electrical workers routinely racked out breakers in the normal course of their jobs LEVER RELAY They did this with little concern or knowledge of the hazards to which they were exposed. While all of us are more educated and knowledgeable today, many electrical workers still prefer the expediency of putting on a 40-cal suit over taking advantage of other available solutions LEVER RELAY
Today, there are state-of-the-art remote racking and switching systems that allow a qualified electrical worker to interact with circuit breakers from a distance outside of the arc flash boundary. This is a big step in reducing safety risks related to arc flash. Remote racking systems require a significant investment and take time to learn. This can lead to them being under-utilized in cultures that fail to understand the consequences of an arc flash and the available strategies to mitigate arc flash severity and exposure.
Three factors affect arc flash incident energy level:
Energy. The available fault current at a particular system location.
Time. How long it takes to clear a fault.
Distance. Proximity to the fault is exponentially proportional to its intensity.
These are the only levers available to reduce an arc flash event’s potential injury to electrical workers.
Energy
The first lever of reducing available fault current — energy — is the least useful. Facilities are commonly increasing the sizing (ampacity) of their power system equipment. Low-voltage switchboards of 4,000A to 5,000A are becoming increasingly more commonplace. This level of power is necessary for processes/manufacturing and to save cost over installing multiple smaller systems.
Outside the facility, the utility power system is designed to feed numerous systems (i.e., facilities). This translates simply into the idea that there’s plenty of fault current available, and there’s just not much that can be done about that (particularly at the service entrance). Arc-resistant switchgear is an attempt to mitigate these high-energy hazards. If you aren’t familiar with arc-resistant switchgear, picture military-tank-like switchgear with plenums (ducts) to route the force of a blast out of the room, thereby mitigating the likelihood of a switchgear explosion injuring a qualified worker.
Time
The second lever is the time or duration that an overcurrent fault can persist before system protection isolates the overcurrent fault. Traditional power system protective devices are coordinated to obtain a balance between power system reliability and equipment safety (not qualified worker safety). This reliability factor allows overcurrent faults to occur and persist for a second(s) while the downstream breakers closest to the fault time out and trip. Please note that each system has its unique coordination settings that determine the time delay during a fault.
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