An electrode that does not have a resistance to ground of ___ ohms or less shall be augmented by one additional electrode.

An electrode that does not have a resistance to ground of ___ ohms or less shall be augmented by one additional electrode.

• A. 6 ohms
• B. 25 ohms
• C. 30 ohms
• D. 20 ohms

Answer: (C)

Grounding systems need a low impedance path to the earth so fault currents can return quickly and trip protective devices. When a single grounding electrode has too high a resistance to ground, the code requires adding another electrode to bring the overall impedance down. In this item, the threshold used is 30 ohms. If an electrode measures more than 30 ohms to ground, it must be augmented with one additional electrode. That’s why 30 ohms is the correct fill-in — it marks the point at which adding another electrode is required to improve the grounding system’s performance. The other values would not indicate the trigger point for augmentation in this version of the rule.

Grounding systems need a low impedance path to the earth so fault currents can return quickly and trip protective devices. When a single grounding electrode has too high a resistance to ground, the code requires adding another electrode to bring the overall impedance down.

In this item, the threshold used is 30 ohms. If an electrode measures more than 30 ohms to ground, it must be augmented with one additional electrode. That’s why 30 ohms is the correct fill-in — it marks the point at which adding another electrode is required to improve the grounding system’s performance. The other values would not indicate the trigger point for augmentation in this version of the rule.