Hey everyone,

Hope you are all enjoying the holidays. I am posting to this forum to talk about some of the challenges I have come across since I began performing power systems studies about 4 years ago and hopefully learn some solutions based off of your responses. To put things into perspective, I work for a small consulting engineering firm and our company mostly works on building electrical design. I am hired out by contractors, manufacturers, and distributors to complete power systems studies for mostly low voltage applications (120/208V or 277/480V systems). Our contracts include short circuit analysis, equipment evaluations, protective device coordination analysis and arc flash hazard risk assessment with labels. Again, I am posting here to share some of the challenges I have seen when trying to complete these studies and I have listed them below. Please let me know how any of you have dealt with these issues when completing your studies and how you have dealt with them.

1) Withstand and Close on Ratings are constantly failing for the Automatic transfer switches on my projects. The Withstand and Close on Ratings are normally dependent on the upstream overcurrent protective device. Transfer switch manufacturers normally provide a list of specific breakers and their correlating Withstand and Close on Ratings, but I usually don't get any information on what type of transfer switches are being used until the end of my projects when the equipment is already on site. This then leads to the awkward conversation of telling the manufacturer and the engineer that they need to switch out their breakers to provide proper ratings for transfer switches. Please let me know how any of you have dealt with this.

2) Achieving full selective coordination on emergency branches has become more and more difficult recently due to either bad design by the engineer or due to cheaper molded case circuit breakers with fixed curves being used by the manufacturer. It would be awesome if everyone used fuses on their emergency equipment, but this seldom happens with the projects I work on. I normally try to spot any issues with coordination early on in the project and notify the engineer or manufacturer, but sometimes I don't have all the information I need right away to build the study and the engineer and manufacturer often times release panels and equipment before receiving the study. Once the study is finally released, I am stuck with telling the engineer and manufacturer that they don't have full selective coordination and that they need to switch out breakers to achieve proper coordination. Please let me know how any of you have dealt with this issue.

3) I keep running into issues where I never have enough information from the contractor / manufacturer to provide a fully complete study. Usually I provide a preliminary study that tells the engineer and manufacturer what the proper ratings of their equipment should be. My issue is that towards the end of my projects when I send out a final study that includes arc flash hazard risk assessments, I am kind of in limbo waiting for the manufacturer, engineer, and contractor to finalize everything on their end. I know that I can make assumptions on some things, but it just drives me crazy because I never quite have all the information that I need. For those of you that do these studies, do you just make assumptions and then provide the statements in your studies? Here's an example of an issue that I'm dealing with: I have a study with emergency systems and the contractor has not provided any information about the generator breaker or automatic transfer switches and I can't really make assumptions on this equipment if I'm providing an arc flash risk assessment or ratings for that matter. I don't want to hold up the entire study, but the contractors are impossible to get any information out of sometimes. Let me know what you all think.

Best Regards,
Engineer in Training


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Basically someone needs to more pre planning and that is the bottom line. We have the same issue here when our own in-house firm drops stuff off at the door and it is wrong from the start (multi national, multi billion dollar corporation). In a world where everyone in contracting out or Value Engineering, we end up with an incomplete deficient project that is supposed to last 30+ years. All I can say is keep to the facts and keep pushing for planning. You may not like the conversations and will feel pressure to capitulate but stick to your guns. Stick to engineering and good project management practices. I am running a large study for our plant now and see this every day. We are in the middle of 600,000,000.00 dollar expansion and equipment upgrade. The pressures are intense and are felt every day. Everything from a small air handler unit to a new utility substation installation and everything in-between. Wait until you get to deal the workmanship issues. Dont let others " lack of Planning or poor planning " make an emergency on your part. PLAN PLAN PLAN and thn Plan some more.

From the sound of it you are gaining solid experience with ATS and emergency system coordination. Why not leverage this experience to provide your clients a Specification or detailed list of these issues, something like "ATS's are required to meet XYZ minimums for Withstand and Close on Demand ratings" and "For a selectively coordinated Emergency system, provide XYZ circuit breakers in upstream-downstream combinations of A, B, & C". I guess what I'm advocating is rather than wait for others to limit you, why not provide a list of requirements/best practices for them to meet? And then when they don't your firm has a case for additional services fees. At my firm we like to state all of our assumptions right up front in our Design Basis or Scope of Work documentation, that way 1) the client knows what they are getting and 2) we are building a case for when others (GC, other firms, etc) cause re-work in our design. So add DOCUMENT DOCUMENT DOCUMENT to PLAN PLAN PLAN.

In regards to your Item 3 concern, I would run the AF study without the generator breaker and see if the results are higher than with the Utility. If not I would just provide labels a the higher results. In reality, if a facility is running on emergency power the chances on someone signing off on hot work is slim to none.

This is pretty typical. If I ask the manufacturer to supply specs on MCC breakers (main breaker or MCP's), I get nowhere quickly. With generators you get the same "deer in headlights" look in terms of the primary breaker on the generator. Generator manufacturers tend to be of two varieties. You either get the engine manufacturer such as Caterpillar who is private labelling both the generator and the switchgear, or you get a generator manufacturer that private labels the engine and the switchgear. Rarely someone will contract the switchgear and the generator/engine separately which means that it can be in the bid spec and you can control this somewhat. Otherwise the best time to get information is when the equipment arrives on site and to recognize that generatlly speaking either the breaker or the transfer switch or both are just about throwaways.

At our firm, we specify the upstream devices (both generator and switchboard) as well as the automatic transfer switches, and we list the required withstand rating for the ATS's on the drawings. Our basis of design ATS and switchboard breaker will meet the withstand rating. When we review shop drawings, we typically hold back returning the ones for ATS, generator, and switchboards until we have received all of them, so we can verify ATS withstand rating.

If during the shop drawing review we determine the ATS will not have the required withstand rating, we put the onus on the Contractor to change either the ATS or the upstream device(s). That is because when the Contractor deviates from the basis of design (typically to save money), it becomes the Contractor's responsibility to address any problems this causes.