Erico GEM

[tin2779]

Hi....

I have asked few questions about this grounding grid and it is still on going. We have decided to use Eric Ground Enhancing Meterial on the periphery of the ground grid. The ground grid is in the middle of the rock. Excavated and backfilled with granular B. I am just wondering, to acheive the full advantage of GEM it should be buried at least 2.5 ft below the grade while the grid should be 1.5 ft as per the traditional practice. I was wondering, what advantage this GEM will offer conceptually.
I would apprecaite your word.

Thanks

 

[7anoter4]

Hi tin2779
I used for many years a lot of Erico products as electrods and connectors but never GEM.
Try this link for more information.

http://www.erico.com/public/library/fep/LT0359.pdf

Best Regards

 

[jghrist]

Conceptually, the GEM around the periphery conductor will increase the effective diameter of the conductor. This will reduce the resistance to current flowing into the rock. I can see two reasons for favoring the use of GEM on the periphery conductor in particular. First, the current density is higher in the periphery conductor so you get a greater relative advantage by reducing resistance where the current is higher. Second, the periphery is where touch-potentials are usually higher. The GEM will bring the surface area around the periphery closer to that of the grid and reduce touch-potentials.

On the other hand, by reducing the relative resistance of the periphery, you may find that more of the fault current flows in the periphery than it would have without the GEM. This would negate some of the advantage but would require a detailed analysis to predict the full effect. You would have to have the ability to model the volume around the conductor at a different resistivity as the rest of the soil.