Question
I am modeling a substation grounding system using MALT where there is a control building which has a concrete floor. After running MALT, it shows the maximum acceptable touch potential is exceeded inside the building. Can we assume the concrete floor is an isolated layer? Should we be concerned about the touch voltage problem for this area even though it has a concrete floor? Why?
Answer
It is usually not a good assumption to consider concrete as an isolating material. Unless it is treated with special chemicals, concrete will absorb water from its surroundings and become substantially conductive. However, if there is rebar embedded in the concrete, then the entire concrete area can be considered an equipotential. If the rebar is connected to the grounding grid, then the concrete area can be ignored for the purpose of safety calculations.
Therefore, it is quite important to determine if there is rebar in the concrete and, if so, if it is connected to the grounding grid. If not, the safest thing to assume is to ignore the presence of the concrete altogether.
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