Arc Flash Hazard Options

You can select any of the following standards for calculation method.

• IEEE 1584-2018

This method is based on the IEEE 1584-2018 Guide For Performing Arc Flash Hazard Calculations, a revision of the original publication in 2002. The arc flash hazard calculations are dependent upon equipment voltage, bolted fault current, arc time, electrode gap, electrode configuration, and enclosure size. Selection of the calculation method for systems outside of the IEEE model range is available in the Advanced Arc Flash Options. See Advanced Arc Flash Options for more information.

• IEEE 1584-2002

This method is based on the IEEE 1584-2002 Guide For Performing Arc Flash Hazard Calculations and includes amendments 1584a-2004 and 1584b-2011. The arc flash hazard calculations are dependent upon equipment voltage, bolted fault current, arc time, electrode gap, equipment type and system grounding. NFPA 70E-2018 Standard for Electrical Safety in the Workplace references this calculation method in Annex D.4. The Ralph Lee method is applied where system voltage exceeds 15 kV.

• NFPA-70E D.2, D.3 +

In NFPA 70E, Annex D provides summarizes calculation methods available for calculating arc flash boundary and incident energy. These are empirical equations based on arc flash tests. The arc energy is dependent on the variables bolted fault current, arc time, and enclosure type. The Annex references equations from a paper published in 1998 by R. L. Doughty, T. E. Neal and H. L. Floyd, II. Refer to the standard or the original paper for details on the calculation method.

• V7.0 Enhanced

The V7.0 Enhanced equations are based on the IEEE 1584-2002 equations. Close examination of the IEEE 1584-2002 equations revealed that, in a few cases, unexpected results occurred. For example:

• Arc currents could be calculated that were greater than the bolted fault current, specifically at voltages slightly higher than 700 V.
• Incident energy in open air could be more severe than in enclosed switchgear.
• Unexplained discontinuities existed when plotting the results over a range of voltages between the low voltage equations and high voltage equations.

Due to these types of issues, EasyPower developed a set of Enhanced arc flash equations that were similar to the IEEE 1584-2002 equations, but addressed these and other concerns. Based on engineering judgments and comparison with test data from the industry, the results from the Enhanced equations appear to be more reasonable than the IEEE 1584-2002 over a wide range of bolted fault currents and system voltages. However, users should be aware that the Enhanced models cannot be guaranteed to be more accurate than the IEEE 1584-2002. The Enhanced method is intended to be a tool used to assist in the selection of protective clothing for workers who may be exposed to arc flash.

• V6.0 Enhanced

The V6.0 Enhanced equations pre-dated the V7.0 Enhanced equations. If you choose to use the Enhanced equations, it is recommended that the V7.0 Enhanced be used. The V6.0 Enhanced equations are included for archival purposes only.

Worst-Case Arc Flash Hazards

EasyPower obtains the arcing time from the upstream protective device of the faulted bus. The program uses the coordination feature PowerProtector™ to calculate the trip time for the estimated fault current passing through the protective device. This is the most accurate method. This option works only if you have the PowerProtector™ feature included in your EasyPower software.

Select one of the options to evaluate the arc flash hazard results for any bus in the following ways:

• Including Main: This option yields the results for fault on the bus bar itself. If a main breaker or fuse protects the bus and this breaker or fuse is connected to the bus, then the arcing time would be equal to the trip time for this main device. If a worker is working on the bus or on the load side of the main breaker/fuse, then this option of output applies. However, this option of output should not be used if energized work is required on the line side of the main breaker/fuse.
• Excluding Main: This option yields the results for fault on the bus bar excluding the tripping effect of the main breaker. This option of output is applicable to energized work on the line side of the main breaker of the bus. The remote upstream trip device is used to calculate the arcing time.

Note: Panels typically have the main breaker, bus bar and feeder breakers housed inside the same enclosure. Opening the front cover would expose a worker to arc on the line side of the main breaker. To simulate this hazard, select the Excluding Main option, since the device to interrupt faults would have to be an upstream device.

• Both (Incl & Excl Main): This option yields the results for fault on the bus bar as well as on the line side of the main breaker/fuse, provided the bus has a main breaker/fuse attached on the upstream side.
• Detailed: This option evaluates the results for the bus bar as well as the load side terminals of all protective devices attached to and downstream from the bus.

This option is not applicable to IEEE 1584-2018.

IEEE 1584-2002 recommends using two scenarios – one with 100% of estimated arc current and the other with 85% of estimated arc current. This is due to the fact that arc currents may be random and usually vary by some proportion about the estimated value. For inverse-time over-current characteristics of protective devices, the arcing time is greater for smaller currents than it is for larger currents. Since the incident energy of arc faults is more sensitive to arcing time than it is to arc currents, it is necessary to obtain a more accurate arcing time. IEEE 1584 proposes taking 85% of the initial estimate of the arc current.

EasyPower enables you to consider two scenarios of arc currents. EasyPower calculates both scenario and automatically reports the worst case of incident energy, thus providing conservative results.

The IEEE 1584 recommended 100% and 85% of arc current are default values. You may change these ratios by typing in the fields or using the buttons to increase or decrease the values.

When 100% or the upper value yields greater arc flash incident energy, then the text results are displayed in black in the Arc Flash Report spreadsheet. When 85% or the lower value yields greater incident energy, the text is displayed in pink.

The Max Time is the maximum time that the program uses to calculate the incident energy. If the trip time calculated as per device TCC is less than the specified maximum time, then the device trip time is used. If the device trip time exceeds the specified maximum time, then the Max Time value is used. The default maximum time is 1000 seconds.

Specify the fault current used during arc flash calculations. Select between Momentary, Interrupting, and 30 Cycle fault currents or the Integrated method.

See The Integrated Method for more information about this method.

You can select the units for working distance from any of the following. This also affects the arc flash boundary.

• Inches
• Feet
• Inches/Feet: Displays results in both inches and feet.
• mm
• Meter
• mm/Meter: Displays results in both mm and meters.

You can specify separate working distances for open air and enclosed space. Select the appropriate choice to view or edit the values in the spreadsheet. Typically for medium voltage, switches and fuses at open air may be operated from a greater distance.

In the Enclosed table, there are separate working distances for switchgear. This enables you to specify a different working distance for switchgear than for other types of equipment.

You can specify whether you want incident energy displayed in calories or joules per square centimeter.

Check this box to obtain a report of buses that exceed the arc flash threshold incident energies specified in the options. You can specify any incident energy as the threshold for various voltage levels by typing in the values in the spreadsheet in the Arc Flash Hazard options. All equipment exceeding the hazard thresholds will be displayed in red on the one-line.

For every voltage level you can specify the threshold incident energy. Equipment with incident energies exceeding the threshold values will be highlighted in red in the one-line output and they will be reported in the Arc Flash Threshold Report. This provides instant notification of a danger condition. All equipment with incident energies exceeding the threshold values are displayed in red on the one-line.

For every voltage level, you can specify up to five working distances for which the incident energy will be provided in the Arc Flash Report. In the one-line output, results will be shown only for the shortest working distance, which has the highest incident energy.