Arc flash: risk and PPE
IEC 61482-1-2 box test class check (APC 1 / APC 2) by the DGUV 203-077 energy method
- where
- expected arc energy (kJ)
- normalised arc power
- nominal system voltage (V)
- maximum three-phase prospective short-circuit current (kA)
- arc duration (s)
- protection level of the class at distance a (kJ)
- transmission factor
- working distance (mm)
- mean arc energy of the box test class (kJ)
Explain this equation
Checks whether IEC 61482-1-2 box-tested clothing (APC 1 or APC 2) is adequate, using the energy method of DGUV Information 203-077.
Warc is the expected arc energy: kP is the arc power as a fraction of the short-circuit power √3 × Un × Ik, and tk the arc duration from the protection. Wtest is the mean arc energy in the box test (168 kJ for APC 1, 320 kJ for APC 2) at 300 mm.
The protection level scales with (a/300)² because heat spreads over a larger area further away. kT allows for how enclosed the arc is: 1 for a small box like the test, higher for open arcs, which radiate less energy towards the worker.
Sense check: 400 V, 10 kA, kP 0.29 and 0.25 s give about 500 kJ, more than APC 2 at 300 mm; at 450 mm the APC 2 level rises to 720 kJ.
Watch out: the box-test class is a pass or fail level, not an ATPV, and the two are not interchangeable.
European box-test approach: compares the expected arc energy with the energy that IEC 61482-1-2 Class 1 (4 kA) and Class 2 (7 kA) clothing has been tested against, adjusted for working distance and how enclosed the arc is.
Enter your values to see the result.
Good to know
W1 and W2 are the APC 1 and APC 2 protection levels (test arc energies 168 kJ and 320 kJ at 300 mm) scaled to the working distance a and the transmission factor kT. IEC 61482-1-2 tests garments with a directed arc in a small box at 400 V a.c., 500 ms, specimens 300 mm from the arc axis, prospective current 4 kA (APC 1) or 7 kA (APC 2). DGUV 203-077 gives the mean test arc energies as 168 kJ and 320 kJ (incident energies about 146 and 427 kJ/m², roughly 3.5 and 10 cal/cm²). kP is the arc power as a fraction of the short-circuit power; DGUV gives a worst-case value of about 0.29/(R/X)^0.17 and lower values for small electrode gaps. Read tk from the protection at the minimum arcing current (kB × Ik3min, with kB = 0.5 at LV as the worst case, 1 at HV). The pass/fail result of the box test does not give an ATPV, and the two systems should not be converted into each other.
Common mistake
Equating APC 1 or 2 with an ATPV in cal/cm², or using the box-test class at a working distance shorter than 300 mm.
Limits
Simplified energy method of DGUV Information 203-077 for systems up to 110 kV a.c.; mainly used for LV. kP and kT are judgement values from that guide; the test energies are mean values with a tolerance. UK duty: under the Electricity at Work Regulations 1989 work on or near live conductors is allowed only where reg 14 is met (unreasonable to make dead, reasonable to work live, suitable precautions); regs 12 and 13 require isolation and precautions for dead working, and reg 4(4) requires suitable protective equipment. HSE HSG85 and your DNO or company safety rules (ENA-based distribution safety rules) take precedence. Apply the hierarchy of controls: de-energise first, then engineering controls (faster protection, maintenance switches, remote racking/operation, arc-resistant switchgear), then distance and procedures; arc-rated PPE is the last line of defence.
Sources
- IEC 61482-1-2:2014 Live working – Protective clothing against the thermal hazards of an electric arc – Part 1-2: Box test (APC 1 and APC 2)
- DGUV Information 203-077 Thermal hazards from electric fault arcs: guide to the selection of PPE (English edition 2021)
- IEC 61482-1-1:2019 Live working – Protective clothing against the thermal hazards of an electric arc – Part 1-1: Open arc method (ATPV, EBT, ELIM)
- The Electricity at Work Regulations 1989 (SI 1989/635), regulations 4, 12, 13 and 14
For competent high-voltage engineers. Results are calculations from the published methods shown and depend entirely on the data you enter. They are not a substitute for a system study, manufacturer data, the applicable standards and Engineering Recommendations, or your organisation’s safety rules. Never use a result to justify working on or near live HV equipment.