Ground Grid Design
Ground Grid Design
(OP)
If any of you do ground grid design, I'm just curious how you treat the top layer of soil during winter conditions.
I can't find any definitive information on how to treat the soil and the extent to which the soil freezing affects resistivity.
All indications are that the resistivity will go up by about 300% (at a minimum) and the freezing depth will depend on geographical location.
Can anyone offer any guidance on this?
I can't find any definitive information on how to treat the soil and the extent to which the soil freezing affects resistivity.
All indications are that the resistivity will go up by about 300% (at a minimum) and the freezing depth will depend on geographical location.
Can anyone offer any guidance on this?






RE: Ground Grid Design
On the other hand, the fusing characteristics of the grounding conductors favor to withstand better SC during frozen conditions since both, conductor resistance is reduced helping to generate less heat by Joule effect and the lower ambient temperature help to the heat transfer of the conductor.
Therefore, the worst-case scenario does not happen during the coldest season.
RE: Ground Grid Design
RE: Ground Grid Design
I doubt that there would be a real big effect. The grid is normally installed about 1.5 feet below grade. The frost line in northern USA is 3-4 feet, so there is only 1.5-2.5 feet of frozen soil between the grid and the unfrozen soil.
You could measure the soil resistivity during a hard frost and use a soil model with an extra layer representing the frozen soil. SES grounding software allows you to specify the depth of a layer when calculating layer resisistivities from test data. You could then analyze a grid both with and without frozen soil to see what difference there is in touch potentials. If you do, please publish your results.
RE: Ground Grid Design