Numbers from the Bureau of Labor Statistics put electrical line work among the top ten most dangerous jobs in the United States.
One area within the electric utility and utility construction industry where we continue to see fatal accidents and injury involves line workers exposed to induced voltages on deenergized and grounded lines and equipment.
We have all seen the bumper stickers and signs on our substation fences that read, “if it’s not grounded it’s not dead”. While this is true, it does not really give us the whole story. It is more than that, it must be grounded and bonded in such a way it ensures that the circuit opens in the fastest available clearing time, and that the potential differences between conductive objects in the employee's work area are as low as possible.
Since 1994, OSHA has required grounding practices that will protect employees. OSHA’s intent is clear, temporary grounds and bonds shall be installed at the worksite in such a manner that keeps the worksite at the same potential and prevents harm to workers even if the line is accidentally re-energized or exposed to induced voltages.
To achieve as low a voltage as possible across any two conductive objects in the work area, we must bond all conductive objects in the work area. This very important work practice somehow is still being overlooked.
Recently, a utility contractor Crew Foreman was fatally injured while preparing to remove a jumper from a sectionalizing disconnect switch on a 115kV line. The plan of the day was to relocate two 115kV sectionalizing disconnect switches. There were two crews on the job working independent from one another.
Crew 1 established an equipotential zone (EPZ) between the switch structure, the sectionalizing switch, the wood pole down ground, the driven ground rod, and the 115kV transmission line. Crew 2 at established no EPZ because they did not bond the driven ground rod to the switch thereby establishing two different ground potentials between the switch stand and the switch. The Crew Foreman climbed up to the top of the switch stand to attach lift slings suspended from the crane. Once the lift slings were placed and pulled up snug, he positioned himself to assist in the removal of the blade end-sectionalizing jumper on B-phase. The crew foreman made contact with a difference of potential across the blade end of the insulator. The accident board concluded that the root cause of the fatal accident was the crew’s failure to establish an equipotential zone (EPZ).
In my 40 years in the industry, I personally have investigated several similar accidents where workers had been working on deenergized “grounded” lines. One thing I have found in common with these accidents was that the crews involved had been trained multiple times, as OSHA requires on equipotential grounding methods.
The dangers of induction are often underestimated; induction can kill. With more lines being forced into corridors and operated at higher currents, induction sources must be considered and respected.
EPZ grounding is a reasonable and technically sound provision for protective grounding of lines and equipment and it is fundamental to the safety of line workers. I find it remarkable that this well recognized concept of creating an equipotential work zone is not better accepted and established.
The purpose of the equipotential work zone is to minimize electric current flow across the worker's body. It is very simple and should be easily understood.Grounds installed only on either side of the work location or bracketed grounds do not prevent potentially lethal current from reaching and flowing through the worker. There is a belief with grounding that somehow those bracketed grounds are going to stop the electric current from reaching and flowing through the worker and it simply does not happen, the current takes every path.
Current regulations, if followed, will protected the worker from hazardous voltages. If an employee understands and follows grounding rules, they will be safe. As an industry, should we not have grown to the point that fatalities and injuries because of incorrect grounding practices is no longer the case?
Careful planning of work assures that the work is performed efficiently and safely and a hazard analysis is a critical part of work planning. A properly conducted pre-job briefing ensures the scope of work is understood, appropriate materials are available, all hazards including potential for induced voltage have been identified and protective measures have been established, and all affected employees understand what is expected of them. Knowing a hazard of induced voltage may be present and not determining how to properly protect workers from it is not enough. You must address how the hazard is to be neutralized and ensure everyone understands.
Think electrically, not mechanically
I believe that too many of our line workers do not fully understand the hazards of induction in their work. They see set of grounds in the area and believe that they are protected, they are thinking mechanically and not electrically. By this, I mean that they must be trained to consider themselves a component in an electrical circuit. All conductive objects in the work area that can be reached by the workers must be electrically bonded to eliminate differences in potential that the worker may be exposed to. Remember, “Think electrically, not mechanically”.