Waste water Tank Grounding

[Paul McNichol]

I am working on a project at a Waste Water Treatment Plant. The project involves the installation of three in ground concrete waste water tanks (open to the atmosphere). The tanks are relatively close to one another 25' minimum 40' maximum separation). The tanks are connected via underground cast iron piping. Each tank has an electrical control panel associated with it which is fed from a distribution panel in close proximity to the tanks. The distribution panel is fed from the plant distribution system. The control panels serve pumps or blowers for the tanks plus some controls. The panels are interconnected via underground PVC conduit. We are putting in ground rods at each tank connected via an underground bare copper ground loop around the tanks and we are bonding the ground loop to the rebar, grating and metal structures associated with each tank. We are unsure as to whether we should connect the ground loops to the distribution panel or rely on the ground conductor routed with the feeder to each control panel? Any thoughts?

 

[raider1]

Welcome to the forum.

These ground rods, ground ring and concrete encased electrodes would be auxillary grounding electrodes and you would connect them to the equipment grounding conductor supplied with the feeder to the control panels.

Take a look at 250.54.

Chris

 

[tom baker]

We are putting in ground rods at each tank connected via an underground bare copper ground loop around the tanks and we are bonding the ground loop to the rebar, grating and metal structures associated with each tank.

Is this for lightning protection?
If it was at a service then it would be part of the Grounding electrode system.
And it would of been far better, and far less cost to use the reinforcing steel in the tanks to creat a "ufer" ground.

Anyway it would be considered a auxilary ground. But I would bond as a grounding electrode if lightning was a consideration....

Big difference is in sizing of GEC and protection -see 25.64E

Also there is a NFPA standard for WWTP electrical and fire- 820, have you looked at it?

 

[QES]

Yes, bond the ground loops to the distribution panel.
Also, remember to bond any exsiting grounding grid/loop to your new grounding system.