According to the National Fire Protection Association (NFPA), an arc flash hazard is “a dangerous condition associated with the release of energy caused by an electric arc.” An arc flash is an explosion causing severe burns, injuries and/or death depending on the severity. Arc flash incidents typically occur in applications above 120V and can take place when an electrical service is being inspected or serviced. In fact, some incidents occur when a worker is removing a cover or trim from a piece of equipment.
An arc flash can be caused by a reduction of the insulation or isolation distance between energized components such as when a tool is inserted or dropped into a breaker or service area, or when another conducting element is accidentally left behind that can compromise the distance between energized components. Often, incidents occur when an operator mistakenly fails to insure that the equipment has been properly de-energized.
Electrical switchgear equipment (sometimes just called switchgear or a switchboard) house circuit breakers that protect loads that can consume hundreds or thousands of amps of current. The procedure for making or breaking the electrical connections inside the switchgear between the circuit breaker and connectors in the switchgear is referred to as racking. Racking such circuit breakers is a procedure potentially wrought with personal danger to the operator's safety. A possibility always exists that an explosion will occur due to an arc flash, causing significant injury, including burns, or even death to the operator. One way to carry out a racking operation involves mounting the circuit breaker to rails in the switchgear, and sliding the circuit breaker into and out of a cradle of the switchgear. A hand or motorized crank (also called a racking tool) is typically used to urge primary connectors of the circuit breaker to corresponding connectors in the switchgear, which are electrically coupled to the line supply.
To perform the racking operation, the operator inserts the racking tool into a corresponding drive shaft that is accessible from outside the door of the compartment of the switchgear. However, it can be possible for this racking operation to be performed when the door is open. The door is designed to help withstand the explosive effects of an internal arc fault hazard, but when the door is open, the operator is fully exposed to the hazard. A racking operation should not be permitted when the door of the switchgear compartment is open to prevent this dangerous operation.