topic Circuit Length Question in Revit MEP Forum

Circuit Length Question

dtiemeyer — Wed, 01 Mar 2017 14:12:37 GMT

Is anybody using the Circuit Length (and therefore Voltage Drop) calcs performed by Revit?

If so, how do you compensate for the fact that the Circuit Length is measured explicity from connector to connector. We all know that conduits will run up/down out of a panel to the above/below the ceiling/floor then over to the connection point, and back across that ceiling/floor to the connection. This is almost always true (except when panels are immediately adjacent). How are you compensating for that distance. See the attached image if you dont understand my description. Thanks.

Re: Circuit Length Question

Anonymous — Wed, 01 Mar 2017 16:25:57 GMT

I never use the circuit length/voltage drop values from Revit, for that exact reason, but we don't generally accept responsibility for branch circuit wire size. We have a standard chart on our cover sheet with typical wire sizes for circuit lengths and make the contractor responsible for it - they're the ones laying out the conduit runs anyway. Anything >30A we'll probably specify the wire size with the caveat that the contractor is still responsible for verifying the voltage drop calculation.

Re: Circuit Length Question

dtiemeyer — Wed, 01 Mar 2017 16:34:04 GMT

Thanks for the feedback @Anonymous. We do the same thing for branch circuits (as wire size chart) but now I'm also looking at Feeder Sizing, which requires no greater than 2% voltage drop and it is something we want to be checking on every job, it would be a nice addition to the benefits of circuiting already provide.

Re: Circuit Length Question

Anonymous — Wed, 01 Mar 2017 16:38:51 GMT

Anything of that size I'll either just measure the distance or model the conduit and use that length to calculate the VD.

For service entrance feeders/large equipment you can probably trust the circuit length a bit further because those tend to be pretty straight-line installs.

You can adjust your VD criteria in Manage>MEP Settings>Electrical Settings>Wiring.