The grounding survey team needs to be experienced with different types of grounding applications and have a firm understanding of relevant codes and standards. Otherwise, the ground system survey may not result in the optimal recommendations. Ground system resistance requirements should be interpreted for different facilities by different standards.
One standard doesn’t fit all applications or facilities ground resistance requirments. A review of the facilities environment and requirements will determine the standard applied.
For example, NEC article 250.56 requires a 25-ohm ground system resistance with the installation of a single ground electrode for any service entrance electrical system to protect against electrical hazards. It also states that an additional single electrode should be installed if the goal resistance is not met. Thus, NEC safety requirement may be satisfied by the installation of two (2) electrodes, resulting in a much higher resistance than 25 ohms.
However, for critical microprocessor based instrumentation or other power quality sensitive applications, this resistance may not be sufficient. Additionally, grounding and bonding requirements for flammable operations may differ from standard electrical codes. Grounding system resistance for high voltage applications should be low enough to meet step-and-touch safety voltage criteria per IEEE-80 standard.