An arc flash occurs when an electric current passes through the air instead of along its intended path. The result is extremely high heat that can cause severe burns, blinding light, and an explosion that can result in hearing damage and potentially fatal injury. Multiple arc flash incidents occur every day in workplaces across the United States.

Safety of your employees and contractor employees should be always at the forefront. There’s urgency to completing arc flash risk assessments and shock risk assessments: According to changes made for NFPA 70E 2015, these as-assessments must be conducted before any person is exposed to electrical hazards. The risk of an arc flash explosion occurring at your facility is not negligible, and the trend of increased power use combined with aging electrical infrastructure across the U.S. heightens the danger. The Electrical Power Research Institute (EPRI) estimates direct and indirect costs to an employer from a fatal electrical accident in the millions of dollars.

Navigating all of the requirements, conditions, and exceptions that result from these assessments requires a great familiarity with the new standard. Specifically, NFPA 70E 2015 Section 130.4 requires that a shock risk assessment be performed before beginning energized work, and NFPA 70E 2015 Section 130.5 requires that an arc flash risk assessment be performed to:

  1. Determine whether an arc flash hazard
    exists
  2. If a hazard exists, determine:
    1. The appropriate safety-related work
      practices
    2. The arc flash boundary
    3. The correct PPE to be worn

Wells Engineering is a leading engineering firm in performing power system studies. Our Professional Engineers assure that the arc flash assessments they perform, and which our customers provide to their personnel, are backed up by solid engineering calculations and practices.
We would appreciate the opportunity to discuss the arc flash assessment requirements of your facility with you.


Steps for an Engineered Arc Flash Analysis

Step 1: Data Collection
Qualified staff must gather data from all applicable electrical equipment. Required information includes:

  • Data from the utility, including available fault current, operating voltage, and specifics regarding the utility’s protective equipment at the point of service.
  • Specifics for each protective device in the electrical system, including manufacturer, model, available time/current settings, and short-circuit interrupting rating.
  • Transformer impedance, tap settings, and ratings.
  • Conductor specifics, including lengths, sizes, and types of all overhead lines, bus ducts, and cables.

Step 2: Power System Modeling
One-line diagrams must be developed or updated to show the current configuration and modes of operation for the power system. Accurate electrical system drawings are necessary to identify power sources, voltage levels, electrical equipment and protective devices. If you already have one-line diagrams, we will update the data and work from them, if possible. Wells Engineering utilizes SKM Power Tools for Windows for system modeling & Analysis.

Step 3: Short Circuit Study
A short circuit study is required to determine the magnitude of current flowing throughout the power system at critical points at various time intervals after a “fault” occurs. These calculations will be used to determine the bolted fault current, which is essential for the calculation of incident energy and interrupting ratings of your equipment. Comparison of equipment ratings with calculated short circuit and operating conditions will identify underrated equipment. We perform this study in accordance with ANSI Std. C37 and IEEE Std. 141-1993 (Red Book).

Step 4: Protective Device Coordination
Protective device coordination should be performed to ensure selection and arrangement of protective devices limits the effects of an over-current situation to the smallest area. Results will be used to make recommendations for mitigation of arc flash hazards. Although this is an optional study, arc flash mitigation cannot be performed without completing this step. We perform this study in accordance with IEEE Std. 242- 2001 (Buff Book).

Step 5: Arc Flash Calculations
These calculations are based on available short circuit current, protective device clearing time and distance from the arc. Calculations of incident energy levels and flash protection boundaries will be completed for all relevant equipment busses. The magnitude of arc hazards are determined using methods from NFPA 70E, IEEE 1584 or NESC Tables 410-1 and 410-2, as applicable.

Step 6: Reporting
Upon completion of the calculations, we will prepare your Arc Flash Hazard Analysis Report. This will be supplied to you for a short review period, during which your team can review mitigation recommendations. At this point, we can hold a Management Summary meeting to interpret the report results. Upon approval, we will provide a final report and full sized one-line diagrams, stamped by our Registered P.E. The drawings and report will also be supplied to you in a digital format.

Step 7: Label Installation
We will generate and install arc flash hazard warning labels. These labels identify incident energy and working distance, nominal system voltage, and the arc flash boundary. In addition to standard requirements, our labels also include Limited, Restricted and Prohibited approach boundaries, date, upstream protective device and recommended personal protection equipment. We can also provide bolted fault current if desired. We provide labels that are compliant with NFPA 70E 130.3

 

Are you in need of an Arc Flash Analysis? Contact Wells Engineering today at 859-282-7538.

 

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