Arc flash analysis vs. available fault current analysis

[dneff]

I have been asked to do an available fault current ratings and analysis. The person said it is different from an arc flash analysis:?. What are the differences? Where can I find the requirements and steps for available fault current analysis?

Thank you in advance

 

[jim dungar]

The results from 'available fault current analysis' are effectively the input data for an arc flash analysis.

 

[GoldDigger]

The fault current analysis tells you what the absolute maximum value of current into a bolted fault.
It does not tell you the current that could be developed across an arc with non-zero voltage.
Nor does it tell you how long various current levels could last before an OCPD opens the circuit.
The latter two, among other things, are also inputs to an arc fault analysis, which is a much more expensive engineering effort.
He is saying that you are not expected to do that.

Tapatalk!

 

[dneff]

Thank you both very much. So basically I just need to find I=VA/(E*sqrt(3)*Z) at all panels and transformers, is that correct?

 

[GoldDigger]

You may need to reduce the available fault current based on conductor impedances or the actual primary current from POCO if the simple answer comes out to an unfortunately high number.
That will depend on what the client is willing to pay for and whether there is existing equipment which might be out of compliance with just the conservative (worst case) analysis

Tapatalk!

 

[junkhound]

I have been asked to do an available fault current ratings and analysis

Ah, a flashback to 50 years ago when first asked for such. FWIW, unless you are at the end of a long rural power line, you can pretty much simplify your analysis to the secondary of the distribution transformer and downstream. Your biggest problem is finding the percent reactance of the distribution transformer(s), most likely need to contact poco for that.

FWIW2 just as a reality check, the short circuit current on the 208 V end in an underground facility in North Dakota at the end of a 3 phase rural line on a 13.9kV to 480 V delta to 480/120 delta-wye transformer was only 1980A (still remember that number, had to determine what the positive, negative, and zero sequence voltages and current were also). IIRC, was only a few dozen amps lower if the 35 mile 13.9 kV line was taken into account.

 

[dneff]

Thank you all for the clarification.

 

[graywolf]

You could use tables with this method, if over current device's were tested and cleared within time stated in tables.
Bare in mind this is very conservative method and may require higher level of PPE . Also only applies to listed tasks