A project I was managing in a 120-unit apartment complex involved the replacement of electric strip heat with hot-water baseboard. The old strip heat was removed, the wires were abandoned in the walls, and the circuit breakers were to be removed, disabling the old system. The boilers were installed in outbuildings serving 25 separate apartment buildings. A premanufactured polyethylene-insulated pipe assembly connected the boilers to the copper heating-hot-water circuits in each building.
One worker had been working on a baseboard cover when he grabbed a doorknob to help himself up and, at the same time, turned off a light. He shouted out in pain and surprise, having received a substantial electrical shock. He was pretty excited, but otherwise fine.
I used a multimeter to test the light switch and did not find a problem. I tested voltage between the door handle and a ground socket in an outlet and found 120 v. The door was made of metal and was on a metal frame. An aluminum cover we installed to hide the piping was in contact with the metal doorframe. All of these components were hot. In fact, the baseboard in the entire eight-unit building was hot. However, the worker was not shocked until he grounded himself on the metal cover of the light switch. We then turned off the breakers, which de-energized the piping.
What happened was that the old heater circuit had not yet been de-energized. The occupant had turned on the circuit breakers. Presumably, a baseboard mounting screw pierced the insulation of a heater wire, even though a thorough investigation of all of the exposed covers and piping had not revealed any contacts. The plastic piping completely isolated the copper from the ground, so a short to the baseboard or piping could energize the entire system, but would not trip a breaker because there was no current to ground.
Grounding was not included in the specifications. The mechanical engineer was not familiar with the electrical codes regarding grounding requirements, and the electrical specifications dealt only with de-energizing the old baseboard wiring and wiring the boiler rooms. (Even if there had been metal-pipe-to-ground contact, electrical codes have specific rules about grounding metal pipes.) A change order was issued to ground the pipes.
The minor shock to a worker led to the discovery of a very dangerous situation. If this had not happened, some future incident with a frayed light cord could have resulted in injury or death.
Conservation Services Group Syracuse, NY
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