Equipotential Zones: The Importance of Choosing an Engineered EPZ Solution

Most utility companies do an excellent job of using equipotential bonding to protect lineworkers who are working aloft. Historically, they've been less diligent about implementing up-to-date equipotential zone (EPZ) procedures to protect personnel on the ground. If equipment at ground level unexpectedly becomes energized, employees including lineworkers and substation electricians may experience electric shock or electrocution. Such incidents are uncommon, but they happen, and when they do, they are often deadly.

Today, engineered and tested products exist that allow utilities and electrical contractors to easily create a reliable equipotential zone of protection. EPZs protect ground crews from hazardous energy by eliminating differences in electric potential between any two points on a worker’s body, known as step and touch potential. Without a difference of potential, current cannot flow.

Despite the availability of these products, many companies are still using improvised methods to create a ground-level EPZ, such as laying chain link fences or hog panel wire on the ground. These methods can create a false sense of security. They may not perform as hoped and can be easily compromised by trucks and equipment. They create tripping and electrical hazards for ground personnel.

IEEE, OSHA and most company safety committees are championing safer ground-level bonding and grounding work practices. These practices should be widely accepted by company leadership. Utilities that use outside contractors can require those contractors to set up an engineered and tested EPZ, much as they now require them to arrive on-site with the proper PPE.

Real-Life Shock Hazards that Put Workers At Risk
During conductor stringing or mobile substation operation, crews on the ground are vulnerable to step and touch potentials, transient voltages, induction and inadvertent energization. Any number of circumstances can cause hazardous potential voltage differences.

For example, when upgrading existing transmission conductor, there is a real possibility of equipment failure, which can cause loss of control of the conductor. Equipment failure can include puller-tensioner problems, connection failure between new and existing conductor and running block issues. Loss of control can result in the new conductor making contact with energized conductor or components, sending fault current back to a worksite.  Other potentially deadly hazards can include unforeseen vegetation issues and lightning strikes.

Induction hazards are among the most dangerous when working on or around electrical transmission class voltages. During conductor stringing, induction can occur when de-energized, grounded conductor runs parallel to energized conductor for long stretches. This scenario creates a circuit that can support electromagnetic induction, which can be realized at the worksite.    

Temporary substation workers may also be subject to step and touch potentials due to transient voltages, induction and inadvertent energization. While permanent substations have pre-installed ground grids, a temporary mobile substation is often located outside the footprint of an existing substation and typically requires a temporary EPZ. EPZ grates can be used to extend the substation ground grid outside the fence.

Benefits of Galvanized Steel EPZ Grates
Galvanized steel grates offer distinct advantages over other EPZ grounding mats, including mats that are made of wood or composite and topped with wire mesh or a steel grate.

 First and foremost, they are engineered to withstand up to 100,000 lbs of pressure per square foot and will easily support large conductor stringing and substation equipment. The grates have also been subjected to rigorous electrical testing by a reputable materials testing company.  They are more durable than mats made of wood or composite and won’t warp or deteriorate. Unlike EPZ mats that snap together, the grates float independently of each other and are connected only by 4/0 copper cables that create the electrical bonding.  As a result, they perform better on uneven ground.

 Galvanized steel grates are also faster to set up than most EPZ grounding mats. The grates can be set with a material-handling device including a lull or skid steer that has forks at least 6 feet long. Alternatively, they can be picked up via their lifting eyes with a utility boom truck or excavator.

 Ball studs supplied with each EPZ grate can be installed in any open receptacle, which allows equipment bonds and grounds to the EPZ to be kept as short as possible. This increases safety by reducing any whipping action that occurs if the bonds or grounds become energized.

Complacency Has No Place
It’s all too easy for utilities and electrical contractors to become complacent when they’ve been working incident-free for years or decades, but utility lineworkers have one of the most dangerous jobs in America. And of course, electrocutions happen when they aren’t expected.

 Making the investment in a reliable EPZ using steel grounding grates helps ensure that crews get home safe at the end of the day and return for their next shift to continue the important work of maintaining, repairing and upgrading the country’s electric power grid.

John McClendon is a regional product development manager at United Rentals, specializing in ground protection matting for the power distribution and transmission industry. With a deep understanding of product strategy and site-access solutions, he helps businesses enhance operational efficiency and minimize environmental impact. John is passionate about delivering innovative, customer-focused solutions that drive success in demanding work environments.