Arc Flash Safety Eguide

CSE Arc Flash Safety eGuide Sponsor Overview Preventing Arc Flash Incidents By Design Integrating Electrical Safety With Design Protection, Arc Flash Mitigation Using Internal VFIs In Liquid Substation Transformers White Paper: Arc Flash Safety In 400V Data Centers Sponsored By Sponsor Overview Sponsor Overview Preventing Arc Flash Incidents By Design Integrating Electrical Safety With Design Protection, Arc Flash Mitigation Using Internal VFIs In Liquid Substation Transformers White Paper: Arc Flash Safety In 400V Data Centers At Eaton, we’re energized by the devices. Solutions for harsh and We power businesses with reliable, challenge of powering a world that hazardous environments. And engi- efficient and safe electrical solutions. demands more. With over 100 years neering services. Along with the personal service, experience in electrical power man- support and bold thinking to answer agement, we have the expertise to Eaton is an expert partner for helping tomorrow’s needs today. Follow the see beyond today. engineers specify electrical systems charge with us. that exceed the exacting standards of Whatever the challenge, Eaton deliv- commercial construction, data cent- Eaton.com/followthecharge ers with innovative solutions. Power ers and other projects. From ground- distribution and circuit protection. breaking products to commissioning Backup power protection. Control support, critical industries all over the and automation. Lighting and secu- world count on Eaton. Sponsored By rity. Structural solutions and wiring 2 Preventing Arc Flash Incidents By Design Understanding electrical buses in distribution equipment. The increase can knock personnel off distribution equipment and flash is immediate but the resultant their feet. Sponsor Overview its associated risks can help release of energy can cause severe reduce incident energy levels injury, and possibly death. There is Each year, more than 2,000 people Preventing Arc Flash and save lives. a potential for a tremendous amount are treated in burn centers for inju- of heat to be released, which can ries from arc flash incidents. Many Incidents By Design By Bruce W. Young, PE, Bala result in overpressures, as well as injuries caused by arc flash incidents Consulting Engineers Inc., King flying debris. The energy released can be prevented. Not working on Integrating Electrical of Prussia, PA. can cause temperatures exceed- or around energized equipment may ing 35,000° F, which can vaporize be the simplest way to avoid injury. Safety With Design Anyone involved with electrical steel, copper, and aluminum. Inhal- Scheduling maintenance outages distribution systems—either as a de- ing these vaporized metals could be may seem like a bother, but will Protection, Arc Flash sign engineer, commissioning agent, fatal. Injuries or fatalities could occur easily offset the loss of production, Mitigation Using Internal or contractor—for more than five if personnel are in the area in front unscheduled outages, and equip- years probably has been directly of an arc flash, which could send ment damage that may occur with an VFIs In Liquid Substation involved in an arc flash incident or projectiles such as parts of metal arc flash incident. Transformers has heard of one. buses away from the blast. Also, molten metal can cause significant Arc flash hazard analysis According to NFPA 70E: Standard burns, and the sudden air pressure Sometimes working on live electri- White Paper: for Electrical Safety in the Work- cal equipment may be necessary. Arc Flash Safety In place, arc flash is a “dangerous con- Appropriate PPE is required when 400V Data Centers dition associated with the release working on or around energized elec- of energy caused by an electrical trical equipment. An arc flash hazard arc.” It is measured in terms of arc analysis is required by NFPA 70E. flash incident energy, which is used This determines the arc flash bound- to determine the appropriate level ary, the incident energy at the work- of personal protective equipment ing distance, and the level of PPE (PPE), and in terms of an arc flash that must be used within the arc flash protection boundary. boundary. An arc flash is the result of an Procedures for performing an arc electric current passing through air flash hazard analysis can be found as the result of conductor failure, This arc flash label indicates that the breaker in IEEE 1584: Guide for Performing settings used in Figure 1 result in conditions equipment failure, or the accidental that require personnel to wear Category 3 Arc Flash Calculations. Some of the connection between voltage sources PPE within the flash boundary. factors that determine the amount of Sponsored By such as dropping a tool across Courtesy: Bala Consulting Engineers Inc. incident energy include: 3 • The available fault current at the at the line side circuit: This is the amount of current of the device Sponsor Overview that could flow into the circuit in the and another event of a fault. This is calculated on the load Preventing Arc Flash in the short-circuit analysis. Factors side of the de- that determine fault current are the vice. Energy Incidents By Design available fault current of the power levels at the source (typically available from the line side and Integrating Electrical local power utility), the impedance load side may of the transformers that supply the be significant- Safety With Design circuit, length and type of conductors ly different. in the circuit, and motor contribution. This differ- Protection, Arc Flash At first, it may seem counterintuitive, ential should Mitigation Using Internal but higher fault currents may actu- be identified ally reduce the flash hazard because to provide VFIs In Liquid Substation they will decrease the overcurrent maintenance Transformers device clearing time, which reduces personnel the flash hazard. with informa- White Paper: tion regarding • The operating characteristics of potential arc Arc Flash Safety In the overcurrent protective devices flash hazards. 400V Data Centers in the circuit: These vary with the Even with the type of device used. These charac- main breaker opened, the line side of the labels are installed, work on this teristics are determined by simple the main is still energized. equipment or routine maintenance fixed settings on thermal magnetic will likely be required at some point. breakers, fuse melting curves, and Equipment labeling Work that may be required could be multiple pickup settings on relays After the arc flash hazard analysis thermal scans to check for equip- and solid-state breakers. Settings for is completed, warning labels are ment hot spots, racking out a breaker adjustable devices are determined in printed and affixed to the electrical for routine maintenance, or installing a coordination study. equipment. The labels should include a new circuit breaker to serve new the level of PPE required, the flash loads. • Equipment labeling require- hazard boundary, the flash hazard, ments: For distribution equipment the shock hazard, and approach Regardless of the work to be done, that has a main overcurrent protec- distances. personnel must follow the appropri- tive device, two labels may be re- ate safety procedures. Observe the Sponsored By quired: one label for the energy level After the study is completed and label to determine the proper PPE 4 Sponsor Overview Preventing Arc Flash Incidents By Design Integrating Electrical Safety With Design Protection, Arc Flash This arc flash label indicates that the breaker settings used in Figure 2 result in conditions Mitigation Using Internal that reduce the boundary hazard and lower VFIs In Liquid Substation the PPE requirement to Category 0. Courtesy: Bala Consulting Engineers Inc. Transformers exists. Therefore, it is critical that personnel working on electrical distribu- White Paper: tion equipment be trained in proper Arc Flash Safety In procedures, and that they wear the 400V Data Centers appropriate PPE. Reducing incident energy levels at a location where electrical work is to be performed reduces the level of PPE required when working on energized Figure 1: This graph shows breaker settings and the corresponding time-current curve for circuits at that location. However, selective coordination requirements. Courtesy: Bala Consulting Engineers Inc. energy incident level reduction does not eliminate PPE requirements. level, gear up, and carefully proceed maintenance tasks, the temptation to perform the necessary work. PPE may be to proceed without proper Figure 1 shows a time-current curve may be as simple as safety glasses, PPE to save a few minutes. But even (TCC) for a 1,600 A, 480 V, solid- gloves, and untreated cotton—or it with the most careful work, accidents state trip-unit circuit breaker with could include a full face shield and can happen, and the potential for adjustable long time pick-up, long Sponsored By protective suit. For minor or simple serious, life-threatening injuries still time delay (LTD), short time pick-up 5 100% arcing fault level of 3,540 A will last approximately 13 sec. Using Sponsor Overview the maximum arcing exposure time of 2 sec as recommended in IEEE Preventing Arc Flash 1584 results in an arc flash hazard of 22 Cal/cm2 and requires Category Incidents By Design 3 PPE as indicated on the warning label (see inset). Energy levels above Integrating Electrical 1.2 Cal/cm2 can cause a temperature rise that will result in second-degree Safety With Design burns on exposed human skin. Protection, Arc Flash When energized maintenance is Mitigation Using Internal required for this equipment or down- stream equipment, the energy level VFIs In Liquid Substation and required PPE may be reduced Transformers by setting the LTD to 0.5, the STPU to 1.5, and the STD to instantaneous, with the resulting TCC shown in Fig- White Paper: ure 2 and its corresponding warning Arc Flash Safety In label shown in the inset. These set- 400V Data Centers tings reduce the arcing fault durations (the 85% and 100% fault levels) to 0.02 sec.

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