"Ground Ring" or "Delta Ground"

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djcrzysounds@yahoo.com

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Scranton, Pa
I'm unsure of the terminology, when you drive 3 rods in a triangular configuration and connect it with 4/0 (Exothermically connected). And with that being said when do you use that as opposed to 1-2 ground rods or even a ground ring?
 
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bphgravity

Senior Member
Location
Florida
I'll be honest and say I have no clue where the origin of the triangular ground rod configuration came from. I can tell you it really doesn't serve any purpose, at least, not so great that the benefits verses another configuration would ever be noticable or documentable.

I believe the intent is to create ONE large electrode out of three rather crappy individual electrodes. Once the total surface area in contact with the earth + calculating in the "sphere of influence" + the typical longer rods used in this cofiguration = lower earth resistance. (Not that any of that really matters all that much)

I'm sure there is some creative math and physics to the whole idea, but when all is said and done, none of it really matters all the much.

Theoretically, if you want to create a grounding system out of three ground rods which would positively be more effective than any "code permitted" configuration, you could do something like this:

Lay the three ground rods in 24" deep trenches so the middle rod is 180? perpendicular to the service / structure. The other two rods angled somewhere around 45? in realtion to the middle rod. Run a #6 AWG to the middle rod and bond the other two rods.

This would probably give you the best possible grounding configuration for use with a LPS and will be more than sufficient for any other typical service grounding.
 
dereckbc

dereckbc

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Staff member
Location
Plano, TX
I think I can shine a little light on the so called Delta Ground. It has some other names like Triad and Crows Foot. It stems from terminating lightning protection systems down conductors to earth in a fashion that reduces the inductive properties of the ground rods.

First consider a single ground rod in soil. When lightning strikes are delivered to a ground rod, the rod will be surface charged to a calculable velocity factor. Expressed as E = L di/dt where di is the lightning strike peak current, and dt is the rise time.

There is a limitation created by a length of a single ground rod as it penetrates it way through the relatively high resistance near the surface area of the ground rod and works to lower resistance to more conductive soil at the lower depths of the rod. So in effect this inductance of the top portion of the rod in higher resistance and CHOKES OFF current flow to the more conductive soil deeper down along the lower depths of the rod. This produces a large voltage drop along the more inductive top portion of the rod. When this occurs there will be saturation and local ground potential rise due to this breakdown.

So one solution is to use more than 1 ground rod and add parallel circuits to reduce the inductance. One such method is a Triad, (aka Delta or Crows Foot)
 
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djcrzysounds@yahoo.com

Member
Location
Scranton, Pa
dereckbc said:
I think I can shine a little light on the so called Delta Ground. It has some other names like Triad and Crows Foot. It stems from terminating lightning protection systems down conductors to earth in a fashion that reduces the inductive properties of the ground rods.

First consider a single ground rod in soil. When lightning strikes are delivered to a ground rod, the rod will be surface charged to a calculable velocity factor. Expressed as E = L di/dt where di is the lightning strike peak current, and dt is the rise time.

There is a limitation created by a length of a single ground rod as it penetrates it way through the relatively high resistance near the surface area of the ground rod and works to lower resistance to more conductive soil at the lower depths of the rod. So in effect this inductance of the top portion of the rod in higher resistance and CHOKES OFF current flow to the more conductive soil deeper down along the lower depths of the rod. This produces a large voltage drop along the more inductive top portion of the rod. When this occurs there will be saturation and local ground potential rise due to this breakdown.

So one solution is to use more than 1 ground rod and add parallel circuits to reduce the inductance. One such method is a Triad, (aka Delta or Crows Foot)
Click to expand...

Makes sense. However, where in the NEC does it say anything about it? I've been looking now for 2 days and haven't seen anything about it.
 
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