Alan Drew, Author of The American Lineman, Retired SVP of Research and Development at NLC
Storm season is here. Hurricane Fiona caused an island-wide power outage along with heavy rainfall, fierce winds, and severe flooding to Puerto Rico and then weeks later, Hurricane Ian made landfall in Fort Myers, Florida and wreaked havoc across the state all the way over to Daytona Beach and Orlando. This time of year, and into the winter months ahead, extreme weather can create dangerous working conditions and environments for electrical lineworkers across the country. As we continue to move through the storm season, we want to share a helpful article on grounding and bounding during extreme weather.
This article will focus on regulations, procedures, and best practices that should be followed to safely work on de-energized lines during extreme weather conditions. The scenario is that a host power company experiences a catastrophic event that causes significant damage to its system. It assumes that damage to the T&D systems is severe with structures and conductors damaged that are both in the air and on the ground. Multiple crews or a single crew could be assigned to repair the damage and restore service. It is also assumed that crews could be any of the following:
- Host power company crews and personal
- Mutual aid power company crews from outside the area
- Line contractors
The scenario includes the possibility that multiple crews from any or all the crew types could be working together to repair damage and restore service.
With the increase in the use of portable generators and behind-the-meter solar generation and storage, precautions must be taken to prevent back-feed into the cleared line section. Several measures can be taken depending upon the interconnection at the meter.
- The solar disconnect switch can be opened, locked, and tagged
- The meter can be removed
- Or the service can be disconnected
Some power companies have ground sets that crews use on the secondary side of transformers. In any event, lineworkers must be aware of back-feed sources when clearing and working on lines. In addition, any sources of induced voltage shall be considered as a source and proper precautions taken.
Applying Personal Protective Grounds
Temporary protective grounds are to be placed at such locations and in such a manner as to prevent each employee from being exposed to hazardous differences in electrical potential. The proper size and type of grounding devices must be selected. Testing the circuits that have been cleared prior to grounding should be stressed in every way.
In the case of multiple crews working under one clearance, it is a common practice to install master or bracket grounds near the clearance points such as open jumpers, open switches, or open disconnects. These are intended to function as tripping grounds that will create a fault current to open the nearest protection device in the case of inadvertent energization. They should not be considered personal protective grounds for lineworkers working on the cleared section. Each crew will apply its own personal protective grounds at the worksite as appropriate.
In the case of a single crew working on their own clearance, they might provide tripping or bracket grounds at clearance points and then personal protective grounds at the worksite. They might also provide just personal protective grounds at the work site. When several spans of conductors are down it can be practical to install personal protective grounds at a point where the conductors leave the ground and rise to a pole that is still in the air.
Personal Protective Grounds Should Provide an Equipotential Zone
Insulating and isolating a lineworker is the only way to completely prevent current from flowing through that lineworker. This is the usual approach to performing live-line work. However, for working on de-energized lines and equipment, use protective grounds. Protective grounds act as a direct, low-resistance path to ground in order to:
- Minimize the time it takes to trip the circuit.
- Limit the current flow and voltage drop across the lineworker’s body.
Equipotential zone (EPZ) grounding provides a low-resistance, short-circuited connection from the line to a ground source. It creates a zone of protection to reduce hazardous differences in electrical potential between objects in the work area. EPZ is the best grounding method for limiting current flow through the body and should be applied to the structure being worked on.
Bracket grounding provides a low-resistance, short-circuited connection from the line to a ground source at key locations on one or both sides of the work site.
The bracket grounding method has been used for decades to help protect lineworkers. But over time, research proved that EPZ grounding provided better protection for the lineworker. As EPZ grounding became more common, the role of bracket grounding evolved. It is now used primarily to trip the line’s protection devices as quickly as possible. This protects the worker and the system as a whole.
If the line becomes accidentally energized with only bracket grounds installed, hazardous levels of current will flow through the lineworker’s body. Even with an EPZ in place, small amounts of current will flow through the lineworker because the EPZ grounds and the lineworker form a parallel path to ground.
EPZ and bracket grounding work together to accomplish the two purposes of grounding and bonding.
Key Considerations
- Some power companies and line contractors have adopted the practice of marking grounds during a widespread clearance with multiple crews involved. This consists of installing an orange or green flag (app. 24 inches x 24 inches) on the grounds at the top of the pole. This makes it easier to observe the grounds when they need to be checked or removed. The grounds can also be tagged, listing the crew member in charge and contact information.
- Workers on the ground may be exposed to step and touch potentials even if personal protective grounds have been installed adjacent to the work area. To provide adequate protection when crews are working between grounds on the ground handling conductors, many companies are requiring the use of rubber gloves and super dielectric overshoes.
- When line conductors must be cut into or spliced back together – the use of a grounding jumper as a bypass should be considered. In some cases, a grounding mat may be a good choice to minimize potential differences.
We hope these tips can help you and your company be efficient and safe during this storm season. We’re grateful for all those involved in helping to aid those in need during such extreme weather events like hurricanes or ice storms. Together, we can help make the industry and world a safer place.
For more information, please see OSHA 1910.269
