Single Pot Transformer Neutral Requirements

[sparkyzman101]

I have three single phase 115 kva Delta/Wye transformers to hook up. Each transformer is one phase and has its own nuetral. These are service transfomers. Here are some specs:

-Delta primary 15800 volts
-Wye secondary 480/277 volts
-Secondary will be on a 3000 amp main

These transformers are in a vault and are also in a hospital under normal power. Currently the secondaries are two 1500 mcm wires per transformer on both the phase wire and nuetral and they run up to a buss duct. From there the buss duct leaves the transformer vault and goes into the Normal Distribution Panel. We have to eliminate this normal DP and install a more up to date version. We have to eliminate the buss duct and run cable tray in the transforer vault and into the back of the new DP. We have to run 8 sets of 500 mcm wire to each transformer per phase. Do we also have to run 8 sets of nuetrals to each transformers as well. Sorry about all the info. Just wanted to give a clear picture of the situation. Reusing the buss duct is currently out of the equation with having to do a splice in a tap box to make it work.

 

[11bgrunt]

Your question may not be clear to me.
Are you are using the three transformers to make a three phase service and the 277 is used to serve load? In a wye secondary, I preach the neutral should never be sized smaller than the hot legs. IMO you should run the 8 (sets?) conductors because of the single phase 277 loads.

 

[Smart $]

... We have to run 8 sets of 500 mcm wire to each transformer per phase. Do we also have to run 8 sets of nuetrals to each transformers as well. ...

You do have to run 8 sets to each transformer neutral bushing... but not necessarily all the way to the DP. You can run 8 sets between vault and DP, but in the vault you'll have to 'splice' three conductors to each main-run neutral conductor, running one of the three to each transformer neutral bushing.

The project engineer should check into bussing to connect the neutral bushings so you can just land 8 sets of neutral conductors and any required GEC's on the bussing.

 

[don_resqcapt19]

I have three single phase 115 kva Delta/Wye transformers to hook up.
-Delta primary 15800 volts
-Wye secondary 480/277 volts
-Secondary will be on a 3000 amp main
...

That looks like a lot less than 3000 amps available on the secondary to me. You have a 3 phase 345 kVA transformer, you need a 2500 kVA transformer for 3000 amps.