Ground Ring

[stickboy1375]

250.52 Grounding Electrodes
(A)(4) Ground Ring

A ground ring encircling the building or structure, in direct contact with the earth , consisting of at least 20' of bare copper conductor not smaller than 2 AWG...

okay here is my question, everytime my boss installs one of these, he only installs the 20' of copper, but the code says "encircling the building" any opinions? And of course we have 2 ground rods as well...

 

[infinity]

According to the wording of the article the ring needs to encircle the structure. If the structure were say a pole than 20' of conductor would need to encircle that pole to qualify as a ground ring. The ground ring needs to be minimum of 20' in length but not shorter than required to encircle the structure. If you have two ground rods you don't need the ground ring at all.

 

[stickboy1375]

According to the wording of the article the ring needs to encircle the structure. If the structure were say a pole than 20' of conductor would need to encircle that pole to qualify as a ground ring. The ground ring needs to be minimum of 20' in length but not shorter than required to encircle the structure. If you have two ground rods you don't need the ground ring at all.

I know I don't need the ground ring if two rods are installed, looking at a lightning point of view...

 

[infinity]

I know I don't need the ground ring if two rods are installed, looking at a lightning point of view...

I'm not sure which is more effective. The ground ring buried at 30" or the rods down to 8' below the ground.

 

[acrwc10]

All the Ground rings I have installed were #2 tinned copper buried min. 24" , with a 10'x5/8" rod cad welded to the ring ever 10'.They circled the building.This was an engineered design for tele-com. site. I look at them as an under ground fence that will intercept and divert any transiant current through the earth. If your site is between a utility transformer ground rod and a fault being feed by that transformer, the fault will follow the path of least resistance which could be the building structure or the equiptment in your building.

 

[George Stolz]

acrwc10, Faults do not seek the path of least resistance. They seek any path back to their source.

Stick, according to a report that Bryan (BPHgravity) read and shared with us a while back, one of the most effective lightning configurations is a ground rod with conductors tied to the top of it, at an angle into the earth. (Picture an arrow pointing upward.)

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I guess this follows the lightning's natural path, fanning out once it has struck the earth.

 

[acrwc10]

, Faults do not seek the path of least resistance. They seek any path back to their source.

They will still seek that path through the least resistance. that would be the reason for the ring to encircle the building not go in a 20' line near it.

 

[stickboy1375]

, Faults do not seek the path of least resistance. They seek any path back to their source.

They will still seek that path through the least resistance. that would be the reason for the ring to encircle the building not go in a 20' line near it.

Actually they seek EVERY PATH back... and you cannot use ground rings, rods, etc to clear a fault, the ground resistance is so high it would never trip the OCP.

 

[George Stolz]

Stick, he's referring to a slightly different perspective. The electrode we're looking at is a spectator to the fault from a distance. It is not doing the fault clearing. It's standing in the middle of the "road" watching traffic.

That said, the current/voltage this electrode sees should not last long if it is a fault condition; the lion's share of fault current should be travelling through the effective ground fault current path at that remote service, opening the OCPD there, and very short in duration.

 

[George Stolz]

They will still seek that path through the least resistance.

Would you say that the current seeks all paths in proportion to their resistance?

that would be the reason for the ring to encircle the building not go in a 20' line near it.

I am not an expert on this topic, but I wonder if perhaps in this case the location of the electrode is more (or as) important as it's resistance and stats.

However, I would say these aspects are moot when 250.4(A)(1) is taken into perspective. For the NEC's purposes, I would think a straight line is peachy keen, IMO.

 

[dereckbc]

I design and test quite a few ground rings in telephone facilities, so I might be able to clear up some misconceptions.

First a ground ring is not designed to clear any electrical fault from the AC distribution system, which is forbidden by the NEC and a mute point.

The ground ring is used for 3 main reasons.

• To provide relative voltage free reference point.
• Easy access to the ground electrode system from multiple points on the buildings perimeter. Telephone offices have multiple cable entrances like commercial power, outside cable plant, and coaxes/waveguides from towers. At these points surge arrestors need direct access to earth for maximum effectiveness.
• Quick and safe discharge path for outside faults like lightning.

 

[George Stolz]

Thanks, Dereck!

 

[bphgravity]

One theory is the voltage divide method which requires the use of a ground ring or counterpoise. Imagine ten down conductors or radials connected to a ground ring. Lightning current from a single strike termination point would likely be divided up into ten smaller segments. This will help insure that the lightning will more likely follow the designated paths for dissipation into the earth and lower the resulting ground potential rise to the adjacent equipment building grounding system.