GEC for SDS

[barclayd]

We are installing a 75kva 480/208Y120 transformer 300' from the Service Entrance Switchgear.
250.30(A)(3) Exception #2 allows the Grounding Electrode Conductor of a service to also be used for a Separately Derived System.
Normally we would run 3#2, 1#6G, and provide a Grounding Electrode at the transformer.
Using the above exception, would we run 3#2 phases, 1#6 EGC, plus 1#2 GEC?
Do we, somehow, need to identify the GEC differently from the EGC?
Do we even need the EGC if we promise not to cut/splice the GEC?
We'll probably do it the old way, but thought I'd see if anybody has done it this way.

 

[A/A Fuel GTX]

would we run 3#2 phases, 1#6 EGC, plus 1#2 GEC?

The GEC would only have to be a #8cu per 250.66

Do we, somehow, need to identify the GEC differently from the EGC?

IMO...yes

Do we even need the EGC if we promise not to cut/splice the GEC?

IMO....yes

Is there any building steel close to the transformer you could use to land the GEC to?

 

[infinity]

Maybe you could explain your setup a little better. Are you talking about running the GEC in with the feeder to the primary of the transformer?

 

[augie47]

We are installing a 75kva 480/208Y120 transformer 300' from the Service Entrance Switchgear.
250.30(A)(3) Exception #2 allows the Grounding Electrode Conductor of a service to also be used for a Separately Derived System.
.

I belive those two sentances clash. 250.30(A)(3) begins by stating: Exception No. 2: Where a separately derived system originates in listed equipment suitable as service equipment,
If your transformer is 300 ft from your service equioment, your SDS doesn't originate in the service equipment.

It has alwas been my understanding that this exception is for an assembled service switfhboard that has a SDS as part of the assembly.

I don't think in this case that exception is applicable.

 

[wirenut1980]

In my opinion the exception you cited does not apply to the installation you described. I believe the exception is describing a situation where there is one piece of equipment containing the service, as well as a separately derived system, that is listed for that purpose.

Plus I think the installation you described would be pretty confusing and if it were allowed I probably would not recommend doing it that way.

My vote is for the old way. Call me old-fashioned.

 

[wirenut1980]

augie, you beat me to it, and you added blue coloring to your wording. man, you're good!

 

[augie47]

he still uses crayons...

he still uses crayons...

you ought to see my inspection reports,,, for someone who still uses crayons, I do o.k.

 

[barclayd]

I believe the exception is describing a situation where there is one piece of equipment containing the service, as well as a separately derived system, that is listed for that purpose.

OK - I guess, based on the definition in 100, the Separately Derived System would start at the transformer secondary. The Feeders and the primary would not be part of it.

I remember some old Bulldog panels that had 480v on top and 280 on the bottom via an internal transformer. Don't remember how the transformer was grounded.

thanks
db