The need to operate electrical equipment safely, without impacting facility operation, has been a priority for electrical engineers and maintenance personnel for many decades. Initially, much of the focus was directed toward shock prevention. In recent years, as NFPA 70E and NEC have evolved, significant effort has been invested in designing and producing equipment which mitigates the risk associated with arc flash.
Operating aging equipment, however, does not have to pose safety challenges. NFPA 70E addresses aging equipment, or equipment design features in several sections. The intent is to address aging switchgear through the application of good engineering and maintenance practices.
As the NFPA 70E technical committee finalizes the 2018 standard, let’s highlight some of the NFPA 70E and NEC sections that impact aging electrical equipment:
NFPA 70E Section 130.5(3) Consideration of Design and Maintenance
When conducting an arc flash risk assessment, the design of the overcurrent protective device and its opening time, including condition of maintenance, must be taken into consideration. Fault clearing time is the majority contributor in high incident energy locations. Aging infrastructure with electromechanical style protective devices can pose risk as these devices reach the end of useful life and begin to degrade operationally. Robust, active, maintenance planning combined with an effective equipment upgrade/modernization program can reduce this risk, often as effectively as new equipment.
NFPA 70E Section 130.2(A) (15) Energized Work
Energized work under NFPA 70E is allowed under four (4) basic exceptions: additional hazard or risk, infeasibility, less than 50V and normal operation. Although normal operation is not defined it is generally regarded as opening and closing a circuit breaker, switch, contactor or starter. Additionally, certain conditions must be met before normal operation of energized equipment is allowed. Those conditions are: properly installed, properly maintained, equipment doors are closed and secured, equipment covers are in place and secured, and there is no evidence of impending failure.
Aging equipment may fail to meet the conditions required to allow energized operation of its breakers, switches, starters of contactors, which constrains the ability to operate the equipment and poses risks to operators. Modernizing aging equipment can provide significant improvement to existing switchgear and afford the opportunity to mitigate risks associated with normal operations.
NEC Section 240.87 Arc Energy Reduction
As-is aging installed equipment is not required to meet the current code. However, the current code would be enforced when extending the life of existing equipment or replacing existing equipment to continue facility operations.
As mentioned earlier, time is the biggest factor in high arcing incident energy locations. NEC 240.87 requires a method of reducing arcing energy for breakers that are rated, or can be adjusted, to a continuous trip setting of 1200A or higher. The NEC also outlines several technologies that can be implemented into existing aging electrical equipment to mitigate arc flash and improve operator safety. These include zone selective interlocking (ZSI), differential relaying, energy reducing maintenance switch, active arc flash mitigation, instantaneous trip or instantaneous override set below the arcing current or an equivalent means.