Grounding @ Outdoor Panels

Status
Not open for further replies.
Sparky2791

Sparky2791

Senior Member
Location
Northeast, PA
Occupation
Electrical Design
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?
 
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.
LibertyEngineering said:
what determines the ground wire size connecting to the ground rod for the step down? The derived phase conductors or 250.66A?
Click to expand...

250.66(A) #6 copper to a ground rod.
 
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._
 
tortuga said:
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.
Click to expand...
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.
 
wwhitney said:
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
Click to expand...


ahhhhh yes of course forgot about that . Part 2 of my OP , Can the step down transfomer use the same ground rods?
 
LibertyEngineering said:
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.
Click to expand...
IMO, the change in the definition of "Structure" in the 2017 Code would eliminate the need for a GEC at that panel.
 
wwhitney said:
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
Click to expand...
This is in PA where 25 ohms is easy to get with one ground rod. No drought here - if anything, too much water.
 
augie47 said:
IMO, the change in the definition of "Structure" in the 2017 Code would eliminate the need for a GEC at that panel.
Click to expand...
Good catch a post for a panel definitely in line with the def of equipment as its "in connection with" an electrical installation.
 
ptonsparky said:
Build something to hang it on and, your SOL.
Click to expand...
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.
 
Status
Not open for further replies.
Top