CORRECTION: The following article incorrectly states that conduit is not permitted to be used as an equipment-grounding conductor. The NEC does allow continuous electrical metallic tubing (EMT) to serve as an equipment-grounding conductor. In addition, the so-called “screw in hook” is actually an approved conduit drive strap, which you initially drive in place with a hammer. EC&M regrets the error.
While searching with a maintenance electrician for the source of arcing in the attic of a bank in eastern Pennsylvania, an alarm technician sat down on a wood floor joist and stabilized himself by briefly grasping a portion of thin wall conduit that entered the bank from the north side of the building. As he did so, his body tensed up and then jerked. The electrician pulled the alarm technician free from the conduit, but he was already dead.
In his report, the county coroner noted a small burn mark on the alarm technician's left palm and a somewhat larger burn mark on the inside of his left thigh. The cause of death was determined to be electrocution, but the coroner contacted me and requested that I determine how it happened. As I looked into the case, the evidence began to suggest a pattern of improper installation and dismantling procedures that were ultimately responsible for the accident.
The investigation. I began my investigation with an interview of the bank's maintenance electrician. He told me he arrived at the bank after the alarm technician had advised the bank management of arcing and sparking in the attic. When the electrician arrived, the technician showed him the location of the sparking. It was at that time the technician sat on one of the wood support joists and began to seize.
From there, my investigation moved on to the building itself. The alarm technician was wearing long pants while working in the attic, so the burn on the inside of his left thigh was curious. Photo 1 shows the area in the attic of the bank where the electrocution occurred. A thin wall conduit ran alongside the joist at the area where the alarm technician had placed his left leg. When I examined how the thin wall conduit was attached to the side of the floor joist, I observed that whoever installed the conduit did not use a proper conduit clamp. Instead, the conduit was held in place with a screw-in hook similar to that used to hold wash lines (Photo 2). A close inspection revealed burned flesh on the end of the hook.
At this point I had determined where the electricity exited the technician's body, but I had yet to uncover where it originated. Further investigation revealed that at some point prior to the incident, the fluorescent tubes had been removed from a luminaire mounted on the outside of the north face of the building, but the luminaire was still fully wired.
I determined that the building had been built prior to the NEC requirement that a continuous grounding wire be carried through the conduit. Subsequent versions didn't permit conduit to be used as the ground path. I also noted that the thin wall conduit that supplied power from the circuit breaker load center to the luminaire had separated at some point in the past. This separation only severed the continuous ground path that existed throughout the circuit (i.e., the conduit). One end of the luminaire was attached to a section of conduit that fed back into the bank and, apparently, fed another luminaire or appliance. However, that conduit had been severed and the wires removed from it. In addition, the ballast in the outside-mounted luminaire had failed, causing the ungrounded conductor to fault to the frame of the luminaire, and thus energizing the housing of the luminaire and any sections of conduit attached to it.
I used a volt-ohmmeter to verify that the thin wall conduit connected to the luminaire was energized at 120V. And by checking continuity, I was able to verify that the thin wall conduit attached to the joist and mounted with the screw-in hook was grounded all the way back to the circuit breaker load center. After energizing the power to the bank, I verified that a 120V potential existed between the two pieces of conduit. This verified that the conduit that ran along the floor joist was at ground potential and the conduit attached to the luminaire and that entered the bank from the North elevation was energized at 120V.
Photo 3 shows the arc damage to the thin wall conduit coming into the bank from the lumninaire mounted on the North elevation of the bank (right arrow). Photo 3 also shows the arc damage to the thin wall conduit mounted parallel to and running alongside the floor joist. This is the conduit that leads back to the circuit breaker load center, which offers a continuous path to ground.
The verdict. Given the evidence at hand, I concluded that as the alarm technician inadvertently contacted the energized stub section of thin wall conduit connected to the luminaire, the conduit clamp penetrated the inside of his left thigh, creating a good conductive path from the energized thin wall through his left hand, down through his body, and out through the contact between the conduit clamp and the inside of his left thigh. The current caused his heart to fibrillate and stop beating.
By taking the luminaire on the North elevation of the bank out of service improperly, the person or organization that did so established conditions for a potentially catastrophic failure at some time in the future; said catastrophic failure would most probably be arcing of the faulted ballast, which would cause surrounding combustibles to ignite and possibly burn down the bank. By not removing the section of conduit that re-entered the bank from the outside luminaire, they also established conditions for a deadly electrocution.
In addition, the person or organization that installed the thin wall conduit failed to use a proper conduit clamp in the installation and the hook used to hold the conduit was a direct cause of the alarm technician's electrocution.
After my investigation was complete, the coroner found evidence on the victim's body that corresponded with and confirmed the results of my investigation. As a result, the alarm technician's estate filed a wrongful death case against the bank, which eventually went to trial.
The plaintiff's attorney asked me to testify to the fact that it was foreseeable and predictable that a catastrophic failure would occur due to the luminaire being taken out of service improperly. In response, the bank's attorney attempted to show the jury that the incident was so abnormal that there was no way anyone would be able to predict that an electrocution would have occurred.
I told the defense attorney that it was foreseeable and predictable that a catastrophic failure would occur as a result of the luminaire being taken out of service improperly. However, I made the distinction that I would only have expected the bank to burn down when the luminaire's ballast faulted, overheated, and ignited the surrounding combustibles. I would not have predicted that someone would be electrocuted.
The jury agreed with my findings that the catastrophic failure was foreseeable and predictable and they awarded the plaintiff approximately $1 million for the wrongful death.
Peserik is a forensic engineer, fire and accident investigator, and the president of James E. Peserik Associates, Inc. in Coopersburg, Pa.