Using same conduit for feeder and emergency power back to main panel

kwmivp

Main Panel /Meter is at the house, and the Shop/Garage 50 feet away. The power to the shop is provided via 3 wire AWG6 with 60amp breakers at both ends, The conduit to shop is 1 inch Sch40. In a power outage the Inverter (AIMS 12KW with 60amp breaker) would provide power, supported by an 18kw Generac (6kw to charge banks, remaining to feed house). I want to run a separate set of wires in the same conduit from the inverter back to the main panel to a 60amp breaker (with interlock to street main breaker).  Can it share the conduit? Can I leverage the existing Neutral (AWG6) from the house to the sub, and just run 2 new live wires back to the house from the inverter?

Dave Angelini

On the edge here for safety in 1 ".  (6) conductors allowed in PVC, Is there a ground?  Sharing neutral is the path to bad results.
 Ask your building department and get it in writing. Why people use 1" conduit is beyond me,  but 50 feet is not far to do it right.

 Another way to look at it is if you have home insurance or if it ever would be inspected? 
If you sold the place you would have to disclose this.