An arc flash study involves digging deep into the electrical power system and can uncover design issues and deficiencies such as inadequate interrupting ratings, incorrectly sized overcurrent protection and more.
So, this week’s question….

Has an arc flash study ever uncovered design issues/deficiencies?
Yes
No
Not involved with studies

Let’s hear about the craziest design issues you have seen/heard about being found during an arc flash study.

There will not be a Question next week, as the U.S. celebrates its Independence Day holiday!

Yes. Many.

The most common deficiency I come across is on large 208V services or feeders with available fault current greater than 10K that has a branch panel very close to the main switchboard or panelboard and a very short feeder length resulting in greater than 10K available at the panel and the panel has 10KAIC rated breakers.

I see that a lot. Many times I can find and/or create a series rating to solve it but sometimes I've had to change the breakers out to -VH's etc., 22K.

I've also found many instances of where adjustable trip breakers were shipped from the factory with minimum settings and nobody ever attempted to do a coordination study and/or set the breakers or if they had nuisance trips the breakers were arbitrarily maxed on all available settings to make sure it didn't happen again.

To solve the overduty / under rated issues I start with looking at the existing OCP devices and see if by chance a series rating exists. If it doesn't then I see if I can change out the feeder breaker or fuses to get a series rating, failing that I try to add a fuse ahead of the panel to get a series rating failing that I look at changing out the panel or breakers in the panel or possibly adding feeder conductor length if it is feasible and less costly than equipment change out.

I've also changed out very low impedance three single phase oil filled "can" type transformers (1.6% Z) to a new 3 phase pad mounted transformer (6% Z) to lower fault current to below the equipment rating. The single phase cans and the equipment were both very old to start with and it was much faster and cheaper to change out the transformers than the main switchboard.

Mostly, we see underrated panel boards, meaning A.I.C. violations. We see the opposite where someone has over done it. For example, the use of low peak fuses where there is no need for that level of fuse. Low peak fuses cost quite a bit more.

We do see maintenance failures or mistakes. Bolt lock switches that have never been maintained and won't open. We've seen 480 bus duct with cutting oil dripping out of all the disconnects. Or how about thick layers of fiber (not sure exactly what the fiber was) everywhere including inside most of the panels, motors and controls. Then the home made gutters with too few insulators for the support of the 480 bus. The same gutter with large openings so someone could easily contact the bus. How about the use of plumbing pipe instead of EMT or GRC conduit. This install included the use of plumbing elbows. How did they got the wire thru the elbows?

The worst was a NEMA 1 120/208 volt load center installed outdoors. It gets better, the load center was put on the side of a very hot furnace. This 120 volt rated panel had 480 volts on it. Almost all the wire used was white and because they'd run out of breaker space, they simply loosened the main lugs and put #10 and #12 wire under the lugs.

Naturally, once in a while we see copper pipe instead of fuses, or splices of wire inside conduit, and even worse, the use of the metal conduit as the neutral conductor. That use of the conduit can be particularly scary. One of us was trouble shooting a problem on a roof. He saw a conduit had come apart so he figured he'd re-connect it. He (bare handed) touched both ends of the pipe. He became the neutral wire of the circuit. He was okay, but wow, you want to go after the meathead that did that.

We almost always find something that is needs to be repaired or tested. We find many code violations and equipment where the settings are set on the factory shipped minimum settings. I tell our customers that performing an Arc Flash Study on an existing facility is like a QC check of their electrical system. It is a great way to reduce the owner's liability exposure and to increase the overall electrical system reliability.

I've found many arc flash studies are very incomplete or have incorrect data, often throwing the values off significantly. Oh you meant the equipment itself...one of the biggest problems is AIC and short circuit on cables. Thats on top of poor maintenance and installation practices. One of the most common is failure to install plastic bushings on conduit penetrations. Always finding either impending or already happened faults there.

We have found:
CTs not connected to relays.
Operation circuits mis-wired for CB control.
Aftermarket sensors on LVP circuit breakers that were tapped or sized incorrectly.
Copper pipe used in place of fuses.
Numerous ways of getting the wrong fuse to fit in a fuse holder, including using piles of zip ties.
1940's era MV transfer switch (missed for replacement after a factory recall).