What Does Ground Hook Mean?
A ground hook is a conductive device used to ensure that a piece of previously energized equipment does not hold any additional electrical energy that could potentially harm workers.
When used, a ground hook is attached to a conductive device at one end and to the ground (or a suitable grounded object) at the other. This will cause any remaining energy held by the conductor to be discharged into the ground, rendering the device safe to work on.
The ground hook is also known by many other names, including ground cluster, temporary protective ground, and even just ground.
Safeopedia Explains Ground Hook
The use of a ground hook is a necessary safety precaution when working on previously energized equipment that could pose a danger if it became reenergized. While electrical equipment is supposed to be deenergized as part of standard lockout/tagout procedures, there are numerous ways for electrical equipment to become reenergized, such as static charge buildup, induced voltages and capacitive discharges.
Ground hook use is primarily associated with work around high-voltage systems; however, if there is the potential for the system to carry a large amount of electrical current, work on a lower-voltage system may also require the use of a ground hook. In the United States, the criteria for the use of personal protective grounding is covered by OSHA 1910.269(n) and NFPA 70E Section 120.3.
A key use case for ground hooks is to safely redirect energy to ground in the case of an electrical fault. The National Fire Protection Association (NFPA) specifically requires that any ground hook used on electrical equipment be able to conduct the maximum amount of fault current that could flow from a given electrical system, and moreover, specifies that it must be able to do so for a long enough duration that any nearby workers can clear the fault.
The ability of a ground hook to effectively dissipate the energy of a given system depends on its physical qualities. ASTM standard F-855 describes the specifications that a ground hook’s cable must meet in order to be able to adequately discharge a given amount of energy. It is dangerous to use a ground hook that cannot handle the amount of energy present in a system, as the excess current could cause the cable to vaporize, resulting in a potentially lethal arc flash.