Arc-Flash Settings

The Arc-Flash Settings dialog box is used to manage the variables that affect arc-flash calculations for the selected distribution equipment.

distribution-equipment--arc-flash-settings-dialog-box

Voltage: The voltage of the distribution equipment. The voltage determines the arc-flash calculation method that is used.

Calculate Arc-Flash: Whether arc-flash is calculated for the distribution equipment. Equipment that is not calculated will not be displayed in the arc-flash schedule on the drawing and will not have stickers created. Because it is difficult to sustain an arc-flash below 208V, equipment with voltages below 208V do not need arc-flash calculations performed and will have this option set to No by default.

Electrode Configuration: The electrode configuration as described in IEEE Std 1584-2018 Table 9. Horizontal configurations generally have higher incident energy than vertical configurations. Enclosed configurations generally have higher incident energy than open configurations. Most distribution equipment inside buildings should be set to an enclosed configuration. See the Electrode Configurations for Arc-Flash Calculations article in the knowledge base for more information about these configurations.

Unknown: This setting should be used if the electrode configuration is unknown. The calculations provide conservative results.
Vertical conductors or electrodes inside a metal box or enclosure: This setting has the lowest incident energy among enclosed configurations.
Vertical conductors or electrodes terminated in an insulating barrier inside a metal box or enclosure: This setting has a lower incident energy than Horizontal conductors or electrodes inside a metal box or enclosure, but higher than Vertical conductors or electrodes inside a metal box or enclosure.
Horizontal conductors or electrodes inside a metal box or enclosure: This setting has the highest incident energy among all configurations.
Vertical conductors or electrodes in open air: This setting has the lowest incident energy among all configurations.
Horizontal conductors or electrodes in open air: This setting has the highest incident energy among open configurations.

Enclosure Size: The dimensions of the enclosure. The smaller the enclosure, the higher the incident energy. The size of the enclosure does not affect arcing current and arcing times.

Unknown: This setting should be used if the dimensions are unknown. The calculations will be based upon a 20" x 20" x 9" enclosure.
Known: Enter values for the Enclosure Width and Enclosure Height fields and set Enclosure Depth manually. If possible, set the dimensions based upon the manufacturer's specifications. Typical enclosure dimensions are listed in IEEE Std 1584-2018 Table 8. Dimensions for equipment between 208V and 600V are listed in the table below.

Equipment Type

Enclosure Size

(H x W x D)

Switchgear

20" x 20" x 20"

MCC

14" x 12" x 8"

Panel

14" x 12" x 8"

Cable Junction Box

14" x 12" x 8"

Enclosure Height: The height of the enclosure.

Enclosure Width: The width of the enclosure.

Enclosure Depth: The depth of the enclosure.

Typical: The calculations will be based upon a depth greater than 8".
Shallow: The calculations will be based upon a depth of 8" or less.
Specific: Enter a value for the Enclosure Depth field manually.

Gap Between Conductors: The gap between the conductors. For devices between 208V and 600V, the most accurate calculation can be used when the gap between conductors is between 0.25" and 3". Within that range, the larger the gap, the higher the incident energy. For gaps outside this range, the calculations provide conservative results.

Unknown: This setting should be used if the gap is unknown. For devices between 208V and 600V, the calculations will be based upon a gap of 3". For devices above 600V, the calculations will be based upon a gap of 10".
Known: Enter a value for the Gap Between Conductors manually. If possible, set the gap based upon the manufacturer’s specifications. Typical gaps between conductors are listed in IEEE Std 1584-2018 Table 8. Gaps for devices between 208V and 600V are listed in the table below.

Equipment Type

Gap Between Conductors

Switchgear

1.25"

MCC

1"

Panel

1"

Cable Junction Box

0.5"

Working Distance: The distance from the possible arc point to the torso of the person working on the distribution equipment. The incident energy will be calculated at this distance from the equipment. The farther away from the equipment, the lower the incident energy. Any part of the body closer to the equipment than this distance will be exposed to higher incident energy than is calculated.

Unknown: This setting should be used if the working distance is unknown. The calculations will be based upon a working distance of 12".
Known: Enter a value for the Working Distance manually.If possible, set the working distance based upon the actual dimensions of the equipment. Typical working distances are listed in IEEE Std 1584-2018 Table 10. Working distances for equipment between 208V and 600V are listed in the table below.

Equipment Type

Working Distance

Switchgear

24"

MCC

18"

Panel

18"

Cable Junction Box

18"

Bolted Fault Current: The bolted fault current is the fault at the equipment. This value is calculated based upon the other settings in your project. All of the arc-flash calculations assume the equipment and the fault are three-phase. For single-phase equipment, the calculations provide conservative results. If the fault is less than 500 A or greater than 106,000 A, the calculations provide conservative results.

Arcing Current, Maximum and Reduced: The predicted three-phase arcing current used to determine the operating time for the protective devices. The maximum arcing current is the upper limit for the equipment. The reduced arcing current is the lower limit for the equipment.

These values are calculated based upon ranges specified in IEEE Std 1584-2018. If any of the following values for the equipment are outside the listed range, the calculation will be performed using the Lee Method:

Voltage: 208V to 15,000V
Bolted Fault Current: 500A to 106,000A at 208V to 600V; 200A to 65,000A above 600V
Gap Between Conductors: 0.25" to 3" at 208V to 600V; 0.75" to 10" above 600V

If the Lee Method is used, only the Arcing Current, Maximum will be calculated.

Manually Set Arcing Time: Whether the arcing times are entered manually or set automatically based upon time-current curves set in the Select Curve dialog box.

Yes: Enter values for the arcing times and Arcing Time Basis field manually.
No: The arcing times and Arcing Time Basis field will be set automatically based upon the next protective device that is upstream of the equipment. If an upstream protective device has not been set, the arcing times will be set to 2 seconds and the Arcing Time Basis will display "UNKNOWN BREAKER" for the protective device.

Duration at Maximum Arcing Current and Reduced Arcing Current: The duration of the arc-flash at the Maximum Arcing Current and Reduced Arcing Current. The duration has a significant impact on the incident energy in seconds. The longer you are exposed to the flash, the more intense the burn. The arcing time is based upon the time-current curve for the specific breaker you are using. These values are provided by the manufacturer and can typically be found on their website.

The incident energy is a function of the arcing current and the duration. Lower arcing currents that take longer to close the breaker can result in higher incident energy values than high arcing currents. To account for this, incident energy is calculated using both the Maximum Arcing Current and Reduced Arcing Current.

Fuses must be handled differently from breakers. The time-current curves for fuses may include both melting and clearing times. Use the clearing time if it is provided. If only the melting time is provided, you can approximate the clearing time by adding 10% to the melting time if it is greater than 0.3 seconds, or 15% if it is less than 0.3 seconds.

If the arcing current is above the total clearing time at the bottom of the curve (0.01 seconds), use 0.01 seconds.

Arcing Time Basis: The time-current curve the arcing times are based upon.The value of this setting can be displayed on the arc-flash schedule and one-line diagram. It is for informational purposes only and is not otherwise used.

Incident Energy, Maximum Arcing Current and Reduced Arcing Current: The total incident energy based upon the arcing current, arcing times, and working distance.

Arc-Flash Boundary Distance: The limited approach boundary for unprotected workers. At this distance, the harm inflicted upon an unprotected worker during an arc-flash incident will be limited to second-degree burns.


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