Many a seasoned electrical worker will tell you that 120V is low voltage and pretty much harmless. More than one electrician has told me — with almost some form of professional pride — that they have been shocked many a time by 120V yet no harm has befallen them. There are even those few old timers who talk of how they commonly test “low-voltage” circuits to see if they are live by touching the leads with the back of their hand. After all, as they are quick to point out, 120V isn't dangerous — unless you get locked on. And even then, the risk is minimal. If you share this cavalier attitude, blatantly discounting the danger of 120V, the following case should make you think differently.
The accident. For one 45-year-old electrician, the day began like most work days. As an experienced electrician, he was tasked with making an electrical connection between an outdoor pedestal box and a 120V irrigation system controller. Considering that he'd performed this task many times before, he certainly felt no real foreseeable risk of injury.
The pedestal was the demarcation boundary between the legal domain of the electric utility and the property owner. The rear of the pedestal (electric utility side) was wired to a transformer. Two 120V phases and a neutral were connected from the transformer to the pedestal box. Mounted on a cement pad, the pedestal was fairly typical. There was ongoing construction so the pad and road were on a dry man-made earthen embankment spanning at least 5 feet above the surrounding unexcavated ground.
Two “car-stop” pipes, filled with cement and painted white and measuring 5 inches in diameter, were imbedded in the earth in front of the box to provide protection for the pedestal from traffic on the road. A ground wire was connected to the pedestal box and also connected to a ground rod that was driven into the earth a short distance from the cement pad. The back of the pedestal was locked with the appropriate electric utility tags. All in all, this appeared to be a pretty standard arrangement.
No meter had yet been installed in the pedestal. As such, the gap between the electric utility's domain and that of the property owner was not bridged — and the front of the box was not energized. To any experienced observer, this job truly appeared to hold minimal risk.
Upon beginning his work, the electrician touched one hand to the top of the pedestal box and the other to one of the “car-stop” poles. He immediately noticed a mild electrical buzzing sensation and then broke contact. Asking his assistant to bring him a “Wiggy” (electrical tester) to determine what might be energized, he proceeded to test between the pedestal and the pole, giving him a clear indication that something was energized. Believing that the pedestal, which was obviously connected to a ground post, was not the source, he assumed the pole was the culprit, chose not to touch it further, and went about his work.
While crouching down, he reached with his right hand to unlatch the front door on the pedestal while steadying himself with the other hand by grabbing the second “car-stop” pole, which he quite reasonably assumed would not be energized. Suddenly, he found himself locked into an electrical circuit. Unable to free himself from the latch on the pedestal or let go of the pole, the electrician fought to break free, using his legs to launch himself back into the middle of the road after 3 to 10 seconds of electrical exposure.
Although the electrician was able to get up and move about immediately following the incident, his assistant called for an ambulance and notified the electric utility. Soon after, however, the victim began to experience muscle fatigue and shooting pains going down his arms and neck. This progressed to tightness in his shoulders and chest pain. Over time, the symptoms grew to include fatigue, dizziness, tingling, generalized weakness, and that “pin-and-needles” feeling we've all felt on occasion. In the end, he was diagnosed with bilateral carpal tunnel syndrome as well as cervical degenerative disease. He also developed personality changes and experienced mood swings and anxiety.
The evidence. After more than 1 hour elapsed before representatives from the electric utility arrived, the immediate determination was that the neutral had been reversed with one of the phases in the electric utility side of the box, which energized the pedestal to 120V. Had there been a working ground, there would have been an immediate short circuit to ground when the equipment was initially energized, which would have drawn attention to the mis-wiring before any injury could occur. There was also no question that the ground had failed too — most likely because it was driven into dry, hard, and elevated earth.
There was clear negligence on the part of the company that installed the pedestal. The non-functioning ground coupled with the mis-wired phase was a potentially lethal error. (Note: The pedestal was installed by a company contracted by the electric utility and per the agreement, it was indemnified by the utility.) Litigation was initiated against the installer of the pedestal and the electric utility.
The investigation. I was contacted by the plaintiff's attorney and retained as an expert to reconstruct the incident and explain how such a significant electrical injury could occur from a mere 120V contact that lasted only a few seconds. My investigation consisted of a review of the medical records, all pertinent depositions, and a site visit. My goal was to reconstruct the electrical environment and relate the symptoms to the electric shock. I was deposed and later offered courtroom testimony.
Two major issues were challenged by the defense. First, it argued that the shock could not have occurred as the plaintiff testified, asserting that the plaintiff could not have gotten his hand locked behind the latch on the pedestal. Second, it maintained that the victim's symptoms were extreme — if not ridiculous — for a mere 120V contact.
My job was to educate the jury on the facts of low-voltage electrical injury. I made the group aware that a shock of 120V, especially when sweat is present, could have driven a current approaching or possibly even exceeding 500 milliamps into the plaintiff's body. After reviewing a video frame by frame (see photos above) in which the plaintiff demonstrated how he grabbed the latch, it was obvious that he could have easily gotten a finger or two into such a position that the current flow, which vastly exceeded the human let-go current (14 milliamps for adult males), would have locked him in place until he was able to break free. Under the circumstances, a 3- to 10-second shock was completely reasonable.
More important, I offered testimony about a little known primary response to electrical contact in which individuals can suffer a broad array of debilitating symptoms from even a brief contact with 120V, which I call diffuse electrical injury (see Table) For more information on this topic, see the article on page C10 of the June 2004 issue of EC&M, “What Happens When Electricity Doesn't Play by the Rules?” or visit www.ecmweb.com/mag/electric_happens_electricity_doesnt/index.html. Although not well known, it is well documented and raises the risk from any 120V contact to a very serious level.
Finally, I discussed secondary injuries, which are those that occur as the result of impacts and falls when one breaks free from an electrical contact. Although not propelled back by the electricity, the effort to break free can often lead to serious blunt force injury and painful activation of previously unexpressed diseases such as cervical degenerative disease. Although I could not state which of the plaintiff's symptoms were primary or secondary, it was certainly obvious from the chronology — coupled with the electrician's lack of prior medical history — that the plaintiff's injuries had a clear and absolute causal connection to the electrical injury that he suffered. Although the jury did find partial fault on the part of the plaintiff, it still returned a verdict of $3.3 million on his behalf.
The bottom line in this case is no amount of money will return the electrician back to health, nor will it make up for the loss of his career and business that took years to develop. Although liability clearly falls on the defendant for crossing wires and for not verifying that a ground placed in an elevated embankment was ineffective, this story would not have to be told if the electrician had recognized the risk from a 120V contact. Don't tell those who experience the full impact of contact with 120V systems that it's no big deal — 120V can debilitate or even kill.
Morse is a researcher and consultant, and serves as a full professor of electrical engineering at the University of San Diego.