a rod. If you plan on using a rod just pound in two of them and avoid any testing issues.

Right, I know the NEC requirement, I was curious to see about others method for designing. grounding systems.

Now, and not to challenge or argue with you because i am in agreement, your method of pounding two rods to avoid issues... besides NEC have you ever proven there is no issue? I have no doubt that there wont be an issue... but someone at one point decided to test this and found a reason to do things differently from time to time.

 

[petersonra]

Right, I know the NEC requirement, I was curious to see about others method for designing. grounding systems.

Now, and not to challenge or argue with you because i am in agreement, your method of pounding two rods to avoid issues... besides NEC have you ever proven there is no issue? I have no doubt that there wont be an issue... but someone at one point decided to test this and found a reason to do things differently from time to time.

People paint conduit sometimes. There is no nec requirement to paint conduit.

What issue do you think there is? Suppose the soil was dry and high resistivity. How would this impact the electric system in a negative way.

 

[Rock86]

People paint conduit sometimes. There is no nec requirement to paint conduit.

What issue do you think there is? Suppose the soil was dry and high resistivity. How would this impact the electric system in a negative way.

I wasn't trying to make this thread about the positive or negative impact on a grounding system. I was asking if anyone does any testing prior to making a grounding system to justify their work.

 

[petersonra]

I wasn't trying to make this thread about the positive or negative impact on a grounding system. I was asking if anyone does any testing prior to making a grounding system to justify their work.

Why would they when such a test has little or no effect on code compliance?

 

[infinity]

Why would they when such a test has little or no effect on code compliance?

My thought as well, the NEC minimum is 2-8' rods minimum 6' apart with no testing required. Use anything better than that (like a CEE) and you've exceeded the minimum required.

 

[retirede]

I wasn't trying to make this thread about the positive or negative impact on a grounding system. I was asking if anyone does any testing prior to making a grounding system to justify their work.

As others have indicated, first of all, meet code, second, meet specs (if applicable).
There is no reason to test the GES’s relationship to dirt, since it doesn’t really do anything practical anyway.

 

[Joe.B]

There could be reasons, but it's beyond the scope of the NEC, which is what I think most of your responses are getting at. There's a big data center under construction here and their plans have a very extensive grounding ring system with hundreds of feet of big braided copper and cad welds to connect it to everything you could imagine. On top of that there's a huge lightning protection system even though we have one of the lowest rates of lightning strikes in the nation, as in never a single lightning strike recorded in my town. Obviously way way above code but the designers have their reasons for designing it this way. What those reasons are I have no idea. Like many other proprietary designs somebody probably spent a lot of money on research and they're probably not going to share it with anybody.

 

[petersonra]

Obviously way way above code but the designers have their reasons for designing it this way. What those reasons are I have no idea. Like many other proprietary designs somebody probably spent a lot of money on research and they're probably not going to share it with anybody.

I would not bet on any reason other than someone thinks it is a "good" idea. or it was done that way somewhere else. People will spend a ton of money on earthing that serves no useful purpose, but makes them think they got some benefit, but usually they cannot tell you what that benefit is.

 

[Joe.B]

I would not bet on any reason other than someone thinks it is a "good" idea. or it was done that way somewhere else. People will spend a ton of money on earthing that serves no useful purpose, but makes them think they got some benefit, but usually they cannot tell you what that benefit is.

Agreed, I wouldn't be surprised either way to be honest. There could be a body of research behind a design, but just as likely (or maybe more) that designers are shooting from the hip. If there was expensive research behind a design I doubt anybody would share it, at least not for free.