Ground rod at seperate building

[jap]

What is the point of driving a ground rod at a seperate building when a Ground wire is already pulled with the feeder to it?

 

[pete m.]

The "ground wire" is the intended ground fault current return path and the "ground rod" is for lightning.

Pete

 

[iMuse97]

Isn't that the same as any time a ground rod is driven? There's always a wired pathway, but if it is required by code, it is required. Places I work require redundant and/or additional grounds, not code specs. but client specified.

And yes, as Pete says, the Ground Rod is generally called a secondary ground. The wired ground to the main panel in another building is the primary ground. So it's about safety, redundancy.

 

[pete m.]

Isn't that the same as any time a ground rod is driven? There's always a wired pathway, but if it is required by code, it is required. Places I work require redundant and/or additional grounds, not code specs. but client specified.

The OP might be referencing the change in the 2008 NEC in 250.32(B) that now requires the equipment grounding conductor be routed with the feeder (exception noted). In prior editions of the NEC we were given a choice to bring the EGC or not dependent upon the existence of any other electrically conductive paths between the structures that would/could be bonded at both ends.

Pete

 

[jaylectricity]

What is the point of driving a ground rod at a seperate building when a Ground wire is already pulled with the feeder to it?

If the building gets struck by lightning do you really want that charge to flow through the feeder all the way back to the main service when it really doesn't need to?

 

[jap]

I would tend to think that an undetermined amount would anyway.

 

[jaylectricity]

Right, but you're trying to minimize the damage. Some gets to ground through that first ground rod, then some gets to ground through the one by the main service, then maybe some back into the POCO's grounded conductor, leaving very little to look for the water ground.

 

[jap]

Is a ground rod required at every seperate building regardless of wether it is a feeder or Branch circuit brought to it?

 

[raider1]

Is a ground rod required at every seperate building regardless of wether it is a feeder or Branch circuit brought to it?

No, the exception to 250.32(A) permits you to not install a grounding electrode if the building or structure is fed by a single branch circuit. For the purpose of that exception a multiwire branch circuit is considered to be a single branch circuit.

Chris

 

[jap]

and why is that?

what changes?

 

[raider1]

and why is that?

what changes?

JMHO but if the structure or building is only being supplied with a single branch circuit the building or structure would probably be small enough that a close lightning event would not induce very much current in the buildings wiring system.

Chris

 

[jap]

Thats a good point.
I wonder if most lightning damage comes from an actual surge on the ungrounded conductors induced by a strike to the HV lines rather than an actual direct hit where it travels down the ungrounded path?

 

[jap]

sorry,

Grounded path.

 

[massfd]

If you were installing a 50a RV (4 wire feeder) recept on a post would a ground rod be required.