light pole mounted on precast plank

[malachi constant]

I am designing the installation of a 12'-tall aluminum light column mounted at grade. Normally "at grade" for me means you sink a bunch of concrete to structurally stabilize the pole and throw in a 10' ground rod tied to the pole base.

But in this case "at grade" is 12" of soil on top of an underground parking structure. After talking to structural I am bolting this straight to the precast concrete plank. Not sure how to ground it though. The main service is on the top level of parking about 100' feet away. Am I covered by running a #6 Cu back to the main grounding bar?

 

[rcarroll]

Your equipment grounding conductor supplied with your branch circuit conductors will ground the pole. What is the purpose of the 10' ground rod?

 

[haskindm]

If a pole is mounted on concrete that is in contact with the earth, how is installing a ground rod providing a better ground? I hope that you also specify that equipment grounding conductors be installed with the circuit conductors. If not, this is a disaster waiting to happen.

 

[tom baker]

A ground rod a at metal lighting pole is worthless. What you want is a bonding connection to the supply circuit to clear a line to pole fault. The concrete can take lighting hit without damage, I have a study done in 1970 that documents that.