separately derived system

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Ragin Cajun

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Upstate S.C.
I have an existing concrete framed building, no building steel, and I need to add a new 480-120/208V transformer.
Just where do I connect the grounding electrode? The nearest thing that's "grounded" is the transformer feeder conduit. Running a bare conductor down 5 stories seems pointless.

1673397031801.png

What do you do?

Thanks,

RC
 
Are there other transformers in the building ?
If so, there may be a common electrode system {250.30(A)(6)} that you can connect to
 
I guess my problem boils down to: How to "bond", or whatever, the neutral of a transformer located on the upper floors or roof of a building with no structural steel or a water line at the upper levels???

This can't be the first time this comes up!

In the picture everything AVAILABLE IS TIED TOGETHER.

Thanks!

RC
 
Note, all I have to go on is the photo they sent me.

All the green wires are interconnected
One originates at the 3000A 480V switch gear feeding the transformer.
The other go to the new 120/208V panelboard.
Apparently since they could not find any building steel, etc. the grounding electrode conductor, conduit, etc. were not run shown in the detail below. I don't know what more that can be done.


1673469907391.png
 
Then a GEC must be run to the nearest or easiest qualifying point.

Can the supplying pathway have such a conductor added?
 
Side question: What size are you transformer secondary conductors and grounding conductors ??

If you follow 250.121 you might use the primary equipment ground as your GEC.
 
FWIW: Assuming the #8 "G" is the SSBJ, a #8 is undersized; with a 2/0 it should be a #4
 
Typo on the drawing. But since I can use the conduit as the EGC, It should be ok.

Actually with a 150A MCB, 1/0 is good.

Still leaves me with separately derived systems on the upper floor/roofs of a concrete building and the GEC. Looks like 250.121 is the ace in the hole here.

Thanks
 
Ragin Cajun said:
Typo on the drawing. But since I can use the conduit as the EGC, It should be ok.

Still leaves me with separately derived systems on the upper floor/roofs of a concrete building and the GEC. Looks like 250.121 is the ace in the hole here.
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The conduit may be the EGC, but it cannot be used as the GEC. You must have a conductor.
 
Looking at you drawing it say run one. However your evoking 250.121
So size the EGC/ GEC correctly.
#8 will not be code compliant.
You say 1/0 on secondary assuming CU. 250.66
says #6 on the primary side EGC/GEC. The same for SSBJ.
Watch for 250.64 E on the primary side
 
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