Gentleman, I have an installation where, due to some monumental blunder, wires designed to be overhead in conduit are now to be run in a concrete trench. These are feeding power to various devices using 12-250kcmil (qty 4 of 3-wires) and qty 2 4-wire of 2/0.
I understand that concrete...
Interestingly I just found the rated voltage stamped on the transformer: 6.92%. That makes an actual SCC of 69kAIC.
I can understand a small overstatement, but this is ridiculous. Do you think providing actual values of the transformer and reduced SCC to an Advisory Committee would be a...
Luckily we have some long conductor lengths that will take care of about half the needed impedance. I roughly calculate the reactor to be 4.7mOhms.
Voltage drop at rated current is 1.5% with the above sized reactor and conductor impedance. Not too bad.
The CLR is basically a big...
Thanks for your help David. Looks like a current-limiting reactor is going to be the best/simplest/easiest solution.
There are hundreds of CB's that are either already existing or being installed by too many subcontractors to try to coordinate some kind of current-limiting fuse at the meter...
I see where I'm missing something: current-time curves are only applicable to low-level and over-current faults. For high-level faults (a.k.a. short-circuit) the energy let-through and total clearing time needs to be considered.
Thanks for your responses, and sorry for any vagueness.
DPC, I think you are right about the transformer; I did not realize distribution-sized transformers can have %Z as low as 2.3. That is right in line with the impedance and AIC the utility gave.
Let me make sure I understand CLF's in...
An installed transformer vault has 4 1000kVA transformers 13.8kV - 480V. The utility rates this installation at 200kAIC and (145, j1385) uOhms. There are a couple of issues I am having with this.
1) Why don't the Utility ratings and the xfrm ratings match? Assuming 5% impedance on the...
