Arc Flash Hazard Calculations Using IEEE 1584-2018

Introduction to the Changes in IEEE 1584-2018

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 to increased hazard 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.

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, and no longer includes 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.

Reduced Arc Current

The new guide retains methods to consider reduced arc currents and their ability to increase trip times.  The variation is revised from a fixed 15% reduction to one that varies based on voltage, with less reduction at higher voltage levels.  Previously limited to low voltage equipment, the new arc current variation correction factor is applied throughout the entire voltage range.

Arc Sustainability in Low Voltage Equipment

An explicit omission of equipment below 240 V fed by a transformer of 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.

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.  When applying a maximum time limit, new language advocates the use of engineering judgement and consideration of the work task to account for situations when a person’s egress may be blocked.

Other Notables

  • The model retains support of single-phase calculations with conservative results
  • Supported frequencies are explicitly 50 Hz or 60 Hz, and are no longer inclusive of those in between
  • Working distances less than 12 inches are now considered within the plasma cloud and are not supported
  • System grounding is no longer considered based on new test results showing no significant impact
  • Incident energy at the boundary distance is now defined as 1.2 cal/cm2
  • Special equations for current limiting fuses and circuit breakers are moved to the informative annexes

Webinar Video - IEEE 1584-2018 Update – An Introduction to the Changes

In this webinar, given by Jim Phillips, founder of BrainFiller.com, ArcFlashForum.com and also Vice-Chair of IEEE 1584 and International Chair of IEC TC78, Jim takes you through the long history of what it took to develop the next edition including establishing a collaboration between IEEE and NFPA, creating a project team for the almost 2000 new arc flash tests, model and equation development and more. He then discusses the major changes, why they were made and what they mean. The changes include equations for five different electrode configurations, more choices for enclosure sizes, an enclosure correction factor calculation to adjust for specific enclosure sizes, and the grounded vs. ungrounded difference has been eliminated.