RES Technical Corner by Brett Eliasz, PE

For the Electrical article this month I’d like to share a pretty basic way of thinking I fall back on quite often when completing Arc Flash, Short Circuit and Coordination Studies.

My way of thinking relates to a rating system which I see at some big box retail stores. They tend to stick to the terms “good, better and best”.

For many of the Electrical folks out there performing these studies, they know it is quite often just not feasible to obtain every piece of information in an existing electrical system.

For example:

Sometimes, we might have to go from design documents to determine a cable size, which is “good”, but what if the cable has changed throughout the construction process..? Perhaps we actually have as-builts from a contractor which would be “better”, with “best” being a full shut down to get eyes on the cable size actually installed.

Three (3) other characteristics of an electrical system come to mind from IEEE 1584-2018, which is the standard used to complete these calculations:

Electrode Configuration, Enclosure Dimensions and Conductor Gap.

Think about a typical electrical panel board…is the bussing vertical…? Depends…Open and look… What is the dimension of the enclosure?...is there a standard…? Somewhat…measure it… Conductor Gap?...is there a standard…? Not really…measure it…dangerous to obtain…?

I know that the software today does automatically make assumptions for these characteristics. Of course, it gives you the ability to modify them as needed. But you must make sure you select the latest version of IEEE 1584.

If we were to include the assumptions the software makes in our analysis, then I think that would put the results in a “good” category. Perhaps if we field verified some of them and made assumptions on the others then we would have a “better” result and then of course the “best” way is to field verify all three of these characteristics.

To offer some direction with this article I do believe that the most significant characteristic is the electrode configuration, followed by the enclosure dimensions and finally the conductor gap.

Again, just be sure to gather and model as much information as you can to achieve the most accurate results!

Hopefully this article finds you well and can be used as a reference for your project needs. If anyone would like to contribute to the Rochester Engineer and add an article or would like to requestinformation on a specific topic (not limited to Electrical) just email me at beliasz@bergmannpc.com. As always, any comments are appreciated…! Thank you for reading.

Brett Eliasz, P.E., LEED AP BD+C , RES Director