Is a ground grid a fault return path

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dbursheim

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The following question has to do with grounding/earthing and bonding in industrial plants where an interconnecting ground grid is installed in the earth and foundations to encompass all conductive surfaces of the entire facility.
The contractor in accordance with the project specifications is to provide complete bonding of all raceways to the equipment and to the cable trays to provide an effective ground/earth fault return path. The construction engineers are maintaining that there is more than adequate fault return path because of the amount of interconnected bare ground copper wire in the ground grid. This ground grid connects to the frames of all electrically connected equipment and is connected to the cabinets and ground/earth busses of all low and medium voltage equipment.
If what they are saying is true, then I will stand corrected and stop insisting on a good bonding system. If what they are saying is incorrect, where is a good source of training material that I can get to help the engineers understand?
This is not an uncommon problem on the international projects that I have worked.
 
dbursheim said:
If what they are saying is true, then I will stand corrected and stop insisting on a good bonding system.
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The way you are using the terms is confusing me a little.

Is what you are "insisting on" that the measured resistance between the "ground grid" and the planet Earth be as low as possible?
 
From what I can grasp from your post.

You have a ground grid that covers the complete plant? This includes the grid is bonded to all structural steel?

You are insisting on a copper EGC that is to be bonded to the raceway at each end?

1. EMT by itself when properly installed is an effective GF return path. And is all that is required by the NEC.

2. Anything you add to that is a benefit. Is there a cost ratio benefit to more copper, more bonding, more labor VS time to operate an OCP?

3. Who wrote the specs. and what do they say?

Think about this, If what I posted regarding the structural steel being bonded to the grid, then the EMT is mounted to the structural steel plus all the air, water, fluid piping and metal ducts all are connected to the structural steel, plus if there are anchors in the concrete that hit the rebar. You have large fault return path, then if you also have an copper EGC installed properly, you have a decent GF return path.

But if you have the power to add to it that is your call I would think?
 
Your equipment bonding conductor (whether just a metal raceway, or a wire within it) must usually follow the path of its associated conductors (NEC 300.3). A jumper from a piece of equipment to a ground grid isn't following that path.

So you must properly bond the metal raceways segments to each other and to the equipment. There's nothing wrong with supplemental bonding to a ground grid, or augmenting a metal raceway with a separate bonding wire within the raceway, or using a bonding locknut on a raceway that doesn't require one.
 
In a couple of the larger industrial plants in this area, they have for years relied on the "grid" system for their grounding/bonding. The facilities are mostly 480v un-grounded systems with the feeders run on open insulators. The feeders are tapped with EMT/weatherhead runs to overcurrent devices mounted on the steel columns. Each building has ground ring attached to each column and to the supply transformers and distribution gear.
For years there has been an ongoing war that this was not "Code" but the "always been" and politics have prevailed.
 
The lack of a "neutral" (functioning as a ground) in the onsite distribution voltage resulted in another "distribution voltage neutral" carrying a certain voltage which only appeared when certain equipment was in operation. This unusual voltage potential was unknown to the JW and apprentice working on the equipment. Nevertheless, they tested the grounded conductor for voltage and found none. It was later determined that this intermittent voltage killed the apprentice as his JW watched. An appropriate and code required "ground" as the POCO guys would call it, run with the ungrounded conductors would have saved this guy's life and he would still be with his wife and young child.
 
iMuse97 said:
The lack of a "neutral" (functioning as a ground) in the onsite distribution voltage resulted in another "distribution voltage neutral" carrying a certain voltage which only appeared when certain equipment was in operation. This unusual voltage potential was unknown to the JW and apprentice working on the equipment. Nevertheless, they tested the grounded conductor for voltage and found none. It was later determined that this intermittent voltage killed the apprentice as his JW watched. An appropriate and code required "ground" as the POCO guys would call it, run with the ungrounded conductors would have saved this guy's life and he would still be with his wife and young child.
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I am not sure what you are saying and/or how this applies to the OP's question.
 
dbursheim said:
The following question has to do with grounding/earthing and bonding in industrial plants where an interconnecting ground grid is installed in the earth and foundations to encompass all conductive surfaces of the entire facility.
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If this is what the job is spec'd for or if this is what the owner wants then why even have the following sentence to have an arguement about
The contractor in accordance with the project specifications is to provide complete bonding of all raceways to the equipment and to the cable trays to provide an effective ground/earth fault return path. The construction engineers are maintaining that there is more than adequate fault return path because of the amount of interconnected bare ground copper wire in the ground grid. .
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...

They don't want to do it, they don't undertand it, they want an out?
They sure don't seem so business wise in today's hand holding world... ;)

This ground grid connects to the frames of all electrically connected equipment and is connected to the cabinets and ground/earth busses of all low and medium voltage equipment.
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Think of the Grid and let me give a example that you have a ringed building or even a small apron around a building, or even without a ring or grid. With all things considered or spec'd, with a totally bonded structure hasn't it just insured no possible potienal difference within that space, and to the objects in the structure, etc, etc.

It's sudo inexpensive, expensive and can be real expensive to do some of these things, got to have the grounding, the bonding well that can go the various ways of expensive as well.
 
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dbursheim said:
The following question has to do with grounding/earthing and bonding in industrial plants where an interconnecting ground grid is installed in the earth and foundations to encompass all conductive surfaces of the entire facility.
The contractor in accordance with the project specifications is to provide complete bonding of all raceways to the equipment and to the cable trays to provide an effective ground/earth fault return path. The construction engineers are maintaining that there is more than adequate fault return path because of the amount of interconnected bare ground copper wire in the ground grid. This ground grid connects to the frames of all electrically connected equipment and is connected to the cabinets and ground/earth busses of all low and medium voltage equipment.
If what they are saying is true, then I will stand corrected and stop insisting on a good bonding system. If what they are saying is incorrect, where is a good source of training material that I can get to help the engineers understand?
This is not an uncommon problem on the international projects that I have worked.
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The Engineers already understand this and that is why they are engineers by definition. Improper grounding techniques are doomed from the start. Listen to the electrical engineers this is their training.
 
brian john said:
I am not sure what you are saying and/or how this applies to the OP's question.
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The op stated grounding/earthing /bonding and he is obviously disturbed about a faulty bond to the wrong system which resulted in death. Have a little compasion for his concern. They obviously knew they had an intermitten problem which should not have been worked on by an apprentice level electrician. Apprentices have NO place in a powerplant. In my strong humble opinion.
 
quogueelectric said:
The Engineers already understand this and that is why they are engineers by definition. Improper grounding techniques are doomed from the start. Listen to the electrical engineers this is their training.
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I think he is referring to construction engineers (not EEs), and that term itself may actually be loosely applied given the location of the construction site.
 
quogueelectric said:
The op stated grounding/earthing /bonding and he is obviously disturbed about a faulty bond to the wrong system which resulted in death. Have a little compasion for his concern. They obviously knew they had an intermitten problem which should not have been worked on by an apprentice level electrician. Apprentices have NO place in a powerplant. In my strong humble opinion.
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Thanks for the defense of my concerns. However, I can see how BJ was confused. To deal with two issues:
1. The bonding of systems and equipment grounding is crucial to the safety of all the systems in a very large facility. This seems to be the issue of the OP. In my post, I intended to describe how one guy recently got killed on the manufacturing premises of a Fortune 100 company because of poor bonding practices and poor maintenance of the distribution system. His death illustrates the importance of the bonding and grounding in such a facility.

2. As to the apprentice on this job: he was one of the sharper knives in the drawer and just a great guy, and he and the journeyman had taken all precautions required (as you can imagine, this was investigated at great length and expense). He was killed by the messenger wire, which carried intermittent voltage on it only when certain equipment in another area of the plant was operating under specified conditions.
 
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iMuse97 said:
I think he is referring to construction engineers (not EEs), and that term itself may actually be loosely applied given the location of the construction site.
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I have worked in a few powerplants for short intense terms which tested the limits of my knowledge there is a lot of politics i these plants which even adds more fuel to the fire yet there was always at least a half dozen EEs on site who directly tweaked day to day events. I was always the engineers go to guy which caused hard feelings with the local and plant electricians . Someone who is a construction manager or not formally trained is not going to just run in and school the engineers of thier knowledge. The tail does not wag the dog.
 
iMuse97 said:
...
1. The bonding of systems and equipment grounding is crucial to the safety of all the systems in a very large facility. This seems to be the issue of the OP. In my post, I intended to describe how one guy recently got killed on the manufacturing premises of a Fortune 100 company because of poor bonding practices and poor maintenance of the distribution system. His death illustrates the importance of the bonding and grounding in such a facility.

...
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I don't see that incident as a bonding incident. It resulted from working on an energized circuit. Additional bonding or grounding on the load side of the system or main bonding jumper may or may not have prevented the death, and could create other hazards.
 
don_resqcapt19 said:
I don't see that incident as a bonding incident. It resulted from working on an energized circuit. Additional bonding or grounding on the load side of the system or main bonding jumper may or may not have prevented the death, and could create other hazards.
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I'll see if I can get specific info. re: the determination of cause. And O.P., are you still here?
 
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