Part 1 of the arc flash series. Same fault current, same clearing time — and the incident energy changes from 3.3 to 5.9 cal/cm² just by how the conductors are arranged.
| Equipment | 415 V LV switchgear: gap 32 mm, enclosure 508 × 508 × 508 mm, working distance 610 mm |
| Bolted fault current | 30 kA |
| Clearing time | 100 ms |
VCB: vertical conductors in a box. VCBB: vertical conductors ending in an insulating barrier, which pushes the arc towards the worker. HCB: horizontal conductors pointing out of the box, directing the plasma straight out. IEEE 1584-2018 gives each its own coefficients.
The arc's own impedance limits the current. IEEE 1584-2018 also calculates a reduced arcing current (variation factor) to check slower protection.
| Configuration | E (cal/cm²) | Arc-flash boundary (mm) | Indicative PPE |
|---|---|---|---|
| VCB | 3.29 | 1,146 | Category 1 |
| VCBB | 4.39 | 1,249 | Category 2 |
| HCB | 5.87 | 1,333 | Category 2 |
Choose the configuration that matches the actual bus arrangement where work is done — for example, HCB for horizontal bus bars facing the door or for breaker line-side terminals pointing out. When in doubt, check more than one and use the higher energy.
| Check | Requirement | Actual | Status |
|---|---|---|---|
| VCB | ≤ 4 cal/cm² for Category 1 | 3.29 cal/cm² | ✓ PASS |
| HCB | ≤ 4 cal/cm² for Category 1 | 5.87 cal/cm² | ✗ FAIL |
Key insight: In IEEE 1584-2018 geometry matters as much as current. HCB typically gives the highest energy because the arc plasma is driven towards the worker.
Every input in this example is editable in the live calculator — no signup needed.
Open Arc Flash calculator →Testing showed that electrode orientation and barriers change the energy reaching the worker substantially, which the 2002 edition did not capture.
VCB is the usual default, but many MCC buckets and breaker terminals are better described by VCBB or HCB.