Enter a value in cal/cm^2 to determine arc flash protection boundary (FPB) distance at that Incident Energy. The Incident Energy of 1.2 cal/cm^2 for bare skin is used in determining Flash Protection Boundary in IEEE 1584 and NFPA 70E standards. Minimum of 0.3 cal/cm^2, maximum of 3 cal/cm^2 accepted in this online DC arc flash calculator.

Available Short Circuit current for the range of 2kA to 50kA at the point where work is to be performed is entered into this box in kA. Example: if 42,357 amps are available, enter 42.357 into this box. If 16,000 amps are available, enter 16 into this box. Check an example showing how to calculate DC short circuit current in AC / DC mine power system.

DC System Voltage for the range of 40 Vdc to 500 Vdc is entered into the box in Volts.

Currently, the online DC arc calculator is limited to copper electrodes only. It was found [1] that, when current is not too low, voltage of an arc in open air with copper electrodes is determined by the anode, cathode drops of approx 30V, and positive column voltage drop of the order of 10V/cm. Consider ARCAD DC Arc Flash Analysis and Labeling Software capable to solve arc flash equations for a variety of different electrode materials including copper, aluminum, steel and their combination.

Distance between electrodes. It determines voltage drop across positive column. The voltage drop across the positive column is proportional to its length, a few volts per centimeter. Leave this field blank if gap value is not known or spacing between anode and cathode is anticipated to increase by the separation of the contacts. If this field has been left blank, the calculator will determine maximum energy that can be released by an arc for given circuit parameters and calculate incident energy and flash protection boundary based on it.

Measure of DC circuit inductance. Circuit Time Constant is used to determine arc duration based on circuit protective device time-current characteristics under DC transient conditions. Published fuse time-current characteristics show the time required for a fuse to clear the fault under different RMS load currents. However, under DC short circuit conditions, the effective RMS current is much different from the instantaneous current under DC short circuit conditions [2] and the published fuse AC time-current characteristics cannot be used for DC applications. The time current characteristic curve that will aplly for a specific DC application depends on the specific time constant. When circuit time constant is specified within 0 to 50 miliseconds range, the calculator will take care of converting a time current curve to DC curve and determine arc duration based on it and on the amount of arcing current.

Circuit protection device clearing the fault. The online DC arc flash calculator list of protective devices is limited to Time Delay Class J and Class L 100A to 2000A rated one's manufacturer fuses only . The results with other manufacturers fuses of the same class should be similar. If you have a different device protecting your DC system, consider ARCAD DC Arc Flash Analysis and Labeling Software featuring expandable circuit protective device library.

The calculator determines arc duration based on time-current characteristics of circuit protection device clearing the fault and circuit time constant. If the arcing fault current is above the total clearing time at the bottom of the curve (0.01 seconds) and circuit time constant equals 0 ( the case of 100% resistive circuit ), the calculator uses 0.01 seconds for the time. The upper limit for arc duration has been set up to 2 seconds. It's usually assumed that the outer limit for the arcing time is no more than 2 seconds. Although this is not a hard and fast rule, it accounts for the likelihood that the arcing material in an arcing field will likely be either burned off or expelled by the force of the blast. In any case, this would extinguish the arc event. Also, IEEE 1584 states "If the time is longer than two seconds, consider how long a person is likely to remain in the location of the arc flash. It is likely that a person exposed to an arc flash will move away quickly if it is physically possible and two seconds is a reasonable maximum time for calculations." [ Annex B page 76]. [3]

Flash protection boundary: An approach limit at a distance from exposed live parts within which a person could receive a second-degree burn if an electrical arc flash were to occur. Flame resistant personal protection equipment (PPE) must be worn by anyone within the flash protection boundary.

The amount of energy impressed on a surface, a certain distance from the source, generated during an electrical arc event. This energy is generally expressed in calories/cm². The surface of concern impressed on is the worker s body, particularly the head and trunk. Incident energy is calculated using variables such as available fault current, system voltage, expected arcing fault duration and the worker s distance from the arc. The data obtained from the calculations is used to select the appropriate flame resistant (FR) PPE, just as voltage level is used to select a class of rubber gloves.

This is the minimum level of Personal Protective Equipment in calories per centimeter squared, as evaluated in IEEE Standard 1584, with the intent to protect the worker from the thermal effects of the arc flash at 18 inches from the source of the arc.
 

Min Incident Energy, cal/cm^2	Max Incident Energy, cal/cm^2	Risk Category	Required Min Rating of PPE, cal/cm^2
0	Eb*	0
Eb* + 0.001	4	1	4
4.001	8	2	8
8.001	25	3	25
25.001	40	4	40
40.001	and above	Not Available	N/A

* Eb is Incident Energy to second degree burn for bare skin exposure.

References: