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Old 07-24-2012, 10:37 AM   #1
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grounding a detached pipe frame building in rocky ground


I have a pipe frame "cabin" that i have installed a sub panel in...cabin is 500sq ft and pipe is set in 8 places...2-3ft in ground...in concrete...ground is too rocky to put rods in ground ( we had a hydraulic drill put in holes for pipe), i am trying to figure out if i need to run separate ground from sub panel and where/how to do it...ive been told "ok to ground to pipe frame" and also " do not ground to pipe frame"...have also read about a "grounding plate"...i have a 2ft length of 4" I Beam....would burying that 18-24" make a grounding plate?

Any help is appreciated...please no "drive a rod"...the area is almost solid limestone...it took power company over an hour to drill for their service lines and there truck was huge...thx


Last edited by rmcmallen; 07-24-2012 at 10:38 AM. Reason: problem with quotation marks
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Old 07-24-2012, 11:05 AM   #2
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grounding a detached pipe frame building in rocky ground


You need to be more clear on your question and your description of the cabin.
Is this is a sub panel or a service panel?
It is not connected to any other structure?
Does the cabin reside by itself with no structure supplying the power?

If this cabin is supplied with power from another structure it requires a ground rod/rods and an ECG (ground wire) from the supply source/structure.
You might be able to use structural members in this case as the grounding electrode. Only your local inspector can allow or disallow this. Have you asked the local inspector?

What does (rod&quot) mean? Where are you located?

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Old 07-24-2012, 11:44 AM   #3
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grounding a detached pipe frame building in rocky ground


sorry....the cabin is a stand alone building that is wired as a sub panel (the main panel is near the barn, approx 150 ft away). the wiring is 6ga (3 individual strands running about 250 ft of line from main panel), 70amp breaker at main panel....the sub panel is 125amp box with main breaker....

as i mentioned, unfortunately, driving a rod into the almost solid limestone is really not an option....i'd be lucky to dig 18-24 inches deep at best....i've been told i could ground to the actual pipe frame of building but i've also been told i can't ground that way...

the ground plate sounded like a possibility, but i won't be able to bury it much more than 18-24 inches at best....i was wondering if a 2 ft piece of 4 inch I beam would work (i read where the surface area of the grounding plate is the key)

anyway, i hope this gives you a better idea
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Old 07-24-2012, 12:59 PM   #4
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grounding a detached pipe frame building in rocky ground


You need to connect all the structural steel to the grounding system. That's important anyways. Whether the steel can count as the grounding electrode or not is a different issue. It probably cannot, according to code. You would technically require two ground rods or another approved grounding electrode. However, from a practical perspective, there's really no point. The steel structure will be a better grounding electrode by far than a couple of rods, and you might as well just use it.
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Old 07-24-2012, 03:41 PM   #5
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grounding a detached pipe frame building in rocky ground


Under some conditions (I'm not sure of the details) you can bury the two ground rods horizontally if you can't drive them vertically.

The metal structure needs to be bonded to the ground rods (using the #6 copper grounding electrode conductor) anyway and if it is a better ground then you are better off although the two rods satisfy the National Electric Code.
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