Arc Flash Calculations

This article was originally published in Current Connections Winter 2019 issue.

IEEE 1584 is the go-to standard used to calculate arc flash levels for just about every arc flash study done in the world. IEEE developed the original version of the standard in 2002 and based it on more than 300 arc flash tests. The new edition is based on almost 2000 additional tests. These tests proved that the original calculations have significant shortcomings.

Electrode Orientation
The 2002 edition was based on arc flash tests with electrodes (i.e., equipment busbars or MCC bucket stabs) only in a vertical orientation as shown in Figure 1.

The additional tests have shown that arc flash energy can be influenced by the electrode orientation, such as horizontal (Figures 3 or 5). These additional configurations may be possible with some types of electrical equipment – especially Figure 3 in MCC buckets or Switchgear cubicles. The new calculations will include five different configurations, as shown in Figures 1 – 5.¹

Now What?
The arc flash energy levels in the horizontal orientation are often 150% to 300% higher than the vertical orientation and 150% to 200% higher than the 2002 calculations. For equipment that has a Figure 3 orientation (MCC buckets, circuit breakers in switchgear), your current arc flash label is incorrect, and the incident energy levels are higher than shown.

For those of you responsible for the electrical safety of workers and contractors, consider the following actions:

  1. Update your arc flash study.
    a. This needs to be done every 5 years, per NFPA 70E, and now with these changes it’s especially important. Interstates, along with software vendors like SKM, have updated these calculation procedures.
    b. Don’t be surprised if study costs increase. There will be more data collection to be conducted and more detailed calculation scenarios to work through.
  2. Ensure you have Reduced Energy Let-Through (RELT) devices in place. Not only is this a code requirement (NEC 240.87), but it’s also just a good idea. This can be achieved through ‘maintenance mode’  switches that change the settings of your breakers while workers are interacting with energized equipment.
  3. Decrease the exposure to incident energy through remote tracking and/or remote switching devices.

If you have questions about the new calculations or need to update your arc flash study contact us at 1-800-827-1662.