Like any energy source, an electrical circuit is a ticking bomb, just waiting for the right conditions to blow. As Finley Ledbetter, CEO of Group CBS (Addison, TX, groupcbs.com), explains, “A twisted pole, faulty interlock, and enough energy will turn an electrical firecracker into mortal lightning strike.”
Protecting personnel from arc-flash and arc-blast dangers isn’t an option — it’s mandatory according to OSHA and NEC requirements. According to Ledbetter, compliance starts with an accurate arc-flash calculation based on real field tests that can pay double dividends when the findings are used in a preventive-maintenance (PM) program. “But realize,” he cautions, “any time electrical equipment with sufficient fault current is operated, there is a danger. And PPE will not always protect workers.”
Ledbetter offered several tips for managing arc-flash risks.
—Jane Alexander, Managing Editor
Avoid common mistakes.
Technicians refer to the National Electrical Code (NEC), Tables 130.7(C)(9-11), which define hazard risk categories (HRCs) for various classes of equipment, as well as what level of PPE employers need to provide to employees based on the minimum arc thermal performance value (ATPV). A common mistake is to determine the HRC and required PPE level based solely on the class of equipment instead of the actual 70E standard requirements. This approach assumes that the fuse or circuit breaker will actually perform to the OEM specification. A failed OCPD or even a slow breaker will result in higher incident energies than your technician’s PPE protection when the arc-flash calculation is based solely on OEM specifications.
Develop a maintenance-planning schedule.
Good maintenance is a first line of protection against arc flash/blasts. NFPA’s 70E Article 205.3 requires that all electrical equipment be maintained in association with the OEM instructions or industry standards. NETA’s maintenance frequency MTS table, based on equipment class and an environmental condition, is a good place to start when developing your PM-planning schedule. The best way to determine the arc-flash danger for a given device in a given installation is to use IEEE’s standard 1584 arc-flash calculations based on actual test data for the given device at a given installation.
Know that not all switchgear is arc-flash resistant.
Older switchgear and panel boards were not made with built-in remote actuators and extraction/racking capabilities, even though myth has it that switchgear is designed with arc-flash containment in mind. OEMs have started to develop switchgear cubicles with integrated remote actuation and racking/extraction features, and you can easily search the Internet for the latest equipment design. For a premium, this switchgear allows your technicians to actuate the OCPD or other device while it is still behind the metal enclosure. Arc-flash-resistant switchgear also strives to direct the arc flash up and away from the technician. Arc-flash-resistant switchgear that complies with IEEE C37.20.7 with remote actuation and racking/extraction is a move in the right direction, but it can be prohibitively expensive to replace all your aging switchgear with new enclosures and gear.
Use remote actuation and racking systems to keep your distance.
A number of portable remote actuation/extraction/racking systems work on virtually any OCPD or motor-control center and enclosure. Rather than having an embedded unit for each cubicle, these systems come with a portable design and power supply. In some cases, the technician can stand as far as 500 ft. away from the gear in question, well outside the arc-flash and arc-blast danger boundaries. These portable systems can also provide PM data on the force required to rack a unit. The best examples of remote racking/actuation work with horizontal or vertical racking systems, use magnetic latching that does not require any modification to existing equipment, and accommodate a variety of equipment makes and models. MT
Through a number of affiliated companies in the U.S. and U.K., Group CBS Inc., Addison, TX, provides electrical solutions and services for customers in the industrial, utility, power-distribution, and repair markets around the world. For more information, visit groupcbs.com.