To insure that electric supply facilities comply with the rules of the National Electrical Safety Code (NESC), Rule 214A 2 states, “Lines and equipment shall be inspected at such intervals as experience has shown to be necessary.” What does this mean? How frequent is “…intervals as experience has shown to be necessary”? To understand this rule, we need to talk about the limitations of inspection in identifying NESC violations and averting electrical contact accidents.
The materials used to construct electric supply facilities deteriorate over time. Deterioration of these materials can create violations of the NESC and hazards to the public. Metal enclosures like electric meter sockets located in salt fog environments typically near ocean beaches often corrode to the point of developing holes. The following photograph is an example of violation and hazard created by a corroded steel electric meter socket. The socket was located about a hundred feet off an ocean beach. The socket was still energized when I took the picture and was located only three feet off a sidewalk where hundreds of people walk to the beach every day. The holes in the enclosure did not develop overnight. If the utility who owned the socket found from experience that it takes a minimum of four years for holes to develop after the initial signs of corrosion, then it would be appropriate for that utility to inspect their steel meter sockets located in that environment at least every four years as long as they replaced the sockets showing signs of corrosion within the four-year period after inspection.
The strength of wood utility poles deteriorate with time. The structure loading and strength requirements of the NESC in Sections 25 and 26 define when a pole shall be replaced. When considering ice and wind loading of Rule 250B and using the overload factors of Table 253-1 and the strength factors of Table 261-1A, the NESC in footnote 2 of Table 261-1A (page 182) requires wood poles to be replaced or rehabilitated when deterioration reduces the structure strength to 2/3 that required when installed. When considering the extreme wind loading of Rule 250C, footnote 3 of Table 261-1A requires wood poles to be replaced or rehabilitated when deterioration reduces the structure strength to ¾ that required when installed. Allowing pole strength to deteriorate below the minimum set by the NESC not only creates a violation of the rules, it also creates hazard to the public if the pole breaks. Some utilities and contractors have developed non-destructive test methods for predicting the strength of wood poles in the field. These methods can be used to identify poles for which the strength has deteriorated. If a utility tests its poles and replaces deteriorated poles on a eight-year cycle and finds that they experience very few pole failures under anticipated loading conditions, then experience has shown that an eight-year pole inspection cycle is appropriate.
Electrical Contact Accidents
Most electric supply contact accidents involving the public are not a result of anything to do with deterioration of the utilities facilities. Most accidents involving electric utility facilities are the result of people working too close or constructing buildings and other structures too close to energized conductors. Constructing buildings and other structures so close to electric supply facilities that the clearance between the building and the line is less than that required by Rule 234 (page 96) of the NESC is a clear violation of the rules of the NESC and a hazard to the construction and maintenance personnel. One would think that the OSHA regulations and the fear of electrocution would stop people from approaching electric power lines. That is not enough.
In an attempt to stop the fatalities, most states have now made it illegal to approach high voltage electric power lines. Those laws are usually called “High Voltage Line Safety Acts.” To learn more about these laws and the OSHA regulations, see my March/April 2000 article, “Working in Dangerous Proximity to Overhead High Voltage Lines—OSHA, NESC, and the Law.” Even with the OSHA regulations and the state laws, the dangerous actions continue. The brick masons who decide to re-point the brick building with a metal aerial lift, the sign company who decides to install a new store sign directly beneath the power line, the painters who decide to paint a house with aluminum ladders crossing under the power line, the industrial plant that decides it needs to construct a large storage tank under the power line, the house builder who decides to build a house under a power line, are all examples of the types of accidents that occur on a daily basis around the country.
Would regular scheduled inspections catch these situations? No, not unless they were very lucky. That is not to say that none is averted by utility employees while they are doing other work. Most utilities have a lot of employees in the field on weekdays. Often these employees, police officers and people from the public do catch dangerous actions before they become fatal ones. It is this type of inspection the NESC is referring to in the note following Rule 214A 2, “”It is recognized that inspections may be performed in a separate operation or while performing other duties, as desired.”” Most utilities encourage their field employees to look for dangerous conditions and actions by the public. That does not mean that every utility employee in the field has the time or the knowledge to recognize a dangerous condition or action. There are some electric utility employees that have no more knowledge of the hazards associated with electric power lines than the general public. It is unreasonable to expect all electric utility employees to be responsible for identifying dangerous actions and conditions.