Arc Flash Incident Energy calculation dependence on voltage level

[philly]

I've always understood that Incident Energy was a function of the arcing fault current and how long that arcing fault current takes to clear based on the protective device (assuming a fixed distance). I'm curious thogh what role the voltage level plays into the IE calculation? I dont believe the equations used in 1584 take voltage into account?


I've seen several cases where the IE at the 480V level is far worse than at the 4.16kV level. Sometimes this may be due to a faster clearing time for the 480V location but I have seen incoming service entrances that had no upstream protective device to relay on and therefore capped the calculation at 2seconds. For these cases with both the 480V and 4.16kV calculations capped at 2 seconds I've seen that the 480V locations have provided worst case results. Ist this strictly a function of the fault current (more fault current at 480V) than any voltage dependence?



Thanks

 

[ron]

Voltage is in the formula. http://www.arcadvisor.com/arcflash/ieee1584_procedure.html

It needs to be because a lower voltage will impact the ability to sustain the arc.

 

[GoldDigger]

Voltage is in the formula. http://www.arcadvisor.com/arcflash/ieee1584_procedure.html

It needs to be because a lower voltage will impact the ability to sustain the arc.

And for a sustained arc, one term of the energy in the first formula is proportional to the gap length, which in turn effectively determines the voltage which will be seen across the arc, with the current being limited by other impedances upstream.
Even in an arc, P = I*V.