When to install ground rods for utility pad mount transformer?

[choppedslaw]

I’m installing utility pad-mount transformer underground.

Relevant details:

•Spec calls for (2) ¾” x 10’ copper-clad ground rods.

• Note states: “Install two 3/4” x 10’ copper weld ground rods driven to a minimum depth of 9’-0”.”
• There is a copper ground bus mounted in the transformer pad window (at finished grade elevation).
• The rods connect to that ground bus inside the window.

Current site condition:

• Excavation is approximately 4’ deep below finished grade.
• Pad/window elevation is at finished grade.
• Primary and secondary conduits are already installed and and stubbed up from the excavation.

My question is about sequencing and driving elevation:

If I drive the rod from the bottom of the 4’ excavation:

• Driving 9’ would leave 1’ exposed at the ditch bottom.
• That would put the rod top 3’ below the pad window.
• I would not be able to reach the ground bus.

If I drive only 6’ from the ditch bottom so the rod top lands at grade, I would only have 6’ embedment, which does not meet the 9’ minimum driven requirement.

So it seems the only way to both:

1. Achieve ≥9’ embedment, and
2. Have the rod top land at the pad window for connection

Is to backfill/bring the area up to near grade and then drive the 10’ rod from that elevation.

Is that the correct interpretation of “driven to a minimum depth of 9’-0”” in this context?

For those who do utility pad-mount work regularly:

• Do you typically drive rods from finished grade elevation once the pad base is built up?
• Or is there another accepted method in this scenario?
• I’m concerned if I backfill then drive rods I run the risk of hitting the installed underground conduits. Primary side is robroy sweeps. Secondary side are pvs 90s.

I want to make sure I meet embedment requirements while also keeping the rod top accessible for connection to the ground bus in the pad window.

Appreciate any insight from those familiar with utility primary installations.

 

[don_resqcapt19]

How are the rods to be connected to the bus in the transformer?

 

[choppedslaw]

How are the rods to be connected to the bus in the transformer?

Ldn-050n

 

[hbiss]

Excavation is approximately 4’ deep below finished grade.

Drive the rods 4' into the bottom of the excavation. Backfill then set the transformer. That's what I have always seen.

-Hal

 

[don_resqcapt19]

Ldn-050n

no idea what that may be

 

[qcroanoke]

no idea what that may be

Ground bar to wire connector.

 

[don_resqcapt19]

Ground bar to wire connector.

so there is wire between the ground rod and the transformer...if so, I would install the rods as deep as possible and extend the wire up to the transformer.