Section 3: Appendices A: Arc Flash Technical Information
The Arc Flash Study was conducted to find out what personal protective equipment (PPE) is needed to work live on each piece of electrical distribution equipment (such as switchboards, panelboards, control panels, motor control centers, and other equipment). PPE is only needed if the owner chooses to work on the equipment live. When working on electrical equipment, there are three separate conditions that should be considered. The first and most ideal condition would be to create an electrically safe work environment. When working on electrical equipment, a way to accomplish this would be to de-energize the equipment and use lockout/tagout procedures. If the first condition is not obtainable, the second condition would be to minimize the exposure to the hazard. A hazard analysis must be completed to identify the hazards and how the worker might be exposed to them. An example would be to install electrical equipment that is designed for personnel to work energized, while eliminating their exposure to the energized equipment (an example of this would be using switchgear with draw- out breakers instead of switchboards). The third and least desirable condition would be to wear arc flash PPE. PPE is the last line of defense to guard against injury because it is the only barrier between the worker and the hazard. Refer to NFPA 70E-2021 130.1 for additional information. Interstates recommends striving for a safety program that relies on the first two conditions. The following assumptions were used to calculate the Arc Flash values: • Power distribution modeling software, was used for developing Arc Flash results. Calculations are based on IEEE 1584-2018. • Default arc length values, which are based on IEEE 1584-2018, are 32mm (~1.25 inches) for switchboards and 25mm (~1 inch) for MCCs, panelboards, and control panels. • Manufacturer’s circuit breaker values for fault durations were used in calculating the fault clearing time. • We are using the current industry standards to calculate the arc flash energy and approach distances based on the IEEE 1584-2018 calculation. • NFPA 70E 2021 was used to determine the limits of approach and the protective clothing characteristics. As stated in IEEE 1584-2018, equipment at or below 240V that is fed by a transformer and has less than 2kA available fault current does not create enough energy for an arc fault to be maintained. A default clothing protection of 1.2cal/cm 2 will be required as a minimum when working on this energized equipment. Equipment above 50V is required to be addressed by NFPA 70E-2021, however single-phase equipment is not accounted for in IEEE 1584-2018 as no conclusive research has been done to establish a consistent calculation method. It is recommended by Interstates that all single-phase equipment not evaluated in the arc flash study is addressed through standardized safety procedures utilizing proper shock protection equipment and 1.2 cal/cm 2 clothing.
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