When a Southern California plastics extruding company planned upgrades to its main switchgear distribution, an experienced and well-qualified electrical contractor was called upon to perform the work. As usual, he followed proper protocol. The plant would be shut down, and the contractor would set up temporary bypass power, allowing for the bussing in the gear and feeders to be increased for future capacity.
The local power company was notified — its equipment would remain energized to the back end of the main switch only. The main power switch was to be turned off, racked out, and locked out — all of which was done. The process proceeded as planned, and all necessary precautions had been taken, at least so it seemed.
The accident As the work progressed, larger feeders were being attached to the bus bars, and an apprentice was entangled within the gear to route and connect the wires. Tools were thrown about, and a torque wrench was laid across two phases of the bussing. Without warning, all of a sudden everyone heard the whine of the self-charging closing mechanism ramp up, followed by the distinct slamming sound of the switch being closed.
Once the switch closed, all 4,000A of power surged through the entire gear system, causing the torque wrench to become a conductor phase to phase and wire ends from the connections to the switch bus to energize. Pandemonium broke out as everyone scattered to avoid contact with the live wires and bus bars. Unfortunately, during this chaos, the apprentice became enmeshed in the live gear.
Hearing the victim's cry for help, one brave electrician ran to the main, managing to trip it back to “open” and disconnect the source power. Despite this brave effort, the apprentice's clothing was already engulfed in flames, and he was entangled in the shorted bus bars, which were covered with molten metal.
The crew immediately doused the apprentice with fire extinguishers and water, and the paramedics responded within four minutes of the 911 call, rushing him to the nearest hospital. Not surprisingly, considering the extent of his exposure, the apprentice had second and third degree burns all over his body and required long-term burn ward care.
The investigation I was called into the case much later by the plaintiff (victim) as a forensic expert to determine how the accident had occurred. The biggest unknown was unquestionably how had the main switch been reinstalled while still locked out with a long-shaft-type padlock. Although it was many years old, here was a major electrical manufacturer's equipment that had served the building quite well over the years with no documented problems. So how could the switch close all by itself?
After some investigation, all testimony of witnesses led to the same conclusion. No one was near the switch at the time of the accident; nor had anyone touched the switch after it had been opened and locked out. Therefore, there was no logical explanation for it to close — so it appeared.
Digging a bit deeper, I inspected the switch more closely. First, I had it impounded and sent to an off-site storage facility. Next, I contacted all of the other experts involved in the case to visually inspect the switch as well as examine its operation. The switch had a window that clearly stated “open” or “closed,” indicated by red and green backgrounds. As it is opened, the switch automatically recharged the spring-loaded closing mechanism, which assisted in reclosing of the switch when needed.
We opened and closed the switch again and again, each time locking it open with padlocks and lockout assemblies. Each time, no problems. Then something completely unexpected happened. By complete chance, when the switch was in the “open” position with a padlock on the lockout (as it had been at the time of the accident), someone accidentally bumped the switch from the side as we were moving it to another area in the warehouse to obtain better lighting. Lo and behold, the switch went “whir,” we heard a “bang,” and it was closed. We all were immediately astonished.
Upon closer examination, we determined that there was a small metal bar that kept the switch in the “open” position” that held back the recharging spring mechanism. Under the right conditions, this bar can be moved ever so slightly, allowing the closing recharging system to work and close the switch.
Immediately notifying the manufacturer and obtaining all possible data on this type of switch, we determined that this had actually occurred a few times in the past, as the manufacturer had redesigned the switch and recalled all known owners of the equipment for an upgrade. Unfortunately, undoubtedly due to owners of the building changing hands several times, this particular switch never received an upgrade.
The lesson The moral of this story is simple. Despite locks and indicators, the safest method is always to remove any source of power that can injure or kill your staff. In this case, the switch should have been cradled and removed from the entire gear. There should have been ground chains installed from each bus phase to ground to allow for an immediate fault in case of accidental energizing of the bus. Insulating gloves and blankets should have also been used on all bus bars not being worked on. My best advice is if you treat all electrical equipment as if it is “hot,” tragedies such as this can be avoided or diminished.
Nicholas, a forensic electrical expert, is president of JNLV Consulting Co., Las Vegas.