GEC protection outside structure

[Dennis]

Mike I have not used rods in a long time with new construction as I am a believer that the CEE is, without a doubt, 10 times better than a rod. A rod may help with small surges but I even doubt that. I have installed 2 rods at a site that had 89 ohms using a 3 point tester. Sane site I had a concrete encased electrode and I had 13 ohms on that-- you tell me.

 

[jwelectric]

Yes I agree that they are about as useful as dentures are for a chicken.

We played around on this little 17 acre plot with up to as many as 5 eight foot rods at a time before even getting close to 25 ohms. I have a CEE for my service and it tested over a 90 day period twice a week for an average of 7.3 ohms.

During our remodel it was good having friends with the same interest as I have and I really enjoyed the labor of love although you must know that I did not ever sweat and the pulse never exceeded 84 which means I mostly watched.

 

[ICE]

Yes I agree that they are about as useful as dentures are for a chicken.As an inspector I look at the installation to the letter of the code, which in my case is the NEC with amendments, and leave my opinion completely out of the job.

Whichever way the wind blows.

 

[jwelectric]

Which ever way the wind blows.

How much research have you done on ground rods? Any?

I don't believe any mention of code rules was involved in the question asked or the answer given by either poster. It was a direct question to one’s opinion and not a question about a code.

 

[gfretwell]

If you can get the rod down in the ground water here they work pretty well but if it is just a rod in the sand, you don't have much.

I have been involved in engineering studies on ground rods at toll booths and radio stations. Both are lightning targets and they take extra effort to get them well grounded.

Those guys were using 40' rods and radials. Although we couldn't say it out loud, the duct banks under the road were probably the best electrodes at the toll booths. They were full of steel and bonded to the GECs about 10 feet down and almost 100 feet long end to end, connecting all the booths to the admin building. They still drove 40' rods on the corners of the plaza and everything was CadWelded together with fat bonding conductors. (1/0 as I recall)

Guv'mint work. Cost was no object.

 

[jwelectric]

I spent some time at Cocoa Beach while I was in Fl. back in the early 90s watching and studying the grounding systems they were installing and the effects of a direct lightning strike on an eight foot ground rod at the Clearwater testing site.

I have done my own rod testing here on this little strip of land where I have an electric fence to contain my horses. I suppose my tests are very unprofessional but something that was needed in order to keep from chasing horses up and down the road.

My grounding system for my electric fence consists of three 10 foot rods installed in a Delta pattern and spaced 10 feet apart per the instructions. After doing several three point test on the system the average resistance was 30 plus ohms.

See this http://www.iaei.org/magazine/2011/01/grounding-resistance-and-spacing-of-ground-rods/ by the IAEI.

There is much information on the internet from many different testing labs concerning ground rods and just how useless they are during a lightning strike.

Looking closely at 250.104(A)(1) of the NEC we find that there is only four reasons that we connect our systems to earth or ground them. One of these reasons and the main reason is lightning. If the rod is not going to do an effective job of dissipating this high voltage/high current event I would think that people would be searching for something better.

 

[jwelectric]

If you have a membership IEEE has some real good stuff on ground rods.

 

[globe trekker]

jwelectric,

If you and others are so against the viability of the use of grounds, why are

they still an allowable method of grounding (by the letter) in the NEC?

Also, what do you use on "post tensioned cables" type foundations?

.

 

[jwelectric]

jwelectric,If you and others are so against the viability of the use of grounds, why are

they still an allowable method of grounding (by the letter) in the NEC?

Also, what do you use on "post tensioned cables" type foundations?

.

Don’t assume, I didn’t say that I was against anything. The codes is what they is.Any connection to earth be it an 8 foot rod or even a gutter nail is better than nothing. All I am saying is that based on the information available to anyone interested in searching there is not much difference between the 8 foot rod and the gutter nail for the purpose of the installation (lightning).

As an inspector I would be looking for either a test sheet by a licensed PE or two rods at least 6 feet apart and grass growing on top of them.

As an electrician if I can’t get to the footer before it is poured then two rods no less than 10 feet apart with at least 9 feet of depth. Got to get her low enough for the burial of the #6 going out there, right?

Look at some of the other earthing requirements found in 250.66. If we are using items such as metal water pipes (250.52(A)(1), building steel (250.52(A)(2), or even a buried oil drum in the back yard (250.52(A)(8)) we must size the grounding electrode conductor based on the SE conductors. It is possible for these three items to require a 3/0 copper conductor while the same service where none of the electrodes are found we can install two rods and a #6 copper wire.

Now I admit that I am not the brightest bulb in the fixture but the difference in current between a 3/0 and a #6 will equal an amp or two don’t you think? This makes a statement in and of itself or at least let me say it gets what little brain I have to working hard.

Other than bridges I am not very familiar with the tension cables in foundations so therefore I will stay silent.

 

[gfretwell]

"Ground" itself is a very over rated thing. I have seen spikes as big as 35-40 volts between the building steel of buildings that were very well "grounded". I think the whole concept was developed when the whole city was connected together by metal water pipes. If you are counting on dirt as your ground plane, expect wide variations from place to place.

This will become very apparent to you when you start stringing data cables between buildings.

 

[jwelectric]

No, no, no. We connect to earth not as a plane but we connect to earth for four reasons and for these four reasons only.

These reasons are outlined in 250.4(A)(1). How our systems work has nothing at all to do with the earth connection.

The earth connection has nothing at all to do with how the system operates, how good or how bad. It has nothing at all to do with clearing faults large or small.

Here are the four reasons we connect to earth

250.4 General Requirements for Grounding and Bonding.

The following general requirements identify what grounding and bonding of electrical systems are required to accomplish. The prescriptive methods contained in Article 250 shall be followed to comply with the performance requirements of this section.

(A) Grounded Systems.

(1) Electrical System Grounding. Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by

1 lightning,

2 line surges,

3 or unintentional contact with higher-voltage lines

4 and that will stabilize the voltage to earth during normal operation.

The rest of Article 250 tells us how to get this job done.

Our electrical systems will work just fine without any type of earth connection. The bonding of the EGC to the neutral in the service equipment will clear faults.

It is the earth connection requirements that cause problems with communication equipment. We have different systems operating at different frequencies that cause the problems with communication equipment.

These problems will happen if there are different communication systems with no AC power connected.

 

[Inspector 102]

On my original post, I would have had no idea that a simple question could raise such a battle between members. I apologize for any anomousities that have been displayed here. As an inspector, I have been asked more times than not "What do you want to see" by electricians. My responce is the minimum required by code or better. I do not try to place my opinion in the formula, however if asked, I might tell them minimum requirements and then how I would do it if it were my home. I basically visit this site on a daily basis and have always enjoyed the spirited comments by the members. Although I might not agree with all the statements, I consider another persons point of view or interpretation and respect that. If different than my interpretation, then I am the one that has to answer for the call and be able to back it up. Some areas have their own amendments to code issues which adds another level of opinions. As Patrick Swayze said in Roadhouse - Be Nice.

 

[gfretwell]

No, no, no. We connect to earth not as a plane but we connect to earth for four reasons and for these four reasons only.These reasons are outlined in 250.4(A)(1). How our systems work has nothing at all to do with the earth connection.

The earth connection has nothing at all to do with how the system operates, how good or how bad. It has nothing at all to do with clearing faults large or small.

That is fine as long as you have a self contained building electrical system.

You really only want to "bond" everything and provide a way to bleed off transients, although that may not happen instantly.

"Grounding" becomes a factor when you connect multiple buildings and we found the ONLY way you can trust it is to bond the buildings together with copper. I learned this the hard way at IBM and saw it in practice by someone else inspecting toll booths.

The earth may average zero volts but from point to point, you can have wide variations.

 

[karmann33]

Why be that way? You lose respect when you place yourself on high.

Lose the attitude.

You pollute the forum.

Fewer people participate when there is a jerk wad loose.

That's what I've thought reading some of your posts from time to time. Spend less time busting somebody else's nuts and try and do the best at your job and let them fail if that's what is meant to be be. Your not going to like everything that people post on here but, don't go throwing stones in glass houses. I don't post on here much because of the dipsticks on here that have negative stuff to say when you do make a comment and to that I say you know they wouldn't talk like that to you in person so why do it on here?