Why should a pole down ground not be the sole connection when grounding a line?

A pole down ground may not be reliable as the sole grounding connection because it could fuse under fault current conditions. When a fault occurs, a significant amount of current can flow through the grounding system. If the current exceeds the thermal limit of the grounding conductor, it can cause the conductor to heat up and potentially melt or fuse. This can create a dangerous situation where the grounding connection becomes ineffective, leaving the equipment and personnel unprotected from electrical faults.

While the other options address various limitations or concerns, they do not capture the critical aspect of the integrity of the grounding system under high fault conditions. A dependable grounding system must be capable of safely handling fault currents without compromising its effectiveness, ensuring proper functionality in emergency situations.