V - system voltage (kV)
Ibf - bolted three phase fault current (kA)
Ia - arcing current (kA)
E - incident energy (J/cm2)
EB - incident energy at boundary distance (J/cm2)
En - normalized incident energy (J/cm2)\
t - arcing time (s)
D - distance from arc to person (mm)
CB - distance of boundary from arc point (mm)
Notes:
- EB can be set at 5.0 J/cm2 for bare skin or at the rating of any proposed PPE.
- The limit of 5.0 J/cm2 is that at which a person is likely to receive second degree burns.
- To convert J/cm2 to cal/cm2 multiply by 0.239
| Gap and distance factors |
Voltage (kV) |
Equipment Type |
Typical gap
between
conductors (mm) |
Distance
factor,
x |
0.208 - 1
|
Open Air |
10-40 |
2.000 |
| Switchgear |
32 |
1.473 |
| MCC and Panels |
25 |
1.641 |
| Cable |
13 |
2.000 |
| >1 - 5 |
Open Air |
102 |
2.000 |
| Switchgear |
13-102 |
0.973 |
| Cables |
13 |
2.000 |
| >5 -15 |
Open Air |
13-153 |
2.000 |
| Switchgear |
153 |
0.973 |
| Cables |
13 |
2.000 |
For a more detailed explanation of the calculation, please see: Arc Flash Calculations Post