Why Prefer Source Impedance Data over Infinite Bus Calculation for Arc Flash Studies

Why Prefer Source Impedance Data over Infinite Bus Calculation for Arc Flash Studies

A utility company may be reluctant to provide the source impedance (fault data) on the primary side of the utility transformer for an Arc Flash Study for several reasons. Understandably requests for utility data might be delayed due to a reduction in staff and increased workloads. However from a liability standpoint some may assume that it is better to provide the utility customer with the maximum fault current believing that this will result in the highest arc flash PPE category, and that their risk of liability is greater if an arc flash injury occurs and the source input data is less than the maximum fault current value. Is this line of reason in the best interest of the utility company or its customer? Who is responsible to evaluate the worst cast incident energy results and what input data should be used?

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ARC FLASH….BOUNDARY, WHAT ARE THE LIMITS?

WHY AN ARC FLASH STUDY?

Recall that as part of the electrical safety program, per NFPA 70E ® -Article 110.7 The employer shall implement and document an overall safety program that directs the work activity appropriate for the voltages, energy level, and circuit conditions. If the work involves electrical hazards Article 130.3 states that a an Arc Flash Hazard Analysis shall determine the Arc Flash Protection Boundary and the personal protective equipment that people within the Arc Flash Protection Boundary shall use. As a result of the employer is responsible to promote electrical safety in the work place. As facility managers work to implement arc flash safety they want the answer to the following question:

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WHY AN ARC FLASH STUDY?

WHY AN ARC FLASH STUDY?

Commercial and industrial facilities depend on reliable electric power without interruption. This is especially the case for facilities with mission critical systems. Localized generators, UPS systems and other equipment is typically installed prevent a momentary loss of power to critical loads. Because the distribution equipment remains energized during routine maintenance, the workers can be exposed to both electric shock and Arc Flash Hazard. It is therefore essential to provide a work plan that identifies the arc flash hazard category level and Personal Protective Clothing and Equipment to reduce the risk of injury or death.

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