Increasing a service and generator - adding an ATS to an existing

[jkassebaum]

I am working on an upgrade to a waste water treatment plant. The new equipment will require increased service from 400A to 800A (480/277 3ph 4W). There is currently a service entrance rated 400A Automatic Transfer Switch and a 150kW generator along with a 150KVA transformer for existing service. All of the power is brought into the existing ATS cabinet which has a lower gutter area for a pull box (cabinet 72" tall, bottom space is approx 27" tall, 32" wide, and 22in deep - there are four 3" conduit entries in the floor of the cabinet from below grade). Current wiring is 500 kcmil from the transformer and 2 x 3/0 from the generator. There is an additional spare conduit for both the generator and the transformer wiring that could accommodate new 500 kcmil and new 500kcmil or 2 x 3/0 for a new generator. I want to pull the new wiring into the old ATS cabinet and set a NEW service entrance rated 400A transfer switch net to the old ATS. Then, I would pull the new wiring to the new ATS beside the old one, thereby having tow 400A main service breakers in side-by-side ATSs to power the facility. Am I allowed - per the code - to pull the new additional wires originating from the transformer and generator from the old ATS cabinet to the new one next to it? I am in Indiana FWIW - 2008 NEC. Thanks for any feedback!

 

[tortuga]

Am I allowed - per the code - to pull the new additional wires originating from the transformer and generator from the old ATS cabinet to the new one next to it? I am in Indiana FWIW - 2008 NEC. Thanks for any feedback!

As long as the generator conductors and the service conductors stay in their own raceways (NEC 230.6) your good to go.

(cabinet 72" tall, bottom space is approx 27" tall, 32" wide, and 22in deep - there are four 3" conduit entries in the floor of the cabinet from below grade).

Sounds like someone sized the pull box for future expansion.

There is an additional spare conduit for both the generator and the transformer wiring that could accommodate new 500 kcmil and new 500kcmil or 2 x 3/0 for a new generator.

 

[jkassebaum]

As long as the generator conductors and the service conductors stay in their own raceways (NEC 230.6) your good to go.

Sounds like someone sized the pull box for future expansion.

Thanks! Yes - the feeders from the generator and the service conductors from the Utility transformer enter the building from under grade at the old ATS-1 in separate conduits. In addition, there are two spare empty conduits of the same size entering the ATS-1 from under grade - one from the location of the generator and another from the location of the utility transformer. Once in the ATS-1 they are connected to the normal and emergency sides of the transfer switch. I am planning to place an identical service entrance rated ATS (ATS-2) beside the older one and pull the NEW service conductors and generator feeds via the spare conduits in the bottom of ATS-1 into the bottom of ATS-2 and connect its normal and emergency sides. I am virtually certain is allowed, but I appreciate your corroboration! Many Thanks!