![]() ![]() But I'll also state that just about every Study I look at is flawed in some way. But of course bus diff is prevalent on systems above 1000 Volts because it's much more practical due to CT sizes.Ĭlick to expand.Not knowing all the details of the application, I'd say that equipment downstream of the circuit breaker would benefit from the characteristic curve device of the breaker, but only if it's in another cabinet. ZSI, maintenance settings and bus diff are also critical for IE reduction. In that case there was a section of the gear that was isolated and made inaccessible because the IE level was higher than 8 calories. That's just not possible in some cases if you have a coordinated system, but with enough money there are ways to get close. We did a large project for Harvard and their requirement was that 8 calories was the maximum incident energy (IE) level they would allow. But nowadays folks are adjusting breakers for arc flash reduction so now there's a whole lot of subjectivity to the adjustments. It's incumbent on the practitioner to exhaust every possible option for passing the equipment, which really comes down to NEC 240.86, series ratings.Īnother thing I like to say that is in days of old, when a Power Study consisted of Fault and Coordination, if your settings are implemented and there's a trip of a device and you're able to make adjustments that make things better, then you screwed up with your original settings. In fact the thing I see that is most flawed in Power Studies is where equipment fails the equipment evaluation exercise because the button was pressed and it said it failed. ![]() ![]() There's so much misinformation out there, and anyone can buy a Power Systems analysis package, enter the data, and press the button for arc flash calcs, or for equipment short-circuit evaluation. ![]()
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