Grounding @ Outdoor Panels

[LibertyEngineering]

Trying to determine grounding for a design where there is an outdoor panelboard fed from a panelboard in a building (equipment ground in the feeder included) and that panelboard feeds a sub panel also located outside (For a baseball dug out) At each of these outdoor panels, are you required to create a GES by driving a ground rod at each panelboard and therefore making sure the neutral and ground bars are not bonded in the outdoor panels?



In both cases the panels are 277/480 feeding a 15kVA step down transfomer. Are you permitted to share the ground rod driven for the 277/480V panel (if necessary per above question) for the grounding of the transformer and if so what determines the ground wire size connecting to the ground rod for the step down? The derived phase conductors or 250.66A?

 

[tortuga]

You generally need a grounding system at each structure served by a feeder. (250.32).
If panels are on the same structure you only need one GES.

what determines the ground wire size connecting to the ground rod for the step down? The derived phase conductors or 250.66A?

250.66(A) #6 copper to a ground rod.

 

[ptonsparky]

...rods...

 

[augie47]

agree with the above other than to say your GEC would be sized per 250.66 and could be as small as #8.( #6 is more common as a minimum due to 250.64 requirements._

 

[LibertyEngineering]

...rods...

Meaning each needs its own ground rod?

 

[wwhitney]

Meaning each needs its own ground rod?

Meaning one ground rod does not suffice as a GES. [Unless you go to the trouble of measuring ground resistance to be < 25 ohms, which is unlikely, and will take longer than just driving a second rod to form the GES.]

Cheers, Wayne

 

[LibertyEngineering]

You generally need a grounding system at each structure served by a feeder. (250.32).
If panels are on the same structure you only need one GES.


250.66(A) #6 copper to a ground rod.

Issue here is the first panel is out in the middle of a field there really is not a structure unless you consider the backboard it is mounted to.

 

[LibertyEngineering]

Meaning one ground rod does not suffice as a GES. [Unless you go to the trouble of measuring ground resistance to be < 25 ohms, which is unlikely, and will take longer than just driving a second rod to form the GES.]

Cheers, Wayne

ahhhhh yes of course forgot about that . Part 2 of my OP , Can the step down transfomer use the same ground rods?

 

[LarryFine]

Can the step down transfomer use the same ground rods?

Yes, one electrode system (e.g., two rods) can and should be used for grouped equipment.

 

[augie47]

Issue here is the first panel is out in the middle of a field there really is not a structure unless you consider the backboard it is mounted to.

IMO, the change in the definition of "Structure" in the 2017 Code would eliminate the need for a GEC at that panel.

 

[JoeStillman]

Meaning one ground rod does not suffice as a GES. [Unless you go to the trouble of measuring ground resistance to be < 25 ohms, which is unlikely, and will take longer than just driving a second rod to form the GES.]

Cheers, Wayne

This is in PA where 25 ohms is easy to get with one ground rod. No drought here - if anything, too much water.

 

[LibertyEngineering]

This is in PA where 25 ohms is easy to get with one ground rod. No drought here - if anything, too much water.

Amen to that my fellow Pennsylvanian

 

[LibertyEngineering]

IMO, the change in the definition of "Structure" in the 2017 Code would eliminate the need for a GEC at that panel.

Good point. I suppose its best to just add the ground rod and avoid the question from the inspector for the cost of it

 

[tortuga]

IMO, the change in the definition of "Structure" in the 2017 Code would eliminate the need for a GEC at that panel.

Good catch a post for a panel definitely in line with the def of equipment as its "in connection with" an electrical installation.

 

[ptonsparky]

Good catch a post for a panel definitely in line with the def of equipment as its "in connection with" an electrical installation.

Build something to hang it on and, your SOL.

 

[tortuga]

Build something to hang it on and, your SOL.

If I am understanding Augi correct, under the 2017 code and later, a 6X6 post sunk in the ground with some unistrut on it, to just support a panel, meets the NEC definition of equipment, as its "in connection with" "an electrical installation" and thus is not a structure.

 

[ptonsparky]

If I am understanding Augi correct, under the 2017 code and later, a 6X6 post sunk in the ground with some unistrut on it, to just support a panel, meets the NEC definition of equipment, as its "in connection with" "an electrical installation" and thus is not a structure.

Ok. I get it, but the rods went in any way.

 

[tortuga]

I have no doubt the first time I try that I will 100% get red tagged.