A few years ago at a company I worked for, an experienced, highly trained professional lineman, thinking he was lifting a truck ground, inadvertently lifted the ground rod connection for a transmission circuit bracket ground. Induction current instantly killed him as though he had made contact with an energized phase. The genesis of the incident was largely a lack of attention to details as everyone seemed to be aware of the risks and understood the purpose and need for the grounding that was installed.
In the past six years, I have personally consulted for 11 different companies that experienced fatalities associated with equipment grounding errors, and I am aware of several other similar incidents. A few months ago I was told of an incident where boom contact with a phase resulted in electrical injury to an employee, and workers on the scene thought that lack of grounding of the equipment had nothing to do with the electrical risk. In fact, it had everything to do with the risk. As an industry, we often are grounding to follow policy. Grounding mobile equipment is not sufficient to prevent injury. When we ground trucks to satisfy a policy, we frequently are creating death traps, not safe work sites. Understanding the electrical principles, proper planning, process, and integrity of grounding circuits and vehicles is just as critical to safety as any other connection we make on any distribution or transmission circuit. Until we understand that, we will continue to risk the lives of our workers in the field.
The Evolution of the Equipment Grounding Rule
The industry has wrestled for years with equipment grounding as a means to safety. In the remainder of this article, we will use the word “equipment” to mean any truck or mobile equipment that may become energized as a result of electrical contact. The 1994 preamble to OSHA 29 CFR 1910.269 observed that even though the phenomenon of step and touch risks around equipment was defined by Harrington and Martin in 1954 (AIEE Transactions, August 1954), the industry, including consensus standards and OSHA, still promoted grounding equipment as a means of protection for workers on the ground. In reality, OSHA and the standards did understand the limitations of grounding, but still maintained that grounding equipment was of great safety value. The issue was that the industry, where lineworkers were at risk, was largely uninformed about or unaware of the true risk and what to do about it. OSHA created rules recognizing the risks and limitations of grounding, but statistics and experience seem to indicate the industry hasn't quite gotten there yet.
Rule 1910.269(p)(4)(iii)(C) requires that every employee be protected from hazards that might arise from equipment contact with energized lines. In addition, (p)(4)(iii)(C)(3) requires grounding mats and (p)(4)(iii)(C)(4) requires barricades. Rules (C)(3) and (C)(4) are the two rules most often unobserved, yet they are quite possibly the most important when it comes to risk and protection of employees.
The reality is that the purpose of grounding is to cause immediate operation of a circuit protective device, not to protect workers from electrical contact. A worker in contact with grounded equipment energized by contact with an energized line or carrying current as a result of induction will be at risk from lethal touch or step potential unless the worker is at equal potential with the energized equipment and isolated from current flow. That is the reason OSHA mandates equipotential mats.
The Practical Application
The OSHA rule does not require that equipment be grounded, but it does have conditional criteria that may require grounding of equipment. A careful reading of 1910.269(p)(4)(iii) provides criteria for operating equipment near energized lines. If the equipment could become energized, there are mandatory requirements beginning with insulation or isolation. If those methods do not provide protection for every exposed employee, rule (p)(4)(iii)(C) mandates that equipment must be grounded, bonded together, equipotentially matted and barricaded.
The practical part is this: For all intents and purposes, no one can guarantee protection of workers on the ground if equipment becomes energized. This includes equipment set up under an energized line that could inadvertently fall on equipment. Since there is no possible guarantee of protection for those employees on the ground, even if the equipment is grounded, you are required by law to ground, bond, mat and barricade the equipment. Because the rule is written as it is, even the use of insulated overshoes – a popular method required by many employers – does not provide exemption from the mat and barricade rule.
Since we are discussing practical approaches, let’s briefly discuss the question about insulating blankets or insulated footwear. Insulated overshoes are voltage limited and cannot be tested to ensure electrical integrity, nor do they provide protection from workers who kneel down. However, if an employer could reasonably guarantee that insulated systems protect a worker from step and touch potentials from an energized vehicle, they might be eligible for a de minimis violation. As usual, Incident Prevention is not suggesting that you violate the direct rule. We are simply predicting questions from utilities that presently use overshoes as protection from step and/or step and touch potential around an energized vehicle.
Induction Risks are Included
When grounding plans are being developed for a work site, planners must recognize that induction risks must be treated just as energized contact risks. Grounding does not eliminate all electrocution risks from induced current. Where induction is present, grounding of the phases to a structure will electrically couple induction current through the grounds, through the structure and to earth. If equipment is connected to that same ground/earth electrode, induction current will flow to the equipment, creating electrocution risk. A worker who comes in contact with that equipment is exposed to lethal touch potential when they become the path for current flow from the equipment to earth.
The same risks exist at the tower. As an example, using a Delta Computer Systems SNT-02 Step and Touch monitoring kit, crew members and I measured 640 volts of earth potential at the base of a tower used to ground de-energized phases. The current measured was 40 amps on one leg of the tower. The practical protection from that risk is equipotential mats.
Utilities should have programs that address grounding for the protection of employees, and those programs must have training for employees so they understand the risks. As a key component, the program needs to deliver a thorough understanding of how current flows in grounded systems, the sources of current in grounded systems, the purpose of grounding and the lethal limitations of grounding for the protection of workers. Regarding the limits of protection provided by grounding, workers also must understand the methods of protection from those risks, such as the use of mats and barricades, as well as be provided the resources necessary to protect them from those risks.
As always, feel free to contact us about this article or any issue regarding industry safety. We'll be glad to direct you toward the many excellent resources available through Incident Prevention.
KNOWLEDGE, INSIGHT & STRATEGY FOR UTILITY SAFETY & OPS PROFESSIONALS
Incident Prevention is produced by Utility Business Media, Inc.
© 2004 - 2020 Incident Prevention™. All Rights Reserved.