Straight runs of cable tray in Revit are a system family and cannot be modified, which is a problem because Revit doesn't create cable tray correctly in accordance with industry standards. The industry standard for cable tray width is the inside dimension between the side rails which gives you the width of the available space in the cable tray for you to run your cables in. The way Revit draws the tray is outside to outside dimension.

Here are references to cable tray width from ABB, Eaton, Code Electric, and Unitray for example:




This is a problem since unless you explicitly know that Revit errors in this way you will be placing tray that is too small into the model. This may throw off required code clearances when it comes to construction, and where things like wall and floor penetrations are incorrectly sized for the true size of the cable tray.
This also creates issues with detailing sheets. If you use Annotation Tags for cable tray and you have oversized the tray in the model to match the real world tray size it will not give you a correct width in your tag. The workaround solution that we have come up with works for the fitting families. A parameter can be created with a formula to offset the width value, but this doesn't work for system families.
if(Tray Width > 955 mm, 0 mm, if(and(Tray Width > 952 mm, Tray Width < 955 mm), 914 mm, if(and(Tray Width > 799 mm, Tray Width < 801 mm), 762 mm, if(and(Tray Width > 647 mm, Tray Width < 649 mm), 609 mm, if(and(Tray Width > 494 mm, Tray Width < 496 mm), 457 mm, if(and(Tray Width > 342 mm, Tray Width < 344 mm), 305 mm, if(and(Tray Width > 190 mm, Tray Width < 192 mm), 152 mm, 0 mm)))))))
For instance if I need a 12" cable tray and I put a 13.5" cable tray in the model to account for the error, when I put an Annotation Tag on that tray it will say width is 13.5".