Utility Transformer feeding power distribution box, feeding three transformers. Are ground rods needed at each transformer

[Greenautomator]

This is for an EV site, a utility transformer is feeding a 2000 amp discount.
Main bond jumper installed here tied to 2 ground rods.
The 2000 amp disconnect feeds 8 450A disconnects.
Each feed to a 480V 400A fused disconnect.
Each 400A fused disconnect feeds a 167KVA transformer 480V single phase primary to 240/120V single phase secondary.
Each Transformer feeds 2 120/240 branch 400A branch panels, each having 4 2 pole 100A breakers for EV chargers.
EV's together are limited to 320A

Question is if each of these transformers need its own ground rod?

 

[Elect117]

They require a grounding electrode. Whether it is two rods or the system's electrode like building steel or water pipe is based on the types present. See 250.50. The short answer is two rods at each transformer, 6' apart and 8ft deep. Or tie all of them into a single grounding electrode bus/conductor. See 250.30(A)(6). I guess that kind of depends on the layout.

Don't forget protection is based on both 450.3 and 240.21(C). You will need a low side OCPD for the conductors coming off the transformer rated at the conductor ampacity. A MCB in each 400A board and parallel runs of 3/0 will do that. Taps are not permitted on the secondary side of the transformer before the first OCPD. So each set feeding the down stream boards must originate at the transformer's point of connection.

 

[jaggedben]

If the transformers are considered to be at separate structures (e.g. they are pad mounted and spread around a grade level parking lot) then each would have its own electrode(s). See 250 32. If all the equipment is in the same building or structure (e.g. different stories of a built parking garage) then they are all supposed to be connected to the *same* grounding electrode(s.)

IOW all the transformers require a connection to the grounding electrode system at their respective building or structure.

 

[Elect117]

If the transformers are considered to be at separate structures (e.g. they are pad mounted and spread around a grade level parking lot) then each would have its own electrode(s). See 250 32. If all the equipment is in the same building or structure (e.g. different stories of a built parking garage) then they are all supposed to be connected to the *same* grounding electrode(s.)

IOW all the transformers require a connection to the grounding electrode system at their respective building or structure.

I was under the impression you could do either if it was outdoors. As in, create a single bus grounding electrode conductor near the main and run the transformer's electrode conductors to that along with the service main.

And if it was easier, than drive the rods at the transformers.


** Edit - reading it back, it sounds like you are elaborating.

 

[jaggedben]

I was under the impression you could do either if it was outdoors. As in, create a single bus grounding electrode conductor near the main and run the transformer's electrode conductors to that along with the service main.

And if it was easier, than drive the rods at the transformers.


** Edit - reading it back, it sounds like you are elaborating.

Yes, I don't disagree. Note I said if the transformers are 'considered' to be (or be at/on/in) separate structures. If you have a group of pad mounted transformers on the ground outside the code definitions give no clear guidance on how close to or far away from each other they have to be in order to be considered the same or different structures. So within reason I'd say you can make the call either way.