Ground rod for SDS transformer...yes or no

[meternerd]

We are installing a three phase Wye Wye step down transformer (480/277 to 208/120), fed from a 480/277 breaker panel. We have a ground rod, UFER and water piping bonds installed for the building 3P4W grounded main service. Do we need to drive another ground rod for the neutral of the step down transformer or can we just connect to the grounding electrodes of the main service? The transformer will feed a three phase 208/120 breaker panel. The high and low side neutrals will not be connected to each other. I assume this makes it a SDS. All equipment is in the same building.

Do I need to run the 480V neutral to the transformer primary neutral if all the breaker feeds is the transformer?

 

[augie47]

The transformer secondary will need a grounding electrode as specified in 250.30(A)(7).
You do not want to connected the neutral to the transformer on the primary side.

 

[GoldDigger]

The transformer secondary will need a grounding electrode as specified in 250.30(A)(7).
You do not want to connected the neutral to the transformer on the primary side.

And all EGC wiring on the secondary side must connect to the common point of the secondary grounded conductor (if there is one) and earth ground, not to any non-separately-derived-system EGC that is lying around.

 

[templdl]

It's interesting why wye-wye transformers are being used. These are common in the utility industry but not in the industrial commercial industry unless there is a unique application requirement.

 

[tom baker]

Yes you must install a GE system and SBJ. 250.30 has a specific list of GEs to use, just go down the list and use what you have. If the main building GES is close to the SDS then you will likely end up using it.

 

[SparkyHC]

The transformer secondary will need a grounding electrode as specified in 250.30(A)(7).
You do not want to connected the neutral to the transformer on the primary side.

Yes, as Augie says, do not connect the transformer neutral on the primary side...
many years ago we did and the result was a room full of smoke and a missing ground wire...