After the arc flash hazard has been calculated, measures can be taken to reduce it. A risk analysis can identify the most urgent locations to qualify for action. The following solutions empower arc flash prevention:
- Changing Work Methods
The first solution to look for is to avoid the risk entirely. De-energizing equipment before working on or near it is the safest way to work. In situations where hazard levels are so high that mitigation is not even possible, it may even be the only option. - Reducing Arc Flash Incident Energy
The arc flash hazard depends mostly on three factors: distance, available fault current, and clearing time. Distance can sometimes be increased by changing work methods, which has a pronounced effect on hazard levels. Racking in and switching circuit breakers remotely can even reduce the hazard to zero. Some activities will remain where this is not an option. Reducing available fault current is rarely an option, as it is decided at the design stage. This leaves the clearing time to be lowered for the reduction of incident energy. A careful review of settings can result in a faster response from protective devices, but system coordination has to be considered. - Maintenance Switches
Reducing clearing time for arcing currents is an effective way to reduce incident energy, but it may negatively affect protective device coordination. Installing maintenance switches can overcome this downside by only temporarily reducing the clearing time of the device protecting the work area. Any modern digital relay can be modified to allow a maintenance switch to be installed, and retrofit kits are available for low-voltage circuit breakers. - Advanced Arc Flash Prevention
Special arc flash detection systems are available that combine light sensors with electrical current sensors. These sensors will trip very quickly for an arc flash detected inside switchgear or a room, but not on regular (downstream) faults. This detection can optionally be combined with a short-circuit and earthing device that turns an arc flash into a bolted short-circuit fault, removing most of the energy in the arc.
