Arc flash relays are an effective defense against dangerous arc flash events, and the decision to include such a relay in a design is an easy one. Selecting the right relay for your application can be challenging. According to OSHA, industrial arc flash events cause approximately 80 percent of electrically-related accidents and fatalities among qualified electrical workers. Even if personnel injuries are avoided, arc flash can destroy equipment, resulting in costly replacement and downtime. In response, many designers are adding arc flash relays to electrical systems. These devices greatly mitigate the effects of an arc flash by detecting a developing incident and sending a trip signal to a breaker to disconnect the current that feeds it. Arc flash relays are complex devices, and an understanding of the technical details of their operation and features is essential. This white paper from our partners at Littelfuse covers key points of arc flash relay technology so that specifying engineers, OEM designers, and end-users can make an informed selection decision.
Arc Flash Mitigation
NFPA 70E goes into great detail on procedures to avoid electrical shock and arc flash events by opening and locking out circuit breakers before working on electrical equipment. When work on a live system is required, this standard spells out approach distances, use of personal protection equipment and apparel, and other precautions. Arc flash relays are an important part of an arc flash mitigation strategy and are often installed in electrical cabinets. These compact devices are designed to detect a developing arc flash extremely quickly and send a trip signal to a circuit breaker, which significantly reduces the total clearing time and subsequent damage. This is accomplished by providing an output that directly activates an electrical system circuit breaker to cut off current flow to the arcing fault. Arc flash relays can help companies comply with the NEC code, which in some cases requires workers to adjust the circuit protection device to zero-delay mode when working inside an arc flash boundary. The code states that workers don’t need to take this extra step if an arc flash relay is protecting the cabinet. The fastest arc flash relays available on the market today will detect a developing arc flash and send a trip signal to a breaker in less than 1 ms. The breaker will typically take an additional 35–50 ms to open, depending on the type of breaker and how well it is maintained. Because an arc flash can draw a fraction of bolted-fault current, especially in the early stages, circuit breakers alone cannot be relied upon to distinguish between the arcing current and a typical inrush current. That’s why installing an arc-flash relay to detect those developing incidents rapidly reduces the total clearing time and the amount of energy released through an arcing fault greatly. In turn, there is less damage to equipment, as well as fewer and less severe injuries to nearby personnel. Generally, this minor damage is limited to the fault point where the arc originates, and avoids the more widespread and severe damage that occurs in a full-blown arc flash. Learn seven key considerations when selecting an arc flash relay in this whitepaper from our partners at Littelfuse.
