Ground rod installation in concrete slab

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skeshesh

Senior Member
Location
Los Angeles, Ca
Hello everyone, hope all is well.

As a young engineer there are many times I feel I'm lacking in the practical side of things, and here's yet another one: What is the typical method of driving a ground rod into earth through a concrete slab inside a building? What tools are usually used to accomplish this?
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
What is the typical method of driving a ground rod into earth through a concrete slab inside a building? What tools are usually used to accomplish this?
Use a rotary hammer (not a hammer-drill) with, say, a 3/4" percussion bit to make the hole, then a rod driver bit in the same tool to drive the rod. Note that you may need a longer-than-8' rod to qualify, technically speaking, unless you bury the clamp.


And, yes, all is well, thank you for asking. :)
 

roger

Moderator
Staff member
Location
Fl
Occupation
Electrician
I agree with Larry, do a search for Rotary hammers to see different manufacturers versions.

Roger
 

skeshesh

Senior Member
Location
Los Angeles, Ca
Thanks for the quick response guys. Yea, I've specified a 10' rod and included references to NEC 250.52(A)(5) and 250.53(G) as well as 250.10 for protection of the clamp/connector (plus we always toss the ground spec in for all jobs just in case so this stuff's all been included in the bid documents). It's just that someone in our office asked if they can drive it and how hard it would be to do - I told him I'm sure it's pretty easy since it's done ALL the time, but it's a bit embaressing to admit that I have no idea how it's actually installed! Luckily there's this forum and its experienced contributors so I knew where to go to get a quick answer.
 

iwire

Moderator
Staff member
Location
Massachusetts
It could be hard if you are asking for a 10' rod and have less than about 14' of height above the location.

I had a to install a 20' two section rod and ended up drilling a hole in the next deck above to do it.
 

M_J_C

Member
It could be hard if you are asking for a 10' rod and have less than about 14' of height above the location.

I had a to install a 20' two section rod and ended up drilling a hole in the next deck above to do it.
I've run into the ceiling height situation before, the best solution I've found is using sectional copperbonded ground rods from Erico. You can get them in 3,4,5,6,8, and 10' lengths, just use their threaded couplers and continue to drive the assembly down until you achieve the engineering spec. (depth and/or impedance) for the job.

http://www.erico.com/products/copperbonded.asp
 

M_J_C

Member
Post Tension slabs can be a problem too from what I understand.
Only if you consider a steel cable shooting out of the side of the slab at near super-sonic speeds a problem!

Worked a number of PT building slabs in the 80's. None of them were on the ground floor. If anyone needed to drill or chip the slab, we would have to get the onsite engineers permission for each location. I can't remember how much tension those cables are under but I remember vividly what happens when they fail. They would either blast a hole in the slab that you could fit through, or shoot out of the end of the slab about 20 feet or so.

When the iron workers would apply tension to the cables after the concrete had cured enough, everyone was kicked of off that floor and the floor below for the duration, for safety reasons.

Made you think hard about putting that bit to the concrete.
 

iwire

Moderator
Staff member
Location
Massachusetts
I've run into the ceiling height situation before, the best solution I've found is using sectional copperbonded ground rods from Erico. You can get them in 3,4,5,6,8, and 10' lengths, just use their threaded couplers and continue to drive the assembly down until you achieve the engineering spec. (depth and/or impedance) for the job.

http://www.erico.com/products/copperbonded.asp
It was a two piece 20' rod, I mentioned that. :)The ceiling height was about 9' so screwing the second one onto the first required a hole in the second floor deck.
 

skeshesh

Senior Member
Location
Los Angeles, Ca
The building does not have any structural steel and the engineer who originally designed the project did not check with the architect/structural eng. Application is a data room and the grounding + groundbus is required per clients standards and TIA.

I specified sectional rod, I don't think the ceiling height is more than 12' but I havent measured it. I think it's managable though; the RFI I received from the contractor did suggest using a ground rod and the architect doesn't have a problem with that. I also contacted the engineer in charge of the client's communication/IT maint. and he also OKed it.

Thanks much for all the input.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Made you think hard about putting that bit to the concrete.
I doubt any concrete one would want to drive a rod through (read: has earth under it) in a building needing one or more (read: is existing, no rebar/Ufer connection available) is going to have tensioning in it.
 

wasasparky

Senior Member
I know this is aside from the point, but I'm not sure there is any added value in installing a ground rod through an interior slab.

I guess I would be more concerned about having a good ground grid and bonding all systems coming in or out of the computer room.

And I hope the IT folks don't want to isolate the computer ground from the service ground...
 

skeshesh

Senior Member
Location
Los Angeles, Ca
I know this is aside from the point, but I'm not sure there is any added value in installing a ground rod through an interior slab.

I guess I would be more concerned about having a good ground grid and bonding all systems coming in or out of the computer room.

And I hope the IT folks don't want to isolate the computer ground from the service ground...
To be honest I dont understand the reason either. The IT/comm manager for the client told me its per some TIA standards (TIA 607A?) but I haven't had time to look into it (4 deadlines this month, 1 big project coming, 4 under const., 1 about to get into conts.) but I will asap. The application as I mentioned is a data room which has dissipative tiles and copper bus bars on walls for easy grounding of the server rack, etc. bodies. The only reason i can think of off the top of my head is that another ground path at that point will decrease the impedance of the ground system at that point and will create less noise.

I have done isolated ground for other clients where they use an isolated testing chamber. In those applications we isolate grounding from the room, provide a chemically grounded well + rpd which provides isolated ground in the room and provide RF filters for each current carrying conductor entering the room. Chamber room mfg. have their own standards of sealing the room penetrations etc. and I got the details from them and tossed them on the drawings.

I would like to continue this discussion to find out why its necessary to provide another ground connection to struct. steel, cold water pipe, ground rod, etc. for this case. It'd be much appreciated if there was other input, else I'll post under this topic again once I review the TIA standards that the client's comm rep referred to.
 
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