When is the risk of arc flash highest for drawout circuit breakers?

The highest risk of arc flash for drawout circuit breakers occurs when racking the circuit breaker in or out. This process involves moving the circuit breaker into or out of the cell, which can create conditions favorable for an arc flash. When the breaker is being racked, there is a potential for improper contact or alignment, which can result in electrical arcing if the breaker is energized or if the equipment is not properly isolated before the operation.

During the racking process, the operator may be in close proximity to the energized components. If there are issues such as improper grounding or a fault condition, this can significantly increase the chance of an arc flash incident occurring. Proper procedures and safety precautions need to be followed to mitigate this risk.

While opening and closing the circuit breaker can also pose risks of arc flash, the actual act of racking it in or out places the personnel in a position where they are more vulnerable to the potential energy released in an arc flash scenario.