Using steel wire mesh as ground
Using steel wire mesh as ground
(OP)
Hi There,
First let me state I am a Structural Engineer so not up date on the electrical requirements for grounding. We have a warehouse building that is being built on slab on grade which has steel mesh through out the slab. The mesh comes in 5'x10' segments and is tied together with galvanised wire. Is it possible to use this element instead of running a 4/0 ground wire around the perimeter of the slab (The electrical engineer specified this). The mesh has a steel area of 252mm2 per meter each direction.
First let me state I am a Structural Engineer so not up date on the electrical requirements for grounding. We have a warehouse building that is being built on slab on grade which has steel mesh through out the slab. The mesh comes in 5'x10' segments and is tied together with galvanised wire. Is it possible to use this element instead of running a 4/0 ground wire around the perimeter of the slab (The electrical engineer specified this). The mesh has a steel area of 252mm2 per meter each direction.






RE: Using steel wire mesh as ground
Reinforced below-grade concrete footings are a good ground and in fact, the NEC requires a connection to these in addition to a ground rod or other "made" electrode. Google "Ufer ground".
For a typical warehouse, I'd expect a ground rod, a ufer ground to a footing steel, if available, and the useless water pipe ground connection. The perimeter copper is not a bad idea, but not typically done for a warehouse that has modest power requirements.
Cheers,
Dave
RE: Using steel wire mesh as ground
RE: Using steel wire mesh as ground
"Not in this case. NEC also does not apply.
We have to have ground per the transformer section to ensure equipotential bonding and no possibility of electrocuting anyone. What you do not understand is that we have both North American AND European breakers in this building. This building employs both North American Neutral breakers and European real ground ELCBs.
The resistance to Earth must be lower than an Ufer method to avoid electrouciton because the breaker will not trip when there is a fualt in the other system, - it simply wont detect the fault because the ground floats in North America."
This still confuses me as I thought all we needed to do was use enough concrete encased reinforced steel to produce a low enough impedance to match that of the 4/0 copper cable. as I have 7000 SF of heavy mesh in this slab I thought that would do it.
RE: Using steel wire mesh as ground
RE: Using steel wire mesh as ground
1)continuos 4/) copper wire placed in the slab just inside the perimeter of the building(125' x 150ft) so the cable is about 350ft long.
2)"Bond reinforcing steel @ 4points(2 each bay).Using #4/0 exthermic bonding method.
3) Extend 18" ground pig tail for future connection(3 locations as shown)
So each of the 3 pigtails are shown next to 3 column located at the ends and center of the building.
I am assuming the 4 connections are connected to the foundation steel in 4 quadrants of the building plan to distribute the grounding evenly.
As there is no ground rod system then this appears to me to be a Ufer system. However as I have one foundation with 14 5/8" bar that run continuous top and bottom and it is 125ft long couldn't I just connect the pig tails to that and make sure the rebar is bonded properly. Would this save a lot of money on copper cable? The client is very cost conscious.
RE: Using steel wire mesh as ground
This sounds confused - or perhaps I'm confused. Sounds like he is describing two separate electrical systems, one of which is ungrounded. Seems like a complex system for a "warehouse". Most systems in the US are solidly grounded.
Where is your EE from? And where is the project?
Again, rebar in concrete is a fairly good ground as long as the concrete is below grade and stays moist. Copper in the slab is fine, but not strictly a Ufer ground.
RE: Using steel wire mesh as ground
WIKI is your friend;
https://en.wikipedia.org/wiki/Ufer_ground
You may want to diplomatically share this with your EE.
Bill
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"Why not the best?"
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