Using MV transformer internal fusing in arc fault energy calculations, pro or con?

[pv_n00b]

When doing an arc fault study of a circuit that has an MV transformer with a LV secondary upstream is it considered acceptable to rely on the internal transformer fusing for arc fault clearing? This would be with the standard expulsion and current limiting fusing in the MV transformer.
I have not been relying on them since I consider them to be for transformer protection only. But the question has come up as to what the industry practice is.

 

[David Castor]

There's nothing wrong with considering the effect of the internal fusing if you know the size and type. But for a fault on the low side, this high side fusing will generally be slow. The fuse just operates on current magnitude, it doesn't know where the fault is.

 

[JoeStillman]

When I do arc-flash energy calculations, I find that fuses upstream of the transformer make a big difference in the incident energy downstream of it. Its a deciding factor whether you get a red sticker or just an orange one.

 

[ron]

No reason not to include it. If the protection curve actually protects, then let it work on the calculation.

They are generally slow, but if it helps not extending into the 2 second cutoff, then good.