New restriction to methods of reducing arc energy

The Code: Section 240.87(B)

Method to Reduce Clearing Time

One of the following means shall be provided and shall be set to operate at less than the available arcing current

(1) Zone-selective interlocking

(2) Differential relaying

(3) Energy-reducing maintenance switching with local status indicator

(4) Energy reducing active arc flash mitigation system

(5) An instantaneous trip setting. Temporary adjustment of the instantaneous trip setting to achieve arc energy reduction shall not be permitted.

(6) An instantaneous override

(7) An approved equivalent means

Other Notes

  • Arc energy reduction is designed to limit the arc-flash energy that could be exposed to workers on the load side of an overcurrent device.
  • The incident energy in an arcing event is directly proportional to the time frame a fault will be permitted to persist.
  • The final setting of the instantaneous trip is what determines whether or not additional arc energy reduction techniques are required
    • This final setting is determined by the electrical system requirements such as inrush characteristics or selective coordination, not the minimum setting of the instantaneous trip
  • Arc energy reduction is not achieved with an instantaneous trip being adjusted to a lower setting while a worker is working on the equipment, and then adjusted back to the desired setting after work is complete