Guidance for Performing Short Circuit Studies as Part of Arc Flash Studies

This week’s question of the week was submitted by a colleague of mine so here goes. - Feel free to submit your questions to me as well!

It is generally understood that the results of a short circuit study are an important component for arc flash calculations/studies.

When it comes to short circuit calculations, there are two main standards used – ANSI/IEEE and IEC. Most (all?) software is based on these standards.

This week’s question is NOT about the specific calculation method but IS about guidance used for performing the short circuit study as part of an arc flash study. i.e. how to perform the study, model the system, source data etc. Since the MAXIMUM short circuit current may not necessarily be the worst case for an arc flash study, there may be a few more considerations that need to be made.

Here is this week’s question:

What guidance do you use for performing a short circuit study?

IEEE 551 (Violet Book)
Other IEEE Colored book (Evolving into the 3000 series)
IEC 60909 / 61363
Company Practices
Software Manufacturer Guidance
IEEE 1584.1 (Specifying Scope and Deliverable Requirements of AF Study)
Internet / Magazine Articles
Something Else
I don’t perform short circuit studies

Select all answers that apply

I checked Something Else as one of the sources used as I refer to Conrad St. Pierre's book which I believe evolved from the original effort on the Violet Book

Great reference! I have it to. Conrad was a legend in the industry.

You forgot an option:

Somethings else:
OSHA 1910.269
IEEE C2

Neither one of these gives a short circuit calculation.

It depends highly on what it's for.

If I'm doing short circuit studies for equipment design and specification purposes, the ANSI (X/R) method is pretty much universal in the United States. Occasionally I will see IEC 60909 show up but that's rare.

If I'm doing it for arc flash studies, then obviously the full Ohm's law (generally IEC-like) method is appropriate since the goal is to determine as low of a short circuit value as possible knowing that the incident energy is maximized in most cases with the lowest reasonable short circuit.

If I'm doing a quick field calculation, I'll just use transformer %Z with the infinite bus assumption and some fudge factors for shielded cable and large motors in keeping with the ANSI method. It's not quite to the decimal but it gives me a reasonable upper limit on short circuit current and is within a few percent of the ANSI method in practice but something I can do on a napkin in the field as a quick estimate when needed.

If there is no chance of doing a proper arc flash study then the tables apply if the purpose is for arc flash, either using the IEEE C2 or NFPA 70E tables.

Thanks! I overlooked that one!

Jim

Please advise how I can order a copy in the UK

I have owned a copy previously however this has vanished and I would like to replace