Grounding Questions

Your local standards code dictate what you must do.

Beyond that, I am with #1 all the way. Terminally, one point grounding.

Think about it this way: you have a lightning system with its separate ground. Then a lightning hits. Its separate ground lifts a million volts, temporarily. As it dissipates, other grounds of yours get lifted by some amounts.

You tell me, what happens to your electronics get lifted by a fraction of a million volts, while other parts do not? I hope you do not expect a happy outcome?!?

Hire a qualified electrician.

Lightning protection system should have at least 2 down conductors and earth points.

Actually, lightning does differ from country to country due to altitude, air pressures, humidity etc. It is also dependant on soil types and soil structures, i.e iorn ore deposits, other metals that may be found in the ground. And of course structures on the ground surface that may attract lightinng by giving off streamers.

But in reply to the question, all earths need to be bonded together, increased spacing and surge arrestors, may be required on/for critical circuits.

Does a body of water nearby will attract lighting?.

Lightning always finds the least path of resistance to ground. Lightning does not strike the ground, a steamer rises from any upright object, i.e person, giraffe, tree, building, pole, mast etc. If the resistance to a streamer is low, that item will be struck, but streamers may emanate from any of the items. If the object is a tree around the water edge, then it could be struck and the water will disipate the charge. If a sail boat is out on the water, the mast acts as as a lightning rod, a streamer will emanate from the mast top and it will be struck, but a low lying puddle, pond, lake etc would in all probability be too low and many streamers would appear across the water surface. It is what is around the body of water that would be struck. Lightning strikes occur at sea frequently. The most common misnomer about lightning.......you can assume, but never predict where it will strike.

You can attract it to strike a certain place or point, but it is not always the rule. It follows the least path of resistance and that means air flow changes the path.

Lightning does strike the ground in some cases. The main stroke of lightning will touch the path of least resistance in full force at some point...it doesn't just stop short of the intended path when a leader rises to meet it.

The leaders set the path of least resistance which the stroke(s) will follow.

It is more likely to be attracted to a nearby tree.

Dear Mr.bib,

The answer for your quiery

1. No. It should be independent.

2. No. Plant grid should not be linked.

3. No. Two seperate earth is better option.

DHAYANADHAN.S

Can you offer back up on the statements pleas? I am intrigued by this but I assume you have a valid point. I am not to sure what it is or why, but I am interested in this point. I look forward to your explanation. Thanks.

Re: Question 1--The plethora of documentation held at various national levels stating that lightning and protective grounding systems shall be bonded provides more than enough evidence to state that the OP should do so. The IS which I have access to, however, reserves section 8 and does not address specifically the issue. Using an out such as not being regulated by one agency, and saying one could do otherwise just because one agency didn't say no is not a good reason to proceed with that plan. It is not prudent.

However, even regarding the IS for questions 2 & 3:

Whether using TN, TT, or IT systems...the intent is to keep the impedance between exposed parts as low as reasonably achievable. If not it is necessary to provide local equipotential bonding for an entire installation or a part thereof, an item of apparatus or a location. IS:3043-1987 18.0.10

Within a particular part of a zone where extraneous conductive partsare simultaneously accessible with either other extraneous conductive parts or exposed conductive parts or both...it is necessary to carry out local equipotential bonding between the parts concerned in order to obtain satisfactory low impedance. IS: 3043-1987 18.3.4

The somewhat weakly-worded and short-sighted (frankly, short) IS may not address the situation specifically, but the derived meaning is still there. If exposed parts are acessible at any one point they must share a common bond. Personnel safety prevails over operations.

Dear Mr. Pete, Even though Section 8 of IS 3043 does not address much on Lightning Protection, there is a specific IS (IS 2309 - Code of Practice for the protection of buildings & structures against lightning), which specifically states that the lightning protection grounding system MUST be bonded to all other plant services earthing. This also substantiates what you have mentioned too.

Yes, I found those rules with a bit more searching. They are now in my library and next on my reading list.

1. I am from India and my country Standard on Lightning Protection says that the Lightning Protection Grounding System and the all the plant services grounding system MUST be interconnected (vide IS 2309)

2. Vide IEEE 1100, the electronic equipment grounding MUST be bonded to the system grounding.

3. Vide the Indian Electricity Rules, 1956, there shall be two separate and distinct connections with two independent earth electrodes for neutral.

The above are what is practiced in India. You may refer to your relevant country codes.

1. Are you referring to clause no. 12.3.3 of IS:2309 ? You are right. Though, it does not specifically mention grounding grid. And IS:3043 does not specifically mention any such bonding.

2. I think you are referring to Cl. 8.5 of IEEE:1100. Again there is no specific mention of the same in any IS. And the instrument vendors insist for independent ground grid.

3. Your clarification is OK. However, I asked if the two independent earth electrodes are to be bonded to the plant earth grid or not. From all the standards I understand that the same is to be bonded to the plant earth grid. However, again there is no specific mention of the same in any IS or IE Rules. And electrical inspectors define it differently.

Also I wanted to know is there any technical advantage if I connect the neutral first to the independent earth electrode and then connect the earth electrode to the plant grid.

Sorry if I am late.

BS6651/1999 Code of practice for protection of structures against lightning

"17.3 Common network for all services

A common earth termination network is recommended for the lightning protection system and all other services. It should be in accordance with the recommendations of this code of practice and should also comply with any regulations applicable to the services concerned. The resistance to earth should, in this case, be the lowest value needed for any of the individual services."[BS6651 recommends 10 ohm for lightning protection grounding].

NFPA-780/2004

"4.14 Common Grounding.

4.14.1 General. All grounding media in or on a structure shall be interconnected to provide a common ground potential.

4.14.1.1 This interconnection shall include lightning protection, electric service, telephone, and antenna system grounds, as well as underground metallic piping systems."

In my opinion, the lightning strike current flows perpendicularly to the Earth surface towards the Earth depth. A conductor laying parallel with the surface will present a large reactance and in a few feet almost no current will flow towards the outside. In order to equalizing the outside potential with inside potential both grounding systems have to be bonded together.

Well, that pretty much covers most of the civilized world.