That's what I thought at first; a real available fault current calculation is not necessarily straightforward, so I started asking questions about what point in the system they wanted the calculation done for and what the conductors were, etc., but then my client showed me one that passed. AFC at the transformer plus AFC at the inverter(s). OK, that's easy, but I don't see the significance of the result.
Why should they remain nameless? If you recall a week or so ago I had a thread on a inspection failed by Seattle sdci. Obviously I named the ahj, I did not name the inspectors involved, but I would have if my appeal had been unsuccessful. Why hide the information?
Since inverters shut off under fault conditions when the voltage is out of spec, is this really any different than the fault current calculation for a service and distribution system in general? Even if you account for the maximum possible current, it's still small enough that it is barely even a rounding error, in most cases.
All capacitors are ignored when performing fault current calculations.
I know that caps store very little energy, but it can be discharged very quickly. Ever run any numbers on what the contribution of a large PFC bank would be?
Apparently ggunn has a greater concern about retribution than you do.
Retribution would be an illogical response. If a member of the involved AHJ did happen to view the thread, they would also see no support for their position and logically they should question and re-evaluate their position.
I dont think any software, like Etap or SKM, considers any capacitor contribution at all, even if I wanted it to. Motors have a decaying magnetic field which can contribute some fault current.
Because I already have a bit of a contentious relationship with the AHJ in question and I do not want to exacerbate it. I could go on, but I won't.
Yeah but are AHJs necessarily logical?
In a meeting a couple of years ago, a rep of an AHJ took the opportunity to bring up a disagreement we had over another completely unrelated issue that had occurred a couple of years before. Before I could stop myself I told him he had been wrong then and was still wrong. The meeting did not go well after that.
How does "shoe" taste??
I apologized profusely to the other members of my company's delegation to that meeting when it was over, but to a man they all told me that they wished they had said it.
While inverters would shut down this functionality is not considered a protection function under the arc fault calculations. So the calculations are done assuming that an inverter is able to output its fault current indefinitely into a fault and it would only be interrupted by a fuse or CB in the circuit path.
In the arc fault calcs, the output of the inverter is modeled based on a multiple of the rated output and that's it. The internal capacitors and inductors are not evaluated as adders. But their existence is part of the reason the fault current from an inverter is 1.2-1.3X the rated output.
The 2021 NFPA 70E has a new annex R that covers capacitors and electrical safety issues. It covers the arc flash hazards of capacitor banks and SKM can use capacitor banks as a source in the arc flash calcs. It's a newer area though so the application is still inconsistent.
