Calculating SCCR Short Circuit Current Rating and Tips for Raising

[@_DigitalCam]

Current limiting breakers are a great way to help your SCCR. Another interesting way to go about it if your working the SCCR from more than just the panel components, isolation transformers can reduce the available fault current to the panel so that the panel might only have to be built to tolerate 25kA instead of 35 or 65kA. It’s important to note for the folks who are new to SCCR, the number you’re achieving and labeling your panel with isn’t a “warm fuzzy number” like “I think I’ll just build this one to 65kA.” The engineer at the plant or install site needs to be able to identify the available fault current to the panel. If they can’t, you’re going in blind and you’ll essentially be guessing! SCCR can be a deep dive! Not too bad once you get some practice with the principles and what not.

[@TimWilborne]

Adding the transformer would make for a good video.

[@santhoshreddy4793]

yes, i am interested in learning more information on current limiting CBs, please

[@TimWilborne]

Noted! I'm working on the details

[@TheDrewbe3]

Tim, these are interesting topics that I do not see many people discuss. In your experience, how often do people specify panels to be UL508A? Or even care or specify what the SCCR rating needs to be for panels being designed & supplied. I understand the importance, especially when it comes to the interrupt devices being able to interrupt the maximum available fault current that the power system is capable of supplying. Also, the fact that the performance of the interrupt devices plays a role in determining the incident energy that is calculated in arc flash studies. However, in my experience things like this seem to get little attention up-front on projects, or even completely missed altogether. I work in the steel industry, which may play a role in why.

[@TimWilborne]

I see UL and SCCR requirement on most specifications I see these days SCCR isn't something new. It has been required by NEC since 2005 and UL 508A since 2006 so it is nearly 2 decades old. I would say it is getting rarer to see a panel without a SCCR rating but also just as rare that it actually be correct :) UL 508A...if you work in the steel industry then I'm sure you are no stranger to OSHA. They require all control panels be certified by a Nationally Recognized Testing Laboratory (NRTL). There are 21 to choose from but UL is the largest. I think what is making more panel manufacturers pay attention now is many companies are no longer just requiring a UL sticker and SCCR rating, they are starting to require a certain KA rating on the panel which is a real hard mark to hit if you don't think about it up front.

[@robertgriffith3475]

Perfect timing for me. Great explanation. What are the benefits of raising the sccr of a cabinet? It seems a typical controls cabinet will almost always come out to 10ka or lower, correct?

[@TimWilborne]

Great question and probably worthy of a follow up video. The big two reasons are it reduces the danger to a worker inside a live cabinet and lowers the risk of a fire.

[@jeremyschmitz395]

how would the wire have a better sccr rating than a copper bus bar to connect the fuse together ?

[@TimWilborne]

The wire is not part of the SCCR equation.

[@traviscoleman9520]

Hey Tim. Have you possibly thought about doing a series on Autocad electrical drawings? Specifically a controls project from beginning to end would be awesome. The stuff on Udemy and other platforms out there is not great.

[@TimWilborne]

I have thought about it but I'm pretty dated on my drawing methods. Fellow KZbinr Kai Hennings does a good job on Eplan. Check him out. www.youtube.com/@eplaninanutshell

[@santhoshreddy4793]

Tim, Thank you for this gem. However, in your schematic, you are using 3 pole CB for Single phase 120v + N. If you do so, shouldn't you feed L from TERM2 into TERM 3 and move N into TERM5?

[@TimWilborne]

No, not according to installation instructions. Do you have a reference? The only mention was the neutral conductor protection but we weren't in the criteria to need that.

[@santhoshreddy4793]

@@TimWilborne@TimWilborne, you see the wiring reference in the wiring details for a motor protector. I have a system I am working with, and the schematic calls for ABB MS132-10T are on the primary side. However, only 2 (575VAC) lines are used in this case. I called ABB and explained the situation. They informed me that we cannot leave any terminals on the CBs; for example, if two-phase lines are used, you can feed phase 1 to L1 and draw from T1. but for phase 2 - feed into L2 then loop T2 to L3 and then draw from T3. Similarly, if you use the same motor protector for a single phase with neutral on the secondary size (230VAC), you must feed the line through the CB twice and neutral through the 3rd pair. I know this is the most wacky wiring I have ever seen. Since the toggle and MP CBs work almost on the same principle, shouldn't the wiring be the same, too?

[@TimWilborne]

Ah, that sounds like a motor protector with phase loss protection. Not the same as a circuit breaker...just to make it extra confusing, it isn't necessary to do the loop through a motor protector if it doesn't have phase loss protection.

[@santhoshreddy4793]

@TimWilborne Thanks, Tim. That helps a lot. I promise this is the last question - The guy also said I can use it for a single phase with a neutral. Since there is a phase loss protection, I cannot pass neutral through it right? Please advise

[@TimWilborne]

I'm not familiar enough with the ABB device to say one way or the other.

[@jackpast]

Tim, is this rating used when calculating total calories for arc fault protection?

[@TimWilborne]

Yes, it is part of the equation

[@thelegendwarrior7896]

@TimWilborne how to connect security camera on panelview 7 plus ?

[@TimWilborne]

I'm pretty sure it's possible but honestly I don't work the Panelview Plus much

[@aaqilkhan]

Your video title is confusing - why would you want lower SCCR rating? The SCCR indicates the maximum short-circuit current that a component or assembly can safely withstand. A lower rating is bad and you would ideally want want higher, which means better safety and reliability for your electrical circuit.

[@TimWilborne]

Typo, corrected...thanks!