Understanding Equipotential Grounding and EPZ Grounding Grates

For utility workers who are operating wire pulling equipment or temporary substation equipment, the threat of electric shock from unintended energization and induction voltage is all too real. Creating an equipotential zone (EPZ) of protection minimizes the risk of life-changing or life-ending incidents on power line projects.

OSHA requires that an equipotential zone be established at worksites where differences in electric potential are possible. Steel EPZ grounding grates that are engineered and tested are the ideal way to create an equipotential zone and protect crews on the ground.

What is an equipotential zone, how do these zones work, and how do EPZ grounding grates compare to other methods of creating an EPZ? This guide highlights the key points.

Equipotential zone definition

An equipotential zone of protection eliminates the possibility of a difference in electric potential between any two points, including any two points on a worker’s body, such as two feet or one hand and a foot. That difference is what puts workers at risk of electric shock or electrocution. When people, trucks and equipment are bonded to the same electric potential (“equi” means “equal”), the risk of current flow is reduced to near zero.

To understand the concept, think of a bird on a high-voltage power line. The bird is sitting pretty for one reason: Both of its feet have the same electric potential. As a result, no current travels through its body. If the bird were to stretch a wing and touch a second power line with a different electrical potential, electricity would flow through the bird’s body, killing it.

Why is an EPZ necessary?

Utility workers on the ground can be exposed to a difference in electric potential in a number of ways. For example, a wire being strung can accidentally become energized if it touches or comes near an energized wire due to an unforeseen circumstance such as equipment failure. Current always chases ground, so the current will travel to the wire pulling equipment on its way to the earth and shock workers who are touching it or standing near it.

At a temporary substation, if an electrical fault occurs, the current will enter the earth, creating a shock hazard for workers walking on the ground nearby or touching a fence or another object with a difference in voltage than the voltage on the ground.

How are EPZs created?

Electric utility workers and electrical contractors can use different methods of creating an EPZ, some of them more effective and reliable than others.

At the least-reliable end of the spectrum are metal chain link fences or hog wire panels placed on the ground. These makeshift solutions create a false sense of security. They are untested and may not get the job done when it counts, especially if they sink into the mud or are destroyed by trucks or heavy equipment such as bulldozers. In addition, they create a tripping hazard.

EPZ grounding mats made of wood or composite with wire mesh or a steel grate on top are a better option. However, they may warp, bend or break down over time from wear and tear, rot due to wet conditions, or snap under heavy machinery, creating an immediate safety risk. Some have not been rigorously tested to ensure they meet applicable electrical utility safety standards.

The most stable, durable and reliable solution is conductive galvanized steel EPZ grounding grates. These are positioned on the ground, then bonded together with 4/0 copper cables and two-hole lug connectors. A ball stud, which can be screwed into any of the open tabs on the grate system, is the point at which equipment is bonded to the EPZ.

When installing grounding grates, it’s smart to also install a transition pad made of fiberglass that makes it safe to step onto and off of the grates from the ground (earth).

Maximize safety and sustainability with steel EPZ grounding grates

Steel EPZ grounding grates offered by United Rentals are engineered for maximum safety. They have passed a host of KEMA performance tests, including electrical short circuit capacity tests and electromagnetic induced current withstand tests, each performed under multiple scenarios.

The engineered and tested grates not only increase safety but also help companies avoid project delays that could impact the budget. They provide stability and traction on soft or uneven terrain and won't shift under moving equipment or materials. They hold up well in harsh weather conditions, are reinforced for tracked vehicles and can withstand up to 100,000 pounds of pressure per square foot. Crews can connect and install them quickly, and additional grates can easily be added to extend the EPZ.

For companies looking to lighten their environmental impact, EPZ grounding grates offer several advantages. They are reusable and have longer lifespans than wood or composite EPZ mats. They help protect sensitive ground under trucks and heavy equipment and can be thoroughly cleaned to ensure that no contaminants or invasive species are transferred between sites.

Electrical lineworkers have one of the top 10 most dangerous civilian jobs according to the Bureau of Labor Statistics. Companies can keep crews on the ground safer—and remain compliant with OSHA standards—by putting adequate protections in place. Because current cannot flow without a difference in electrical potential, equipotential zones are critical. An EPZ created from steel EPZ grounding grates can make the difference between life and death for workers trying to do their jobs and return home safely at the end of each shift.

Request an EPZ grounding grate quote for your next electrical project.