I am interested in hearing how other electrical engineers and firms do their voltage dropping, mainly for circuits with multiple fixtures (ie, lighting runs). The reason I ask is because the way we do it seems to be completely different than the way Revit does it...
The way we have done it for years is to use the "electrical center" of a circuit, and then run parallel and/or perpendicular to walls all the way back to the panelboard. So, for instance, if you have a run of lights that are the same, and equally spaced, then the "electrical center" of the circuit will be in the middle of the run. If you have a circuit with different loads spaced sporatically around the area, then it is obviously harder to find the exact center. On a project I am currently working on, I had determined that the electrical center of the circuit was ~75' from the panelboard.
Now, from what I can gather (since I don't think its actually spelled out anywhere), Revit uses the entire length of the circuit for voltage drop. I built a schedule to return values similar to our in-house voltage drop spreadsheet, and found that Revit returned a value of 175'.
This now caused the circuit to go from #12 wire to #8 wire. When I plugged the same values into our in-house spreadsheet, I found that with #10 wire, the resulting voltage drop was 3.02% (I had it specified in Revit for 3%). So for us, we feel the built in wire sizing in Revit is invalid and not usable, which sucks. So my question is, is anyone else under the same opinion? Or have you even checked it against the way you were doing it before Revit?