Reducing Arc Flash Risks

Install Remote Circuit Breakers or Fuses to Improve Main Breaker and Bus Arc Flash Levels 

In many cases, arc flash levels at main switchgear, service entrance panels and their associated main breakers will be quite high because fault clearing depends on the operation of a primary fuse or relay. In many installations, the incident energy at the main switchboard may exceed 40 cal/cm2. In these situations, owners may determine it is not safe to allow any operation of circuit breakers or switches in the main equipment while it is energized. To mitigate this situation, a separate circuit breaker or fused switch can be installed upstream of the main switchboard. This device protects anyone working on the main equipment but is remote so that it can be included in the arc time determination since there is minimal risk of arc propagation in this situation. Of course, the incident energy at this new remote device will also be very high, but this approach would provide a lower energy level at the main switchboard and allow operation of the breakers and switches in the main board. 

Remote Operation and Racking 

Placing distance between electrical conductors and the worker greatly reduces the arc incident energy and the arc blast force. The reduction is not linear. For example, a worker twice as far as another worker from the arc will receive 25 to 50% less energy than the closer worker. New high voltage equipment can be ordered with the breaker “Open” and “Close” switches remote from the breaker unit. These could be placed on a non-breaker unit, in a separate control panel, or in a remote room. Older switchgear can be retrofitted with remote control switches. 

New microprocessor relays can be programmed to manually supervise the closing of a breaker using a “punch and run” time, which allows the operator 3 to 10 seconds after initiating a “close” to evacuate the vicinity before the breaker is actually closed. 

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