We also needed to model network circuits. At the time (June 11 release) the Circuit class/table that was already there looked to be for power circuits, based on the columns on the table. I now see in Berlin that it's actually listed in the Configuration application as Power Circuit, within Data Center. Don't know if Discovery might populate Power Circuit CIs, or if anything else assumes that they're power circuits. But we decided it was a bad idea to commandeer that class/table to mean network circuits, so create a new custom class/table.