davidbeach, I agree concerning the realistic accuracy of system models, both utility and industrial. Sometimes I feel I am doing surgery in the dark with the arc-flash analysis. But at least the hazard is being addressed.
I think I've gotten a fairly good sampling of the community's feelings...
From experience as a former utility engineer, the utility provides this information as a service, not as design information. NFPA 70E recommends updating a facility's arc-flash study every five years (if I'm wrong, correct me) ,if no major changes have occurred on the facility system, in order...
I actually haven't had too difficult of a time getting realistic fault currents from utilities. I've done arc-flash analysis for companies across the U.S. and had pretty good cooperating with most utilities, once they understood why I needed an accurate value. Usually you just need to talk to...
I don't care about equipment withstand here. I'm conducting an arc-flash hazard analysis. I've already determined in another part of this study that the equipment is suitable for an infinite source bolted fault. Where did I mention equipment fault withstand?
In IEEE 1584 Section 5.2, an...
Does anyone else have a problem with the IEEE 1584 incident energy equations for current limiting fuses?
Incident energy is based on the arcing fault current, not the bolted fault current. Arcing fault current is determined from the bolted fault calculation but takes several other variables...
Good point, jraef! I hadn't thought about that. Assuming an infinite primary bus, a 50kVA dry-type with approx. 5.0%Z, only about 1200A can be delivered to a bolted 3-phase fault.
Still, I have no control over the source of the 480V; customer may decide to feed from a separate 480V utility...
I've been asked to evaluate a panel for SCCR labeling. The panel is fed from a 575V source. The 575V source feeds some 600V equipment, leaves the panel to an external 50kVA 575/480V transformer, then the 480V circuit comes back into the same panel and feeds 480V equipment.
So, how do I label...
I actually had this problem in a motor protection application. The 50G would pick up during starting, but there would be no 50N (core balance CT) current. The DC component of the phases would not balance in the calculation, but no return current was present, I assume because the generator...
That's what I'm inclined to do here. My arc-flash numbers will be quite conservative as there will be only two phases contributing to the fault, correct?
Anyone have suggestions for conducting an arc-flash study on a 480V, three-wire, grounded-b system? Is this possible? If so, should it be treated as an ungrounded-delta? Not sure where to start with this one... TIA!
