Set Arc-Flash Values

The Set Arc-Flash Values command is used to define additional information for panels and other one-line devices to allow arc-flash calculations to be performed.

To specify the arc-flash information, go to

DM Electrical->One-Line Devices->Set Arc-Flash Values

Arc-Flash Dialog Box

One-Line Devices--Arc-Flash dialog box

Each one-line device is listed as a row in the grid. The bold columns are values calculated. You are responsible for filling in the other values.

Device: The one-line device. Devices are listed in a tree based upon which devices are fed from other devices.

Calculate Arc-Flash: Whether or not arc-flash is calculated for the device. Devices that are 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, devices with voltages less than 208V do not need arc-flash calculations performed. This box has to be manually unchecked for devices below 208V.

Voltage: The voltage of the device. The voltage determines the arc-flash calculation method that is used. The voltage is set when you create the one-line device. It cannot be changed in this dialog box. To change the voltage, use the Edit Existing One-Line Device command to edit the device.

Equipment Type: The equipment type as described in IEEE Std 1584-2002 Table 4. The type of equipment selected sets a distance ‘x’ factor. The ‘x’ factor is used as an exponent in the calculation. Higher ‘x’ values result in higher incident energy values. The following list displays the ‘x’ factor for each type of equipment for voltages between 208V and 1,000V.

Equipment Type

x

Switchgear

1.473

MCC

1.641

Panels

1.641

Open Air

2.0

Cable

2.0

For voltages below 208V and above 1000V, consult IEEE Std 1584-2002. The ‘x’ values are slightly different, but the relative orderings are the same (switchgear is the lowest, open air and cable are the highest).

Configuration Type: Whether the device is enclosed or not. Enclosed devices reflect the arc-flash toward the worker, resulting in higher incident energy values. Most panels and other devices inside buildings should be set to Box.

Open: no enclosure, lower incident energy
Box: enclosed equipment, higher incident energy

Grounding: The type of grounding on the device. Grounded devices have lower incident energy values.

Grounded: lower incident energy
Ungrounded and high resistance grounded systems: higher incident energy

Gap Between Conductors: The gap between the conductors. The most accurate calculation can be used when the gap between conductors is between 13 mm and 152 mm. Within that range, the smaller the gap, the higher the incident energy. If possible, set the gap based the manufacturer’s specifications. Typical gaps between conductors for devices between 208V and 1,000V are listed in IEEE Std 1584-2002 Table 4.

Equipment Type

Gap Between Conductors

MCC

25 mm

Panels

25 mm

Switchgear

32 mm

Open Air

10-40 mm

Cable

13 mm

For voltages below 208V and above 1000V, consult IEEE Std 1584-2002.

Working Distance: The distance from the possible arc point to the person working on the device. It includes both the distance from the device to the worker and the distance from the front of the equipment inside to where the arc flash would occur.

The incident energy will be calculated at this distance from the device. The farther away from the device, the lower the incident energy. Any part of the body closer to the device than this distance will be exposed to higher incident energy than is calculated. If possible, set the working distance based upon the actual dimensions of the equipment. Typical working distances are given in IEEE Std 1584-2002 Table 3.

Equipment Type

Typical Working Distance

Low-voltage switchgear

610 mm

Low-voltage MCCs

455 mm

Low-voltage panelboards

455 mm

Cable

455 mm

Other

To be determined in field

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 the arc-flash calculations assume the equipment and the fault are three-phase. For single-phase equipment, the calculations provide conservative results.

Arcing Current, 100% & 85%: The predicted three-phase arcing current used to determine the operating time for the protective devices. For voltages less than 15,000V, the 100% column is calculated based on the values to the left in the grid. The 85% column is based upon the 100% column.

For voltages greater than 15,000V, the arcing current is equal to the fault current.

Arcing Time, 100% and 85%: The duration of the arc-flash 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 normally be found on their website.

You are responsible for entering two values, one for the arcing time at 100% of the arcing current, and the other for the arcing time at 85% of the current.

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 at 100% of the arcing current value and at 85% of the arcing current value. The greater of the two incident energy values is used to determine the PPE required for the device.

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 listed. If only the melting time is listed, for greater than 0.3 seconds add 10%, otherwise add 15% to the time.

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

Incident Energy, 100% and 85% Arcing Current: The total incident energy is calculated based upon the arcing current, duration, and working distance.

Required PPE: Personal Protection Equipment (PPE) rating required to work on the device. The rating is based upon the larger of the two calculated incident energy values.NFPA 70E 2012 Table 130.7(C)(16) lists the minimum arc rating for clothing in cal/cm². All of the calculations are done in J/cm². Both values are listed below.

Hazard / Risk Category

Arc Rating Range

0

0-5 J/cm²

0-1.2 cal/cm²

1

4-16.7 J/cm²

1.2-4 cal/cm²

2

16.7-33.5 J/cm²

4-8 cal/cm²

3

33.5-104.6 J/cm²

8-25 cal/cm²

4

104.6-209.2 J/cm²

5-40 cal/cm²

X

> 209.2 J/cm²

> 40 cal/cm²

Arc-Flash-Protection Boundary Energy: The arc-flash-protection boundary is the approach limit for unprotected workers. You can specify the energy value. This is the amount of energy that will be delivered at the boundary distance. The default energy value of 5.0 J/cm² will limit burns to an unprotected worker to second degree during an arc-flash incident.

Arc-Flash-Protection Boundary Distance: The boundary distance is calculated based upon the specified Arc-Flash Protection Boundary Energy value in millimeters.


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