Arc-Flash Maximum Boundary

[jdhaze]

Is there a table showing the maximum flash hazard boundary for the different hazard levels? What I'm trying to say is @ 1.2 cal/cm2 the distance is X, at 4 cal/cm2 the distance is Y, 8 cal....25cal.......?

thanks

 

[GoldDigger]

Is there a table showing the maximum flash hazard boundary for the different hazard levels? What I'm trying to say is @ 1.2 cal/cm2 the distance is X, at 4 cal/cm2 the distance is Y, 8 cal....25cal.......?

thanks

Unfortunately not as simple as that in real life. For a point source of energy (like a light bulb or a short arc) the energy per unit area falls off as one over the square of the distance. So at twice the distance the cal/cm2 will be 1/4. But if the energy source is not a point (say an arc uniform over a 2' by 2' area, for example) the energy can be focused in a particular direction and not drop off as fast over short (order of 5 feet) distances. And at high voltages the arc itself can extend over a variable region of space.

You can generalize more accurately when large distances from the arc flash (tens of feet) are involved, but I am not sure how useful that would be, since you would then be in the range of remote actuation anyway.

 

[jdhaze]

Arc-Flash Maximum Boundary

Let see if I can understand. It sounds like you are bringing up the differences between open air flash vs. 'arc in a box'. Your other statement indicates that if you have 1.2cal/cm2 @ 18", the maximum arc-flash boundary will change if it is 480v vs. 4160v, is this an accurate assessment?

 

[GoldDigger]

Let see if I can understand. It sounds like you are bringing up the differences between open air flash vs. 'arc in a box'. Your other statement indicates that if you have 1.2cal/cm2 @ 18", the maximum arc-flash boundary will change if it is 480v vs. 4160v, is this an accurate assessment?

That is an accurate assessment of what I said. I make no claim that what I said is accurate, and will wait for one of the regulars who deal in this all the time to comment. I would however correct "will change" to "may change"