Is it possible to have a circuit feed both a lighting panel and a rooftop RTU? I have a set of 4/0's protected at 200amp from an MDP that is split in a j-box, the 4/0's continue to feed a lighting panel and a set of 3/0's goes up to a rooftop RTU. I don't have all the details of the rtu disco, fusing etc, but assuming they were all rated properly, is this installation possible? Is this considered a tap?

It's not a 'tap' unless some of the conductors are rated less than the OCP protecting them.

It is sure a unusual set up but it could be code compliant if the load, conductors and overcurrent protection all match up properly.

Yeah--

Unfortunately, that's what I think too. But maybe forcing a detailed load calculation of the panel will convince them to do a separate run to the RTU. Sure hate to have to shut down lighting in half the place in order to work on the unit.

Thanks.