In 1993, a homeowner in Pennsylvania was standing on a ladder preparing to paint the fascia of his house just below the roof. His right hand, holding a wire brush with a metal scraper at the end of the handle, contacted an uninsulated clamp that spliced a 120-volt service drop conductor of a triplex cable to a conductor of the house’s service entrance cable. He received an electrical shock, shook his arm in an effort to break the circuit, fell from the ladder and was severely injured.

Within the dwelling, there were many examples of where an occupant could with impunity grasp a conductor energized at the same voltage. An appliance power cord being plugged into an energized outlet is the prevalent example. The low-voltage insulation covering the indoor conductors, when in good condition, ensures the safety of the occupant. In principle, the same insulation safeguard against electrical shock should have been provided at the junctures of the service drop and service entrance conductors.

The triplex service drop cable, consisting of two energized and one grounded conductor, was the property of the electrical utility, while the service entrance cable, attached to the house, was the home owner’s property. The triplex service drop cable originated at the low-voltage windings of a pole-mounted primary distribution transformer, but could have also been connected to a secondary distribution feeder. Service drops and secondary distribution feeders were generally of the open-wire type until about the mid-1990s.

With improvements in polymeric materials for electrical applications, the energized and grounded neutral conductors could be covered with long-life, reliable insulation that allowed them to be wrapped around each other indefinitely without short-circuiting.

Since the house had been built shortly after 1959, the 1959 National Electrical Code (NEC) was applicable. It addresses requirements for service drops and states at Rule 230-4 that “Service conductors shall have an insulating covering which will normally...prevent any detrimental leakage of current to adjacent...objects.” But the NEC also states at Rule 90-2(b) that, “It [the NEC] does not cover installations...employed by...electric utility in the exercise of its function as a utility...” The National Electrical Safety Code (NESC), to which electrical utilities generally conform, does not specifically address requirements for service drops. Electrical utility companies do not permit outsiders except contracted electrical personnel to handle, install or maintain their equipment.

Nevertheless, utilities’ employment of adequate coverings on their service drop conductors is not completely discretionary. Utilities are not free to arbitrarily set up their own installation and maintenance procedures without regard to industry practice and public safety. Thus, the electrical utility was responsible for installing the service drop conductors between its distribution transformer and a mechanical clamping arrangement. This included a weatherhead on its customer’s premises, splicing them to the customer’s service entrance cable and in accordance with good engineering practice, insulating the connectors using either preformed insulators or tape. NEC Rule 110-14, Splices required that, “All splices and joints...of conductors shall be covered with an insulation equivalent to that on the conductors.”

Similarly, NESC Rule 316, Splicing and Taping, required that “...joints of insulated conductors...shall have equal insulating covering with other portions of the conductor...”

The NESC generally required inspections by company personnel, (i.e., at Rule 213A5, Inspections of Lines When in Service, “Defective lines and equipment shall be put in good order or effectively disconnected.”) Meter readers are frequently instructed to note and report conditions such as missing insulation. This employee requirement for reporting defects appears in NESC Rule 420B as follows, “An employee shall report as soon as practicable to his superior...any obvious hazards observed...in connection with any electrical...lines.” A power consumption meter was mounted in this case on the same wall as the weatherhead. Lack of insulation, which had been missing from the connector for several years, was obvious without resorting to binoculars or a bucket truck. In fact, the house probably had an open wire service drop when first constructed. It could be concluded that at a later date, when a changeover to triplex cable was being accomplished, insulation over the splices had been neglected.

In addition, the NESC Rules, notably 200C, 202, 210 and 211 of the 1948 Edition, are often interpreted to provide safety factors that reflect foreseeable activities by members of the public near an electrical utility’s facilities. Thus, the electrical utility had sufficient guidance to enable it to install and maintain its service drop and splices to its customers’ service entrance conductors in a well-insulated and safe condition. EC

MAZER is a consulting electrical engineer who specializes in electrical safety issues. His telephone number is 202.338.0669, and his e-mail address is [email protected].