Over the years, I have heard a few stories about how an arc flash study was put on hold due to discovering deficiencies such as code violations, inadequate short circuit interrupting ratings etc.

The hold was until the deficiencies were resolved.

The reason cited was usually liability i.e. finding the deficiencies (or having deficiencies found), and now knowing about it and what could happen if it remained unresolved.

So, this week’s question:
Have you ever halted an arc flash study or had a study halted due to deficiencies that were found?

Yes
No
Does not apply

I have started methodical study throughout an entire site. 6.5 miles of busway,1500 bus plugs and approximately 7000 pcs of equipment.
I have stopped due to major issues but have since kept moving and developed a plan. I document all deficiency's found and shops are looking and scheduling repairs.
SCCR is a complete subject onto itself. I am addressing new equipment only or rebuilding old equipment as major upgrades are being proposed.
I surely hope we could include some more SCCR questions in this forum as this goes hand in hand with Incident energy. I have finally(4 years) started to gain some traction with correcting installations at our plant. I sure could use the support and offer some as well.

Stopping work is kind of like a rite of passage for maintenance...there shouldn't be very many people out there that have not been in a situation where it becomes obvious that you need to stop right where you are at, reassess the situation, and take a much different approach before proceeding.

As to SCCR...there are quite often some surprises here. Be careful of WHICH short circuit estimation method you use. They are all designed originally back when we did all the calculations by hand, usually with a slide rule. IEEE/ANSI Std. 141 for instance is the most common in the U.S. and IEC 60909 is common elsewhere.

One example of a "short cut" method is to first calculate transformer short circuit current assuming an infinite bus on the primary side. Use a fixed impedance for inductive loads (motors, transformers), and ignore cable impedances altogether.. Depending on the method used these approaches sometimes (but not always) do look at transient conditions in the first few cycles since the goal is just to check AIC conditions (make sure that busbars don't fly apart and that circuit breakers will actually open under instantaneous tripping) This will result in a short circuit calculation which is quite often much higher than it would ever be in reality. However since it is relatively inexpensive to oversize everything in terms of AIC, this is what was commonly done in the past.

Although it's not quite that bad, ANSI/IEEE Standard 141 is pretty close to this extreme, and IEC 60909 isn't far behind. Here is an article that discusses some comparisons of the various methods in a little more detail which some real world charts showing just how far off the calculations can be:
http://www.cired.net/publications/cired ... _paper.pdf

When it comes to incident energy of course the focus is just the opposite...low short circuit current is quite a bit more problematic than high short circuit current because it will significantly increase trip times, which with most circuit breakers and fuses tends to increase incident energy. So all the above estimating short cuts which resulted in a high short circuit current also result in excessively low incident energy estimates.

So my experience has been that although a lot of equipment might be flagged especially using the IEEE/ANSI Standard 141 method, further and more detailed short circuit studies which are typically available in most power system analysis software with just a few clicks quite often shows that it's not as bad as it looks at first and that many "dangerous" situations are not as bad as they seem at first. That's not to say that if nobody is looking that SCCR doesn't matter...far from it. Just that it is usually not as bad as it looks in many cases.

You can usually tell this for a given plant, too. Take a look at past incidents and look at how many of them showed characteristic over-dutied failures...circuit breakers that never tripped, bus bars ripped and bent apart, etc. If you're not seeing signs every time a short circuit fault happens, then the estimation may be overly conservative. If you are, then obviously some work needs to be done.

I generally would not stop my work for an equipment deficiency. I generally would not even know about it until I have collected all the data and start running studies. I would provide data/labels for downstream devices. I would clearly note the deficiency and warn that correcting the issue may nullify any or all of the existing study.

Once I have notified the owner of any deficiency does not mean they will replace the equipment and the down stream equipment would have the current ratings. Hopefully the owner takes responsibility and corrects the issue or, at the very least, let the qualified electrician know of the issue.

Only one that I can remember.

Coal fired boiler house. All of the equipment filled with coal dust. Coal dust in the air. Wire insulation very brittle looking and much of it 50+ years old. Almost nothing explosion proof. After opening a dozen or so fusible switches in a live main switchboard and seeing the condition I did not feel comfortable opening any more live equipment under the circumstances.

It was tough to read the fuses due to so much coal dust without sticking my hands in to wipe it off and forget about the printing on the wire insulation. I didn't research what category coal dust is to be sure but I felt like I didn't need to.

I recommended postponing the study until equipment could be shut down and cleaned. Tough to do since the plant provides steam to a hospital.

For equipment deficiencies, we would include those deficiencies in our arc flash study. They need to know what equipment is not safe to work on, or maybe even to operate at all.

As for stopping an arc flash study, the two deficiencies that will force me to stop are usually with the configuration management of the facility (e.g. drawings or lack thereof), and maintenance. I have refused to provide arc flash calcs for facilitates where the maintenance was abysmal.

You'd halt a study due to lack of drawings?

A lot of studies would be halted if I did that. One of the several goals of the study is to give the Owner an accurate as-built one-line when the study is complete is it not? The only way to do that right is by field surveying, not assuming what is on a drawing is accurate.

If you're looking at all the gear, OCP's, cable and raceways as part of the survey how could you not produce your own drawing by default? When I do a study I only use the drawings as an aid to help me locate equipment and as a fallback on a cable size if I can't tell when surveying. It is very common to come across discrepancies between the available drawings and what was actually installed.

If I believe the drawings are pretty good to start with (newer facility) I may go ahead and build the model based off the drawings but I then take that model with me when I survey and still verify wire sizes, raceway types and routes and all OCP's. It can make the survey portion go faster if I'm just checking off 90% of the stuff I already had from the drawing rather than building it from scratch but I'd never halt a survey because I didn't have any drawings. I'd create my own.

I do not delay studies even for obsolete equipment. The only factor that delays for me is getting utility information. I investigate the condition of the equipment while collecting field data, perform thorough analysis and inform the customer of risk associated with the equipment. I put the photos of the equipment in the report and provide recommendations for mitigation.