Service Transformer Secondary GEC, GEC, SSBJ Confusion

[arc_flashed]

I am hoping someone can help clarify the requirements for grounding an electrical service. I've come across an install that needs a secondary customer owned transformer to step down the voltage from the utility transformer and I am having a hard time getting my ground sizes and terminology together.

The utility transformer has a secondary voltage of 480/277vac. Customer needs 120/208 so a step down transformer will be installed. This transformer doesn't need a neutral on the primary, so I haven't planned on pulling one from the utility, but supply side bonding jumper should still be pulled correct? This would be connected to the utility transformer ground, no the X0?
Then my step down transformer will have both a SSBJ and a neutral conductor with the bonding occurring in the first means of disconnect.

I've attached a drawing of my system and what I believe the correct grounding and terminology is but I do not have a lot of experience with new services.
Any help is greatly appreciated.

 

[infinity]

Although it can be sized the same as the SSBJ a neutral is required from the utility XFMR to the service disconnect.

 

[zooby]

Although it can be sized the same as the SSBJ a neutral is required from the utility XFMR to the service disconnect.

picturing this.....is the conductor landed at either end ? or its just "taped off" ? Thanks...

 

[augie47]

Someone else may catch something I didn't but I see no real "sizing" problem.
A few comments:
Terminology: As infinity notes.. the grounded conductor to the service would actually be considered a grounded/neutral conductor not a SSBJ but you have it sized correctly (a SSSBJ is not needed on utility services)
The GECs to a ground rod don't need to sized larger than #6
The 600 amp distribution does not need to be service rated. But, since you are doing your bonding there, no problem

 

[jim dungar]

picturing this.....is the conductor landed at either end ? or its just "taped off" ? Thanks...

It is landed just like it is in any other service equipment. Effectively at X0 in the transformer and the neutral bar in the service location. Of course the neutral would need to be bonded to ground, so an actual neutral bar may not be needed. Typically you need to have a method for isolating the neutral and the grounding conductors, but this is part of the requirements for UL listed Service Equipment.

 

[arc_flashed]

Someone else may catch something I didn't but I see no real "sizing" problem.

For sizing, I was referring to using the correct table to get the required cable size. If I had incorrectly identified the type of ground (GEC, EGC, SSBJ, etc) I may have gotten the size wrong by using the incorrect table.

A few comments
Terminology: As infinity notes.. the grounded conductor to the service would actually be considered a grounded/neutral conductor not a SSBJ but you have it sized correctly (a SSSBJ is not needed on utility services)

If the grounded conductor would be considered a neutral, is it still sized per 250.102?
This install will likely use underground conduit (PVC). The ground for this feed/conduit will be covered by the neutral?

Not to complicate the original question, but if my transformer had been 3P3W, would I pull a SSBJ?

The GECs to a ground rod don't need to sized larger than #6
The 600 amp distribution does not need to be service rated. But, since you are doing your bonding there, no problem

 

[don_resqcapt19]

For sizing, I was referring to using the correct table to get the required cable size. If I had incorrectly identified the type of ground (GEC, EGC, SSBJ, etc) I may have gotten the size wrong by using the incorrect table.

If the grounded conductor would be considered a neutral, is it still sized per 250.102?
This install will likely use underground conduit (PVC). The ground for this feed/conduit will be covered by the neutral?

Not to complicate the original question, but if my transformer had been 3P3W, would I pull a SSBJ?

Customer owned transformers always need a supply side bonding jumper. The fact that it is an ungrounded system does not change this. The only thing that is different between the bonding and grounding of an ungrounded separately derived system as compared to a ground SDS is that the ungrounded system does not have a system bonding jumper. Everything else is the same.

 

[augie47]

Not to complicate the original question, but if my transformer had been 3P3W, would I pull a SSBJ?

As don says, yes on a customer owner SDS.. on utility I honestly don't know. (I was in hope don would know).
All the 3p3w services I have encountered were overhead with no SSBJ. Unsure on a pad transformer.

 

[jaggedben]

Where is the service point?
(First things first...)

 

[don_resqcapt19]

Not to complicate the original question, but if my transformer had been 3P3W, would I pull a SSBJ?

As don says, yes on a customer owner SDS.. on utility I honestly don't know. (I was in hope don would know).
All the 3p3w services I have encountered were overhead with no SSBJ. Unsure on a pad transformer.

If it is a service, there is no SSBJ. The utility will have connected the transformer case to their grounding electrodes, and a grounding electrode system would be installed at the service equipment.