Arcing faults are not selective
Numerous arc flash burn injuries and deaths are caused each year by arc-flash explosions. Arc flashes present numerous dangers to electrical workers due to the extremely intense high-level heat generated in an arc flash and the pressure wave from an arc blast incident.
The electrical industry is continuously working to advance the level of knowledge and understanding of arc flash burn incidents. The development of NFPA 70E has provided a national work practice standard to deal with this hazard. This, along with OSHA law, is an effort to decrease the number of arc flash burn injuries that occur as a result of an electrical incident. Some recent advances have caused forward movement in safety and increased knowledge and understanding in this area.
The majority of this work and effort surrounds dealing with work on or near live electrical equipment. Placing electrical equipment in a "safe working condition" highly reduces or even eliminates the likelihood that an arc flash burn incident will or can occur and is required by federal law.
Arcing faults are not selective. They can injure or kill anyone within their vicinity, not just the person working on the equipment. Oftentimes this includes electrical inspectors. Equipment must be de-energized for inspection (if the doors are open or the covers are off).
If it is more dangerous to turn it off, wear adequate PPE for the distance from exposed, energized parts. Safe work practices are the key to the reduction in electrically related arc flash burn injuries; however, safe work practices work only when they are implemented. Implementing the practices and procedures available today will enhance worker safety and is critical to reduce the number of electrically related accidents that occur.
The above is excerpted from an article written by Todd Lottmann, electrical engineer, Cooper Bussmann, Inc. Todd is an alternate member of NEC Code-Making Panel 12 representing NEMA, a member of the UL 508A standards technical panel, member of NEMA 1IS Industrial Controls section, and involved with the NFPA 79 technical committee. Todd is the Bussmann IAEI representative participating in the national section meetings and various chapter meetings around the country.
Source: the Electricity Forum