New to Short Circuit / Arc Flash Study 2

[viper1bw]

Currently I am a completing a EE co-op. My project that I have been assigned is to determine the Arc Flash boundries and PPE requirements for their equipment. I'm a bit thrown to the wolves in this b/c my background has been more of circuit design up until this point.
Some company power info: ( this is for multiple buildings)
Pad-mounted Transformers range from 1000-2500 kVA (12.47kV supply)
34 buslines
operating voltages inside the plant 480v-120v

So far I have done a one line diagram of the electrical for all the buildings. With the researching that I have done to this point, It's my understanding that using the MVA method would be my next step.
Correct me if I am wrong but it's just converting the kVA into MVA 10^3 vs. 10^6
If this is right, would there be an easier method for calculating Short Circuit current in my situation where the vast majority of the voltage is at 480v?

Thanks for any of your help.

 

[rbulsara]

Ok..may be I misunderstood.

To start an arcing event not much current is required, but once an arc is established it could (and it does in most cases) rapidly develop in a fireball and a blast. This is because the inital arc ionizes the air which furhter lowers the fault impdedance and increases the fault current and the cycle continues rapidly growing in a dangerous event.

This is one of the reasons, single phase systems are not evaluated on a 3 phase system, because it is assumed that a single phase arcing fault will quickly develop in a 3 phase fault at any rate.

The knowledge of a short circuit study is necessary to estimate most likely damage (release of incident energy) by an arcing fault at a certain point.

 

[dpc]

Basically, per NFPA 70E and IEEE 1584, at 480 V there is no minimum value of available short circuit current below which you don't need PPE. I think that is where you are trying to go, but you're not going to get there per the current standards. If it's 480V, an arc-flash hazard exists.