What is the maximum allowable resistance reading for a 3-point fall-of-potential earth resistance test?

The correct answer is based on the standards set for achieving safe grounding practices, especially in electrical and explosive environments. A 3-point fall-of-potential earth resistance test is crucial for determining whether a grounding system has an adequate level of resistance to facilitate safe electrical operations.

A maximum allowable resistance of 25 ohms is established to ensure effective grounding. This limit helps to reduce the risk of electrical shock and ensures that in the event of a fault, any excess current can be safely dissipated into the ground. Ground resistance higher than this threshold may not effectively protect personnel and equipment from potential hazards.

Establishing a maximum threshold of 25 ohms ensures proper operation of protective devices and minimizes the chances of ground potential rise during fault conditions, which can be critical in preventing accidents in environments with explosive materials. It aligns with safety standards that prioritize the reliability of grounding systems to protect both human safety and sensitive equipment.