Facility and Utility Systems - Analysis/Design/Construction

Arc Flash

Arc Flash

Please contact us with any questions related to arc flash studies, NFPA 70E, electrical system documentation, or protective device coordination. We would be happy to discuss your current situation as it relates to these issues and work with you to design an electrical safety program so that your facility can be as reliable as possible, while keeping your employees safe.

What is an arc flash?

Arc Flash is an intense release of energy due to an arcing fault between phases or phase to ground in an electrical system. The cause of the fault normally burns away during the initial flash and the arc fault is then sustained by the establishment of a highly-conductive plasma that can reach 35,000 degrees F. This energy release creates light, heat, shrapnel, and pressure waves which can cause severe burns, hearing damage, and even death.  Some common causes of arc flash events are tools shorting phase conductors, breaks or gaps in insulation, dust and other impurities on the surface conductors, and equipment failure.

Why does my facility require an arc flash study?

Compliance with the Occupational Safety and Health Administration (OSHA) involves adherence to a six-point plan:

  • A facility must provide, and be able to demonstrate, a safety program with defined responsibilities.
  • Calculations for the degree of arc flash hazard.
  • Correct personal protective equipment (PPE) for workers.
  • Training for workers on the hazards of arc flash.
  • Appropriate tools for safe working.
  • Warning labels on equipment. Note that the labels are provided by the equipment owners, not the manufacturers.

The National Fire Protection Association’s (NFPA) 70E standard outlines the components of a complete electrical safety program. NFPA 70E is not required by law but the Department of Labor has clarified that following NFPA 70E arc flash guidelines meets OSHA arc flash protection requirements.

What does my facility gain from an arc flash study?

  • Compliance with OSHA requirements for a safe workplace.
  • New or updated electrical system drawings for your facility.
  • An arc flash study report with detailed information of your facilities electrical system.
  • Arc flash labels for electrical equipment guiding employees and contractors to the proper PPE selection for performing work.
  • Recommendations for making your electrical system safer.

How is an arc flash study performed?

The first step is to collect system and installation data.  A field comparison of the existing single line diagrams against existing conditions is made and the single line diagrams are updated and made current. This is an obligation of the engineer performing the study.  Further, it is an obligation of the system owner to maintain and keep this data up to date.  To do this the engineer or assigned contractor must visit all equipment to be analyzed to collect nameplate data, circuit breaker data and trip settings, physically verify fuse types and ratings, and physically verify feeder sizes.

In order to properly assess the fault current and arc flash hazards the engineer must determine the system’s normal and any secondary modes of operation. This addresses alternate utility feeds, backup generators, etc.  The worst-case scenario is always used for generating hazard data.

Once the data is collected and the modes of operation are known it is time tocreate a software model of the electrical system. This entails inputting all of the data collected to make the single line diagram up to date.  All wire sizes and lengths, fuses, circuit breakers, etc. are modeled.

The completed model then has calculations run to determine fault current at every key point in the electrical system in a number of fault scenarios.  This key information is used to ensure that all equipment is properly rated for that available fault current.

The next step is to evaluate the protective device coordination. This is to ensure that in the case of a fault, the correct device will trip to minimize fault time. A well-coordinated system will have the nearest upstream device trip quickly. If problems are found, changes are recommended to reduce arc flash hazard values.

With the fault current known and the coordination evaluated there is enough information to run arc flash calculations. This has a number of steps:

  1. Determine the amount of Incident Energy generated during an arc event (calories/cm2).
  2. Determine the Approach Boundaries for qualified and nonqualified personal. This is determined by the Incident Energy value as well as the enclosure type.
  3. Determine the types PPE required based upon the Incident Energy calculated.

With the arc flash evaluation complete and verified by the engineer it is now time to generate and apply labels.  The labels proposed have all of this data recorded on them. It provides trained personnel with all of the data necessary to work safely.

Along with the labels the engineer generates a report with all of the results (fault current, coordination, arc flash calculations) and brief explanations as well as recommendations to make the system safer if any problems are encountered.