In the case of locations being energized by multiple feeders, it is necessary to determine the portion of the total arc current passing through each protective device to determine the clearing time for each device. The overcurrent protective device determines the arc duration. The portion of the arcing current flowing through The total arcing current at the point of concern and the portion of that current passing through the upstream protective device(s) must be determined. Therefore, the maximum and minimum short-circuit are both necessary to be considered. Despite the maximum short-circuit is usually considered as worst case, the less arcing current leads to often significantly longer fault clearing times which can results in higher incident energy. Step 4: Calculate the arcing currentĪrcing current is usually less than bolted fault currents however the arcing current is close to bolted fault current for HV. This advancement happens within a few cycles. Arcing faults in devices or air that begin as line-to-ground faults, can also very rapidly step up into 3-phase faults as the air ionizes across phases. However, in most cases three phase short circuit currents typically give the greatest possible short circuit energy and can be considered as the worst-case. The single-phase short-circuit current is used to conduct the single-phase arc flash calculation. The three phase and single-phase short-circuit currents need to be considered. The calculation should take into account the system data and modes of operation. Step 3: Determine the bolted fault currentsĬalculate the short-circuit current.

Shutdown or start-up situation with all motors in an off condition – reduced fault contribution.

Separately derived sources (generators) – minimum number on line.

Separately derived sources (generators) – maximum capacity on line.Utility system normal switching configured for minimum possible fault megavolt amperes.Utility system normal switching configured for maximum possible fault megavolt amperes.Generators running in parallel with the utility supply or in standby.MCC with one or two feeders, one or both energized.Unit substation with two transformers with secondary tie opened or closed.Unit substation with one or two primary feeders.Utility interface substation secondary bus tie circuit breaker open or closed.There are several examples of mode of operation from IEEE1584-2018: The short-circuit current in ‘worst condition’ is supposed to be considered for further arcing current calculations. Step 2: Determine the modes/arrangements of operationĭetermine the available short-circuit current for all modes of operation that provides both the maximum and minimum available short-circuit current. Incident energy level for determining custom arc flash boundarystudy.Enclosure dimension – The height, width and depth of equipment enclosure.Electrode configuration – The orientation and arrangement of the electrodes.Working distance – The distance between the potential arc source and the face and chest of the worker performing the task.Equipment data for incident energy and arc flash boundary.Protective device data for determining the arc duration, such as rating, TCC, device settings, etc.System data for short-circuit calculations, such as nominal voltage, impedance, X/R ratio, etc.The main steps for performing arc flash study are as follows: Step 1 –Collect system, protective device, and equipment data Note IEEE Std 1584 does not provide recommendations for PPE to mitigate arc flash hazards. The results of the study will document the incident energy analysis and may be used by workers as part of an overall electrical safety risk assessment. The main outcomes of the arc flash hazard study calculation are the arc flash boundary and the arc flash incident energy at defined working distances from the arcing source for selected locations in the electrical system. This Standard provides empirical equations which are derived (extrapolated) from models based on statistical analysis of test measurements involving three-phase tests at 600 V with fault currents from 16-50 kA.

The latest IEEE Std 1584-2018 provides an arc flash study procedure which we have consolidated into 8 steps.

Arc flash boundary calculator