Volt Drop & Wire Size

[Admiral McAwesome]

Has anyone figured out a way to manually set the wire size in Revit 2011? I have found that Revit seems to be measuring from the fixture to the panel, and then back when calculating volt drop, so the wire sizes are usually incorrect when it comes time to upsize.

[RevitNinja]

The method of sizing is hard coded into the program. You can upsize by changing the circuit's rating parameter.

You can always add a custom project parameter to create a field for a manually added wire size.

[brad-TEC]

The distance is actually measured with parallel and perpendicular runs, from the furthest device, to each subsequent device, and finally to the panel. Fairly inaccurate, and not the way we (as I'm sure several others) do voltage dropping. When I posted a similar question last year, it was pretty unanimous across the board that no one used the wire sizes Revit was spitting out.

[Misteracad]

I saw a tutorial that noted the inaccuracy of wire lengths and sizing in Revit, and mentioned that there was an inherent flaw in the program. The suggested workaround was to DOUBLE the Max Voltage Drop values. The end result in the model should be lengths and sizes that more closely match what you would expect. However, calculating the true Voltage Drop would then have to be done manually.

Interestingly, I've yet to see anyone else identify the root of this problem, or offer a similar workaround. I can't help but wonder if Autodesk is going to get this fixed in an upcoming release. The info is not much good to you otherwise lol

[brad-TEC]

I saw a tutorial that noted the inaccuracy of wire lengths and sizing in Revit, and mentioned that there was an inherent flaw in the program. The suggested workaround was to DOUBLE the Max Voltage Drop values. The end result in the model should be lengths and sizes that more closely match what you would expect. However, calculating the true Voltage Drop would then have to be done manually.

Interestingly, I've yet to see anyone else identify the root of this problem, or offer a similar workaround. I can't help but wonder if Autodesk is going to get this fixed in an upcoming release. The info is not much good to you otherwise lol

When you say double the max voltage drop values, are you talking about the percentages? I could possibly see that making the sizes closer, but not the lengths. The way it determines the length is always going to be constant, and there really is no way (that I've found) to make them any closer to what we typically use (electrical center of the circuit). We have an in-house voltage drop calc which is very powerful, and I see us continuing to use it, even if Autodesk figures out a way to improve the built in functionality.

[Jimbob]

Hope I am reading this correctly but when we were going through training in 2010 I found (errors) problems in voltage drops and wire sizes, but actually they are right. I know in a lot of cases that the wire sizes shown in revit are something we would never design for or use but can be worked around by increasing the voltage drop settings to 10% instead of 3%. This will keep constant values throughout the project.

Go to manage > mep settings > wiring and see what your percentages are set for and increase by 10%