In July 1982, an embassy building was under construction in Washington, D.C. A stainless steel handrail was under construction adjacent to and above a sloping garage entrance.

A journeyman ironworker was operating a portable ¼-inch electric drill in connection with the handrail installation. It was a heavy-duty ¼-inch industrial drill, with a 6- to 8-foot power cord, terminating in a three-prong plug. The plug had been inserted into the receptacle of a 100-foot-long extension cord, which was lying on the ground and owned by the ironworks subcontractor.

The plug was inserted into one of six receptacles installed in a connector body of another 100-foot extension cord, which was also on the ground. It was owned by a masonry subcontractor doing terrazzo finishing in front of the building.

The plug of this second extension cord was in turn plugged into one of four receptacles installed in a box that was temporarily affixed to a wall within the embassy. Finally, a 30-foot-long cable ran from this receptacle box along the floor to a panel box installed in the corner of a room on the main floor. No ground fault circuit interrupters (GFCIs) were present in the feeder circuit supplying power to the portable drill.

The ironworker was holding the portable drill while drilling one of several holes in a dowel pin. He was attempting to make adjustments to a pre-assembled rail fence so that it could be installed in accordance with specifications.

He was kneeling on one knee, grasping a metal fence post with his left hand, while holding the electric drill with his right hand. While the drill bit was in a hole in the post, he began to experience a severe electric shock. Sweating profusely, he managed to release his left hand from the metal post, and to remove the drill bit from contact with the post.

However, he was unable to loosen his right hand grip on the drill handle. Finally, he stood, took several steps away from the extension cord, dove onto his shoulder, and rolled over, thereby pulling the plug out.

Co-workers had been shocked earlier while standing on wet grass operating this drill. After the accident, tests established that there was no continuity in the grounding conductor path of the 30-foot length of cable into which the first 100-foot-long extension cord was plugged. Also, two receptacles in the extension cord’s connector body were not grounded.

However, the absence of a continuous grounding connection between the metal body of the portable electrical drill and the ground at the service panel was not enough to cause an electric shock. Additional defects could be present in the feeder circuit, or in the tool itself.

Because no one was shocked while operating other portable equipment on the same feeder, it was concluded that an intermittent fault in the portable drill had caused the 120-volt supply voltage to be present on its metal body at the time of the accident. It was also concluded that the feeder circuit was defective, and the involved equipment was unavailable for my testing or inspection.

The severe electric shock resulted from departures from good installation practice, and lack of conformance to the following NEC and OSHA Rules and Regulations that were in effect.

The energized state of the portable electric drill. The energized state of the noncurrent-carrying part of the drill violated Rule 110-7 of the 1978 NEC. Other employees were shocked previously while operating the same drill on the same feeder. Failure to perform inspections to determine the causes also violated OSHA Rule 1910.303(b).

Lack of a continuous grounding path.

NEC Rule 250-45(d) and OSHA Rules 1910.304(f)(4) and 1910(f)(5)(v) required continuous paths connecting the noncurrent-carrying parts of portable electrical tools to ground. OSHA also required an assured grounding program, at Rule 1910.304(b)(ii)(1) if GFCIs were not in use. If such a continuous grounding path had existed, the electrical potential of the drill body would have been reduced to zero or to a low, harmless, possibly imperceptible level.

Lack of a ground fault circuit interrupter (GFCI).

This had been required for many years by NEC Rule 210(8)(b) and OSHA Rule 1910.304(b)(i)(1). They were readily and inexpensively available for installation at construction sites.

NEC Article 305 covered basic requirements for temporary electrical installations. The strict requirements imposed on permanent installations were somewhat relaxed for temporary ones, per NEC Rule 305-1. Nonetheless, the general contractor was responsible for safe temporary power being made available to all subcontractors. (See NEC Rule 90-1(a).)

The use of short lengths of extension cords by tradesman tapping off a temporary feeder is understandable, but 200 feet of ungrounded extension cords lying on the ground, serving as the main temporary power feeder, was unacceptable and hazardous. (See NEC Rule 305-2(b).) The associated additional grounding impedance is addressed in NEC Rule 110-10.

MAZER is a consulting electrical engineer who currently specializes in electrical safety issues. His telephone number is (202) 338-0669, and his e-mail address is wmmazer@aol.com.