Calculating Arc Flash Incident Energy Using IEEE 1584-2018

Introduction to the Chages in IEEE 1584-2018 (Draft 6)

IEEE 1584 Guide for Performing Arc Flash Hazard Calculations is a widely adopted and industry accepted standard that includes procedures to calculate and predict arc flash hazard levels. The guide is recognized by federal agencies, such as OSHA, and consensus standards, such as NFPA 70E, as a method to estimate arc flash boundary and incident energy when performing an arc flash risk assessment.

IEEE 1584 has remained mostly unchanged since its original publication in 2002, with two minor amendments in 2004 and 2011. However, subsequent IEEE papers shed light on parameters not previously considered that could lead increased hazards levels beyond those predicted by the original standard. Consequently, a collaboration between IEEE and NFPA was formed to advance research around arc flash events and the variables that affect their severity.

After analyzing more than 1800 tests, the IEEE 1584 working group constructed a new arc flash model. The empirically derived formulas in the new model are significantly more accurate, though equally more complex than those in its predecessor. The topics below address notable changes that should be considered when performing, administering, or complying with an arc flash risk assessment.

Note: The following observations are based on the latest publicly available (Draft 6) version of the new IEEE 1584. Though not recommended for use in advance of publication, the impact of expected changes can be assessed.

Voltage

The supported range of voltage in the new arc flash model remains unchanged at 208 V through 15 kV. Calculations for enclosed equipment greater than 2.4 kV are now based on test results, rather than extrapolation methods previously used. Low Voltage is reclassified as 208 V though 600 V, no longer including equipment up to 1000 V.

Bolted Fault Current

The range of bolted fault current supported by the new arc flash model is now dependent on voltage:

  • 208 V – 600 V : 500 A to 106 kA
  • 601 V – 15 kV : 200 A to 65 kA

Electrode Configuration

The previous version of the arc flash model was based on vertical electrodes in open air or an enclosed box.
Differentiation is now given to the following electrode configurations:

  • VCB: Vertical electrodes inside an enclosure
  • VCBB: Vertical electrodes terminated in an insulating barrier inside an enclosure
  • HCB: Horizontal electrodes inside an enclosure
  • VOA: Vertical electrodes in open air
  • HOA: Horizontal electrodes in open air

Enclosure Size

Consideration of enclosure size is refined in the new standard. Previously, a distance factor based on equipment type and voltage was used to account for the effect of enclosure size. The new standard applies a correction factor based on system voltage, electrode configuration, enclosure height, enclosure width and enclosure depth.

Electrode Gap

The range of electrode gap supported by the new arc flash model is now dependent on voltage:

  • 208 V – 600 V : 0.25 in. to 3 in.
  • 601 V – 15 kV : 0.75 in. to 10 in.

Acceptable Calculation Methods for Systems Out of Range

Acceptance of the theoretically derived Lee method for voltages over 15 kV or gaps outside of the range of
model was eliminated. The new standard recognizes that system parameters can fall outside the range,
however provides no specific recommendation of an alternative calculation method.

Consideration of Arc Current Variation

The new guide retains a method to consider variations of arcing currents and their ability to increase trip times.
However, the correction factor is revised from a fixed 85% to one that varies based on voltage. Previously
limited to low voltage equipment, this correction factor is now applied throughout the entire voltage range.

Arc Sustainability in Low Voltage Equipment

An explicit omission of equipment below 240 V fed by a transformer less than 125 kVA was cited by the previous
standard. Revised language indicates that sustainability may be less likely at 240 V or less when the bolted fault
current is less than 2000 A.

Reasonable Assumption of Maximum Arc Time (2 Seconds)

The new standard retains a recommendation to consider the likelihood a person will remain in the location of
an arc flash when arc time is longer than 2 seconds. However, new language advocates the use of engineering
judgement and consideration of work task when applying a maximum time limit.

Other Notables

  • Single-phase and DC systems remain unsupported
  • Supported frequencies are explicitly 50 Hz or 60 Hz, and no longer inclusive of those between
  • Working distances less than 12 inches are now unsupported by the model
  • System grounding is no longer considered
  • Arc flash boundary is calculated based on bare skin and no longer includes an adjustable factor for PPE
  • Special equations for current limiting fuses and circuit breakers are moved to the informative annexes