The Case of the Murderous Motor

DN Staff

April 4, 2005

4 Min Read
The Case of the Murderous Motor

Around the Great Lakes in Chicagoland where my office is, the cold wintry winds are known as the "hawk." For me, an attorney's call on a new case promised a trip to Florida's gulf side, an escape from the "hawk's" claws and a chance to catch some rays.

Scene of the Crime

A maintenance electrician was repairing an HVAC unit on the rooftop of a condo buildling. When he failed to return home that evening, his worried family alerted his employer. The employer found the electrician sprawled over the open top of the HVAC unit, fatally shocked.

The family of the deceased sued, naming several defendants including the contractor that installed the HVAC unit. That contractor's attorney retained me to determine what caused the fatality. A new unit had been installed and the faulty HVAC unit was sequestered for examination. Inspection commenced with other parties to the suit present.

The Investigation

Burn marks on the technician's forearm and abdomen indicated the current path. The torso burn mark matched the position of the edge of the open top, and established the electrical ground point, but not the source of current entry into his forearm.

The mystery here was the lack of any open, unguarded, live electrical terminals in the space where the technician was working. This space was taken by two fan motors that blew cooling air over condenser units. Electrical schematics showed these two motors were supplied with 440V, three-phase ac. One or both units would operate depending on the level of cooling required. One condenser fan motor was not close enough to have been touched by the technician. And since all of the wires going to it were intact, I excluded it as a current source.

I found a ground wire from the other fan motor that had been sliced through with the cut end close to the motor. This wire was bolted to the HVAC frame, its solid ground connection proven by a continuity test. Considering that the wire was grounded, I excluded it as a current source, but I was concerned about this lack of a connection. A ground wire provides a safe, needed path to ground for any leakage or fault currents. In this case, if one of the power leads should touch the motor frame, or if an internal winding should break down, the resulting fault current would then safely blow a fuse or open an overcurrent circuit breaker.

The power leads to the motor were disconnected and measurements were made to each of the motor windings. I found a low-resistance path from one of the windings to the frame of the motor. As a quality touch, the motor was mounted on rubber antivibration motor mounts. These mounts mechanically isolated the motor, but coincidentally, electrically isolated the motor. With the ground wire cut, the electrical fault left this motor sitting with its frame at a lethal 440V potential.

Drawing of the motor circuit.

Fingering the Culprit

A comparison of the motor location and the position of the technician's body confirmed the motor was the source of the fatal current, but left a new mystery of who cut the wire and why?

The cut ground wire was removed for microscopic and metallurgical analysis. The met lab confirmed that the wire had been cut by a plier-type side cutter, but the oxide present indicated that the cut was not recent. This seemed to exonerate the deceased technician, but the fingers now pointed to the contractor for whom I worked. He claimed, and records showed, that he made service calls right after installation-the last some two years prior to this accident. A review of the condo service records revealed that a building "handyman" had replaced the condenser fan motor in question. My opinion was that the handyman cut the ground wire from the motor he removed, but didn't reinstall the ground wire on the new motor which subsequently failed. I prepared an opinion report and gave a deposition in this case. I later learned that my client was let out of the suit by a summary judgment of dismissal.

Thoughtless sins of omission or commission can be more dangerous than we realize.

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