Distribution Pole Inspections and the Impact on Electric System Reliability

Frequency and Process of Wood Pole Inspection

The typical wood pole inspection program involves inspecting 10 percent of an electric utility’s poles in a given year (i.e., poles are inspected on a ten-year cycle). These inspections are conducted using utility personnel or more commonly a specialty service contractor. Some inspection programs are the result of mandated programs in some jurisdictions; others are part of elective periodic maintenance programs. Each pole inspection involves an examination of the pole for possible ground line and/or pole-top rot.

The method may involve “sounding” (i.e., hitting the pole with a hammer-like tool to detect hollowness) or boring into the wood and taking a sample. If the inspection determines that a pole has lost too much of its inner core to be structurally sound (Figure 1), it is marked for replacement or reinforcement.

Reliability or Liability

Pole rot is rarely a cause of electric service outages, having no significant impact on average electric system reliability statistics. Even when in-line poles are hit by a vehicle and broken at the base, they usually hang from the wires and a pole that is completely rotted will not necessarily fall over unless other external forces are applied to it. Should a pole fall, it will most likely break the conductor (i.e. the equivalent of a large tree branch falling on a line).

Therefore, the main reasons for inspecting and replacing (as necessary) wood poles are two-fold:

• Preserve (in the long-run) the health and condition of its assets
• Avoid liability for negligence should a pole fall (even if hit by a vehicle) and injure someone.

The risk of a single $1 million-dollar lawsuit can justify a significant pole inspection and replacement program (approximately $25 per inspection and $2,000 per replacement).