There is one written item that really affects designing, installing and monitoring for the optimal quality of supply (which also means minimal power quality problems). It is Article 250.56, which reads, "Resistance of Rod, Pipe, and Plate electrodes. A single electrode consisting a rod, pipe, or plate that does not have resistance to ground of 25 ohms or less . all be augmented by one additional ode of any of the types specified by 250.52(A)(2) through (A)(7).? The 25-ohm number has been taken further by some organizations to state much lower numbers, including, "the installation manual of the ground must be less than 1 ohm the reference section." This is missing reason for the original requirement, which was not intended to improve the quality of the supply but rather to provide adequate low-impedance path for fault current to flow, which would allow for the overcurrent circuit protection (breakers fuses) to trip and clear the fault quickly.
MIL- HDBK-419A and others indicate that 10 ohms is the maximum for adequate lightning protection, while the Institute of Electrical and Electronics Engineers (IEEE) Std. 141 (The Red Book) points to a 5-ohm recommendation.
