Supplemental grounding electrodes, such as rods, pipes, or plates, must meet the 25-ohm requirement specified in NEC Section 250. For galvanized steel and hollow sections of GI (Galvanized Iron) pipes, suitable sizes are 0. For instance, in the US, the National Electrical Code (NEC) requires that ground rods be driven at least 8 feet. But, there are four variables that affect the ground resistance of a ground system: Single ground electrode. Minimum Contact: A rod electrode must have a minimum of 8 feet of its length in direct contact with the soil.
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