A single electrode consisting of a rod, pipe, or plate that does not have a resistance to ground of ___ or less shall be augmented by one additional electrode.

A single electrode consisting of a rod, pipe, or plate that does not have a resistance to ground of ___ or less shall be augmented by one additional electrode.

• A. 6 ohms
• B. 6 volts
• C. 25 ohms
• D. 25 volts

Answer: (C)

Grounding systems aim for a low-impedance path to earth so fault current can quickly trip protective devices. For a single electrode—whether a rod, pipe, or plate—the allowable resistance to ground is 25 ohms. If the measured resistance to earth from that single electrode is higher than 25 ohms, you must add an additional electrode to create another path to earth and lower the overall impedance of the grounding system. This is why 25 ohms is the threshold used in practice. The other options mix units or values that aren’t the standard limit for this rule (ohms are a measure of resistance, while volts measure potential).

Grounding systems aim for a low-impedance path to earth so fault current can quickly trip protective devices. For a single electrode—whether a rod, pipe, or plate—the allowable resistance to ground is 25 ohms. If the measured resistance to earth from that single electrode is higher than 25 ohms, you must add an additional electrode to create another path to earth and lower the overall impedance of the grounding system. This is why 25 ohms is the threshold used in practice. The other options mix units or values that aren’t the standard limit for this rule (ohms are a measure of resistance, while volts measure potential).