Distribution to many MCC'S - Transition Box?

[designer82]

We have a large Electrical Room that will house 12 MCC'S rated 480V-3PH

There will be a Switchgear Substation just outside not far from this Electrical Room.

The design problem we're having is that running all the feeders in underground ductbanks from the Switchgear Substation to the Electrical Room is prohibitive ampacity wise (calculated in ETAP - significant derating requires 7 sets 750kcmil to each MCC... too much)

Running many cable trays is possible but it's MANY cable trays. 1 for each MCC would be 12 total 30" wide cable trays.

What about running 1 or 2 large cable trays or cable busses with enough power to feed all 12 MCC'S then using a large transition box inside the Electrical Room to tap from to each individual MCC from there? Is this practical?

What is your experience with a situation like this and the typical design approach?

Thanks

 

[petersonra]

My first thought is the tap conductors to each MCC would need to be 1/3 the ampacity of the upstream OCPD rating.

 

[augie47]

You might give some thought to 70E. Without individual protection ahead of each MCC you could not isolate the individual MCC to perform maintenance, etc.

 

[drktmplr12]

what voltages do you have available at the substation?

medium voltage from the substation to MCC
padmount xfmr to 480v
busduct into MCC

 

[JEFF MILLAR]

Good question. More details please. Physical layout, What is the bus rating of the MCC, Can you attach your one line.
Duct banks are great but the derated ampacity and limited number of ducts is a killer. I can help if you can supply the details.