LV Arc Flash & Fault Level Lab
Work out the prospective fault current at an LV board from the transformer and cable, then the arcing current, incident energy and arc flash boundary with the IEEE 1584-2018 model for 208 to 600 V. See how the protection clearing time drives the energy, pick the PPE rating and print the warning label.
How to use: pick the equipment type to load typical gap, distance and enclosure size, then set the source and the protective device. Tap i for help on any input.
1. Inputs
2. Arc flash results
Warning label, a 3D view of the boundary around the board and how the energy grows with clearing time.
3. Checks
4. Two arcing current cases
IEEE 1584-2018 checks both the full arcing current and the reduced one, because a lower current can trip the device slower.
5. PPE rating bands (NFPA 70E style)
6. How it works
Fault level
The bolted three phase fault current at the board comes from the transformer impedance plus the cable impedance: I = V / (√3 × Z). Close to a large transformer it is high, at the end of a long cable it drops quickly.
Arcing current and the reduced case
An arc has resistance, so the arcing current is lower than the bolted fault current. IEEE 1584-2018 also works out a reduced arcing current using a variation factor. The protection may be slower at the lower current, so both cases are checked and the higher energy is used.
Incident energy and boundary
Incident energy rises in direct proportion to the clearing time, and falls with distance. The arc flash boundary is the distance at which the energy drops to 1.2 cal/cm², the onset of a second degree burn on bare skin. Electrode configuration and enclosure size matter: VCBB and HCB push energy out of the box towards the worker.
How to cut the energy
Faster clearing is the biggest lever: an instantaneous setting, a maintenance switch (energy reducing maintenance setting), zone selective interlocking or arc flash relays with light sensors. Remote racking and working from further away help too.
Learning tool using the published IEEE 1584-2018 equations for 208 to 600 V. A formal arc flash study needs the full network model and coordinated device curves from software. Verify before labelling real equipment.