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Arc-Flash Settings and Sensitivity (IEEE Std 1584-2002)

Friday, November 9th, 2018

NOTE: This article contains information related to older versions of Design Master Electrical and Design Master Electrical RT. If you are using DM Electrical 8.6+ or DM Electrical RT 1.4+, see Arc-Flash Settings and Sensitivity (IEEE Std 1584-2018).

When calculating arc-flash for a piece of distribution equipment, there are numerous settings you can adjust to change the resulting incident energy values:

  • The equipment type as described in IEEE Std 1584-2002 Table 4
  • Whether the equipment is enclosed or open
  • The type of grounding
  • The size of the gap between conductors
  • The working distance

The size of the change in the incident energy differs for each setting. The tables and charts below illustrate the sensitivity of each setting.

The data is based upon a 480V panel with a bolted fault current of 57,801 A, an arcing time of one cycle (0.0167 seconds), and the default settings.

Equipment Type

The type of equipment does not significantly impact the incident energy. In fact, values do not change at all between the Panel and MCC settings, or between Open Air and Cable.

Equipment Type Incident Energy
(cal/cm2)
Open Air 1.96
Switchgear 1.68
MCC 1.77
Panel 1.77
Cable 1.96

Configuration Type

If the distribution equipment is not enclosed, the incident energy will be roughly half of what it would be for an enclosed piece of equipment.

Configuration Type Incident Energy
(cal/cm2)
Open 0.89
Box 1.77

Grounding

Incident energy is slightly lower if the distribution equipment is grounded. There is no difference if it is ungrounded or part of a high-resistance grounded system.

Grounding Incident Energy
(cal/cm2)
Grounded 1.77
Ungrounded 2.29
High-Resistance Grounded System 2.29

Gap Between Conductors

Incident energy will decrease as the gap increases, but the difference is not significant.

Gap Between Conductors Incident Energy
(cal/cm2)
0.6″ 1.95
1″ 1.77
1.5″ 1.57
2″ 1.39

Working Distance

Working distance is by far the most significant factor when calculating arc-flash. As the working distance decreases, incident energy increases exponentially.

Working Distance Incident Energy
(cal/cm2)
9″ 5.52
12″ 3.44
15″ 2.39
18″ 1.77
21″ 1.37
24″ 1.10

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