What features to look for in arc-flash relays
This white paper informs specifying engineers, original equipment manufacturers, designers, and end users about the most important features in arc-flash relay technology so that they can select the best relay for their application.
Arc-flash relays are vital to mitigating an arc flash. Every system is not the same, nor are arc-flash relays. To effectively protect against an arc flash, select a relay that is the best fit for the facility’s system.
The most important features of an arc-flash relay are
- Reaction time
- Trip reliability
- Ease of installation
- Sensor flexibility
- Software
- Sensor design
- Avoidance of nuisance tripping
- Scalability
Arc-Flash Mitigation Basics
Arc-flash relays can quickly detect a developing arc flash by sending a trip signal to the circuit breaker, which reduces the total clearing time and any subsequent damage. They do this by providing an output that directly activates an electrical system circuit breaker, which cuts off the current flow to the arcing fault.
Arc-flash relays help companies comply with the NEC, which, in certain cases, requires workers to adjust the circuit protection device to instantaneously trip when working inside an arc-flash boundary. The code says that workers do not need to take this extra step if an arc-flash relay is protecting the cabinet.
The installation of an arc-flash relay reduces the total clearing time and the amount of energy that is released through an arcing fault. The fastest arc-flash relays can detect a developing arc flash and send a trip signal to the breaker in less than 1 millisecond. The circuit breaker will open 35 to 50 milliseconds later. Because an arc flash can draw a fraction of bolted-fault current, especially in its initial stages, circuit breakers alone should not be relied upon to distinguish between the arcing current and a typical inrush current.
With an arc-flash relay, there is less damage to equipment, as well as fewer and less severe injuries to nearby personnel. This damage is usually minor and limited to the fault point where the arc originated. This avoids the more widespread and severe damage that occurs during a full-blown arc flash.
Arc-flash relays are an important part of an arc-flash mitigation strategy. Download the white paper for a deeper discussion about the features of arc-flash relays.
