Bonding new counterpoise to old ones.

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Pizza_Guy

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We have a new project where we are replacing four smaller buildings with one large factory. The slabs for the existing buildings each had a counterpoise installed. The foundation for the new building will be elevated by a few inches on one side, up to a couple feet on the other, and a new slab poured on top of the old ones. We are talking about installing a new counterpoise around the new foundation for lightning protection. Any reason we can’t also bond to the existing ones?
 
OP asked 'any reason we can't bond the existing ones?', and LarryFine answered 'absolutely not'.

I read this answer as 'no reason not to bond', and I agree. There is no reason not to bond an available electrode that is present within the footprint of the new building.

One might debate the benefits of this bonding, but there is no reason not to bond.

Jon
 
winnie said:
OP asked 'any reason we can't bond the existing ones?', and LarryFine answered 'absolutely not'.

I read this answer as 'no reason not to bond', and I agree. There is no reason not to bond an available electrode that is present within the footprint of the new building.

One might debate the benefits of this bonding, but there is no reason not to bond.

Jon
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Thanks for the clarification. I read it as “absolutely not” to bind them together, lol
 
Pizza Guy, you got me curious. Counterpoise has a few different meanings depending on context. What are you calling a counterpoise, and how is it used?
 
Good question… yeah, I think the last engineer and I have different definitions of “counterpoise”, lol.

for me, I intend to install a ground ring around the entire building foundation. Other engineering firms I worked at call that a “counterpoise”. The other engineer I am replacing says the existing buildings have a counterpoise. But, I think he is referring to a “delta ground”, or what I learned to call a grounding triad. For full disclosure, the existing buildings were always meant to be temporary, and do not have a LPS.

either way, I’m not entirely sure what to expect under the ground, but I’ll install a grounding ring anyway
 
Pizza_Guy said:
I intend to install a ground ring around the entire building foundation.
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OK, that I understand. At first, I thought this might be a critical mission communication facility like I work with. FWIW it is a Ground Ring. A counterpoise is an artificial ground that takes the place of earth, like the frame and chassis of a ship, plane, or auto usually associated with antennas. Sometimes called a ground plane.

Ground Rings are very effective ground electrodes when integrated with LPS. Every radio tower and critical mission facility uses them; at least every site I have built uses them. I worked for Ma Bell, MCI/Worldcom, and VZW for a couple of decades as a Power Protection Engineer. Be warned they can also cause a lot of damage if misused. Ground Rings are utilized for LPS; they are not suitable for Medium and High Voltage applications.

Twenty or so years ago, I did mission work for my church in India in a few villages. For decades the villagers suffered many injuries and fatalities from nearby lightning strikes. The grass huts and shelters have bare dirt floors; when lightning strikes nearby trees, the Step Potential created by lightning injures and kills the occupants. I knew from my Internship at Disney Parks in Orlando back in the late '70s and early '80s during the construction phase of the park; a Ground Ring was the answer. Disney has the best LPS in the world and is one of the pioneers of LPS. The only problem is where to get the wire to construct the ground rings. We used fence wire, baling wire, old abandoned telephone wire, or whatever we could get out hands-on.

When lightning enters the earth, it discharges by spreading outward along the surface like a wave in a pond when you chunk rock in it. That creates the Step-Potential difference, about 1000 to 2000 volts per linear foot. Distance between your feet is enough to kill. A Ground Ring intercepts and shunts the current around the protected area and is highly effective if it is shallow, roughly 6-inches deep. Yeah, I know the NEC requires the ring to be buried deeper; do not count it as an electrode to keep the inspector happy.

However, if misused can cause significant damage. The one thing you never want to do, I am a broken record here, only bond the ring to the facility to at one point where the AC Service enters. If you bond at two different locations, you will create a ground loop providing a direct path for lightning to come inside and have dinner on you and exit violently, making a mess of things inside.

So if you have an existing ring, use it. Just open it up, add the new concrete pad, and close the ring with a wire. FWIW use solid copper, bare tinned, copper #6 AWG wire.
 
Just to expand so I understand. BOND at one point at Service Entrance. I've noticed some drawings call out a ring or additional grounding but do not specify bonding to Service. without bonding you could create a step potential. correct me if I am wrong
 
keith gigabyte said:
Just to expand so I understand. BOND at one point at Service Entrance. I've noticed some drawings call out a ring or additional grounding but do not specify bonding to Service. without bonding you could create a step potential. correct me if I am wrong
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You have it correct. Just keep a simple rule of thumb in mind. Bond everything below-grade together to form a common ground electrode system—bond to the GES at one location only. Bond twice, and you place the facility between two ground electrodes, which will force common-mode currents to flow, and if there is lightning will flow through the facility.

Keep in mind for current to flow, it has to have a point (node) of entry and a point to exit.
 
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