Plumber Electrocuted

[노영진]

Plumber Electrocuted After Installing Unsafe Temporary Power Connection at New Construction Residential Housing Development

Mar 1, 2009 12:00 PM, By Chris Shiver, P.E., Cerny & Ivey Engineers, Inc.

Plumber is electrocuted at residential housing site after rigging improper temporary power connection

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When plumbers Jim and Dave arrived at a new residential development, their task at hand certainly seemed routine — performing trim-out work (installation of fixtures and appliances) in a partially completed house. Once on-site, however, they quickly hit a snag.

After realizing that the mostly finalized electrical system in the house was not connected to the electric utility, they questioned the general contractor (GC) on the availability of power for their tools. The GC promptly directed them to a temporary construction pole setup on the adjacent lot.

Photo 1. Face of subject GFCI receptacle after removal.

Not considered an out-of-the-ordinary request on a new construction residential project, this situation did not raise any red flags for the plumbers; however, the events that soon unfolded would quickly turn this typical job into tragedy.

Setting the stage

As he approached the temporary power location, Jim found that an unconnected length of Type NM cable was lying loose on the ground between the temporary pole and meter base of the house they were working at, with the house end routed into (but not connected to) the meter base.

He recalled that a few days earlier he had seen an electrician using this NM cable to create a temporary service connection for the house — to enable testing of the wiring and fixtures. Apparently, the electrician had left it in that location, he thought to himself, possibly for follow-up testing/troubleshooting use. Based on this assumption, Jim recreated the connection (as he thought the electrician had done) and succeeded in energizing the house wiring, enabling the use of lighting and tools. Next, Jim and Dave began working on different levels in the house, with Dave in the basement installing a water heater.

The accident

Both plumbers worked separately for some time, with Jim occasionally coming down to the basement to check on the water heater installation. During at least one of those visits, Dave mentioned to Jim that he'd received a few electrical shocks while touching pipes or other bare metal. Because they'd experienced similar occurrences at other locations in the past without any ill effects, neither man was overly concerned.

Soon thereafter, Jim went outside to speak to another plumber (Mike), and then returned to the basement, only to find Dave sitting on the floor — slumped back against a furnace installed adjacent to the water heater. Assuming Dave was pulling a prank, Jim immediately scolded him. However, when Dave did not respond, Jim shook him and received an electric shock. Jim immediately ran outside to get help from Mike. The pair quickly called 911, moved Dave away from the metal-cased appliances, and administered CPR until emergency medical services arrived.

While watching the medical responders work on Dave in the basement, Mike touched the furnace casing, received a shock, and yelled for someone to shut off the power to the house to prevent further injury. Another contractor (Roger), who had responded to the incident, ran outside and disconnected the NM cable from the temporary power pole. Prior to making that disconnection, Roger noted the connection details at the temporary pole and also observed the connection details to the meter base on the house where the accident occurred (click here to see Figure). His account of those details proved crucial to determining fault in this case.

Unfortunately delayed by the lack of street names and map information for this new housing development, once on the scene medical responders were unable to revive Dave. As suspected, medical and forensic examination later indicated that Dave had died from electrocution with the fatal current probably passing from one arm to the other through his chest.

Investigation and analysis

Because a fatality was involved, OSHA performed an inspection at the work site within a week of the accident. This investigation was followed by inspections of the involved electrical systems and hardware at the site by several engineers, including myself. I became involved in the case as the technical representative of the insurance carrier for a major electrical equipment manufacturer, which had provided some of the temporary electrical setup hardware.

Prior to the OSHA visit, the NM cable, which was originally lying loose on the ground before Jim reconnected it, reportedly was fully removed from its connection points at both ends (temporary pole and house). Therefore, Roger was the only person known to have a recollection of the connection details at the time of the accident (plumber Jim was unsure). As detailed in the Figure, Roger's recollection indicated that the NM cable was probably a 10/2 + ground configuration. The connections reportedly did include insertion of the two insulated conductor's previously stripped ends into the slots of a GFCI-type receptacle at the temporary pole, as diagrammed. However, they did not include the bare conductor in the cable. His description also indicated connection of the previously stripped opposite insulated conductor ends to one of the meter base hot leg lugs with the other conductor end connected to the neutral. (Note the polarity of these connections indicated in the diagram.)

Examination of the temporary power pole revealed it included four 120VAC GFCI-type duplex receptacles downstream of two 20A circuit breakers (two receptacles supplied from each circuit breaker). The components were mounted in an outdoor-type box with a damaged cover that would not properly close. The GFCI receptacle identified as the unit supplying temporary power through the NM cable was then removed for detailed laboratory examination (Photo 1). During this removal, proper supply connections within the temporary power pole assembly for that receptacle were confirmed, including bonding connection. It was verified that the neutral and ground were bonded together within the main service panelboard in the house — and that there was a bonding connection to the copper piping within the house from the panelboard grounding electrode connection point.

The diagrammed temporary terminations for the NM cable would have the effect of connecting the GFCI receptacle outlet hot leg with the service entry neutral in the house where the plumbers were working. This would have resulted in energization of any exposed bonded metal, including the furnace and water heater casings and metal piping, at voltage levels potentially up to 120VAC.

Photos 2a, 2b, and 2c. Subject GFCI internal conditions during laboratory examination.

The GFCI receptacle was confirmed as a UL-listed 20A rated indoor-only-type assembly with front-mounted “test” and “reset” buttons. The receptacle exterior evidenced some age and weathering, including heavy corrosion of the screw heads that secured the plastic casing. Investigators also confirmed that when connected to a nominal 120VAC supply, the outlets were live — a condition that did not change when the GFCI test button was pushed. During disassembly, the receptacle internals evidenced significant contamination from dirt, insect remains/webs, and other debris. External corrosion from probable water intrusion also was apparent. The unit evidenced heavy overheating/burn damage to the circuit board (Photos 2a, 2b, and 2c). Provided information indicated this GFCI receptacle was probably at least five years old. Based on these findings, it's unlikely that the GFCI circuitry would have reacted to the expected ground leakage currents and shut off power, following connection of the outlet hot leg to the house grounded conductors as described above.

Regulations and codes

After its investigation, OSHA cited the plumbing company for “serious” violation of four federal health and safety regulations:

1. Failure to instruct each employee in the recognition and avoidance of unsafe conditions and hazards, as required by 29 CFR 1926.21(b)(2).

2. Failure to ensure that electrical equipment is free from recognized hazards likely to cause death or serious physical harm to employees, as required by 29 CFR 1926.403(b)(1).

3. The path to ground from circuits, equipment, or enclosures was not permanent and continuous, as required by 29 CFR 1926.404(f)(6).

4. A ground conductor was attached to a terminal or lead so as to reverse designated polarity in violation of 29 CFR 1926.404(a)(2).

Particularly noted was no evidence that any of the plumbing company employees had been provided with safety instructions regarding safe usage or connection to temporary construction site power sources, proper testing and usage of GFCI-protected circuits, or typical construction site electrical shock hazards.

At the time of this accident, the 1996 National Electrical Code (NFPA 70/NEC) was in effect at the accident location. Therefore, the references below come from that edition. Article 305 addressed Temporary Wiring, with 305-2(a) requiring that all permanent wiring provisions apply except where specifically modified in this Article, and 305-2(b) requiring approval for any temporary methods. Additionally, 305-4(a) requires installation of services in conformance with Art. 230, and Sec. 305-5 requires that all grounding conform to Art. 250. Section 305-6 requires ground fault protection for all personnel utilizing temporary wiring installations.

The NM cable feed used as a temporary service for the house where the accident occurred clearly did not meet numerous Art. 230 requirements, including ampacity/size (230-23), clearances (230-24), and attachment (230-26). Section 250-23(a) requires that a premises wiring system connected to a grounded service should have a connection between the grounded service conductor and the grounding electrode conductor. This was not provided by the temporary connection completed by the plumbers, as noted in the diagram. The connection made to the temporary pole receptacle did not use an attachment plug, as specified in Sec. 410-56(f). Furthermore, the degraded temporary pole receptacle enclosure no longer provided the wet location protection required by Sec. 410-57(b).

Also in effect at the time of this tragedy was the 1998 edition of NFPA 70B, “Recommended Practice for Electrical Equipment Maintenance.” Chapter 12 of that edition emphasized the importance of maintaining GFCI devices in an operable condition for personnel protection. Specified was testing of these devices using the integral test means within the intervals specified by the original manufacturer. It was also noted that this testing should be documented on a permanent label or card installed with each device. The original manufacturer's installation and maintenance instructions for the GFCI receptacle involved in this incident were obtained. Specifying that the unit should be tested monthly, the instruction sheet included a removable card intended for installation with the GFCI unit to permit recording of monthly tests for up to 11 years. It also clearly indicated that the unit should not be exposed to rain, and must be contained in a weatherproof enclosure when installed outdoors.

Lessons learned

Because time is money for the developer and contractors on any job site, a “get-it-done” mentality tends to prevail. As was probably the case in this situation, a contractor's employees in need of a particular resource (such as temporary power) frequently attempt to obtain it by the most expedient means possible.

Unless training is provided on how to safely obtain those resources, as well as hazardous conditions to avoid, then unsafe actions are bound to happen. Such training must also provide clear incentives for acting safely and employment consequences for unsafe activities. Very telling to the inspecting engineers on this specific case were the reports that both men thought nothing of receiving electrical shocks while on this job site. Furthermore, if an employer criticizes an employee for the extra time consumed at a site in finding a safe temporary power source, rather than commending him for avoiding the more easily obtained but potentially unsafe power source, then all of the training in the world will be for naught. Ultimately, in this case and every other case, employers should have arranged for safe and easily accessed temporary power to be available at each work site where they assigned their plumbers. The OSHA citations noted above emphasized to the subject employer these planning and training deficiencies.

Use of the NM cable by a licensed electrician in the manner described several days prior to the accident, even for temporary test energization of the subject house, is at best questionable from a safety standpoint. It's also in clear violation of the NEC, as noted above. Further compounding this unsafe condition was the electrician's decision to leave the NM cable in a location that allowed and even encouraged other contractors to repeat this unsafe connection method. Unfortunately, the apparently limited understanding of electrical wiring connections by the plumbers resulted in the energization of the grounded portions of the electrical system and other bonded exposed metal within the house. That's one more reason why electricians should be trained to have an awareness of the potential consequences of their actions and decisions on other trades/persons who may enter a work site while they are present or at a later time.

The GFCI receptacle involved in this incident was a listed product that had been improperly exposed to weather over a long time period. The receptacle was installed in a temporary power pole that was one of reportedly many belonging to the electrical contractor for this project — and which supposedly had been reused at many locations. Apparent in this case was a lack of preventive maintenance or testing by that contractor, who should have identified the failed weather protection and the degraded receptacle condition and nonfunctional protection long before the time of this accident. Electrical contractors should have programs in place for tracking, inspecting, testing, and maintaining such equipment — for the protection of their own employees as well as others. This will also help to avoid financial consequences such as those resulting from the litigation following this tragic accident.

In the end, a sealed settlement was reached in this case prior to reaching court.

A registered professional engineer in eight southeastern states, Shiver is the executive vice president — principal engineer with Cerny & Ivey Engineers, Inc., Norcross, Ga. He can be reached at cbs@cernyandivey.com.