Substation and Arc Flash Risk Assessment

Equipment Evaluation

An equipment evaluation compares the available short circuit current with the interrupt rating (IAC) of the device at that point in the distribution to determine whether the device is capable of safely interrupting current in a fault condition. Devices with insufficient interrupt rating will not properly interrupt current as they are designed, but instead will cause a catastrophic failure resulting in significant equipment damage and additional potential arcing event.

Panelboards, switchboards, motor control centers, and other electrical equipment must be able to withstand the available fault current. An equipment evaluation is performed:

  • To determine if the electrical equipment is rated to handle the available fault current present at that node in the system
  • To determine if components responsible for interrupting current have a sufficient interrupt rating
  • Identify what grade equipment to purchase for upgrades or equipment replacement.

NEC Article 110.9 states that “Equipment intended to interrupt current at fault levels shall have an interrupting rating at nominal circuit voltage sufficient for the current that is available at the line terminals of the equipment.”

Equipment Labeling

An important safety objective of an Arc Flash Risk Assessment is to inform workers of the risk of an arc flash potential by labeling electrical equipment. Labels identify life saving information. These requirements are specified in the 2014 NEC 110.16 code and state that “all switchboards, panel boards, industrial control panels, meter socket enclosures and motor control centers” be labeled. The NEC code has been amended in the 2014 update with clarification to include “switchgear”.  Warning Labels should be clearly visible to qualified persons before examination, adjustment, servicing, or maintenance of equipment and contain enough information for them to select procedures and PPE.

The labels are required to meet the NEC 2014 111.21(B) code which states that where caution, warning, or danger labels are required, they must meet three requirements (the use of effective words, colors or symbols).  According to NFPA 70E, 130.5(H) Arc Flash hazard equipment labels must contain the following:

  1. Nominal system voltage
  2. Arc Flash Boundary
  3. At least one of the following:
    • Available incident energy and the corresponding working distance, or the arc flash PPE category
    • Minimum arc rating of clothing
    • Site-specific level of PPE