Deep Rod Earth Grounding
Deep Rod Earth Grounding
(OP)
I would like to propose some discussion to those smarter than I. I have been asked to evaluate the possibility of installing deep rod earth grounding around a new facility. Here are the details: New building 50k sq.ft. for a satellite uplink facility. The building was installed with a ring of 10' rods, 20' spacing, and a #2/0 ground loop. The resistance is several hundred ohms since the soil is quite sandy. The contractor tells me they practically pushed the rods in, as the soil was so loose. There is an old existing well, but it's resistance was poor as well; about 600ohms at 100'. I do not have soil data yet, but I wanted to ask people experience and success rate with installing deep rods at the corners of buildings, etc. No body wants to deal with chemical rods at this point.






RE: Deep Rod Earth Grounding
Perform a soil resistivity test and on the basis of that model your earth, then you know the dept at which your earth rods can penetrate.
There are some soil enhancing material that you can purchase and treat the imediate surronding of your earth rods with. These have a great effect in reducing the soil impedance.
RE: Deep Rod Earth Grounding
shttp://www.erico.com/newsDetail.asp?newsid=64ite conditions.
RE: Deep Rod Earth Grounding
I almost feel how dry the soil is down to 30 feet. You add lenth after length and it doesn't get any better. Then, you hit water table! And here we go again!
Done that. Seen that. You really have to go deep for a low earth resistance. The deeper the lower
Gunnar Englund
www.gke.org
RE: Deep Rod Earth Grounding
RE: Deep Rod Earth Grounding
RE: Deep Rod Earth Grounding
RE: Deep Rod Earth Grounding
RE: Deep Rod Earth Grounding
In areas such as Minnesota, 30-foot ground rods are common in substations.
RE: Deep Rod Earth Grounding
Why does the cleint think this is necessary?
RE: Deep Rod Earth Grounding
RE: Deep Rod Earth Grounding
One problem with ground rods is the small surface area of the typical 1/2" (50 mm) diameter rod. A 3.5 meter (10 foot) rod has about 0.55 square meters in contact with the earth. A typical footing (0.5 m wide x 0.5 m deep) has that much surface area in 360 mm (14") of length. With a buiding that size, you have a wonderful connection to earth, even if the earth is a little sandy.
Drilling a deep well or driving a steel pipe or pile might do the same thing by giving more surface contact area and by hitting the lower resistivity layer below the water table.
RE: Deep Rod Earth Grounding
In Canada, a ufer can not be retrofitted. It must be a copper cable installed before the concrete is poured.
yours
RE: Deep Rod Earth Grounding
RE: Deep Rod Earth Grounding
Appear unusual that well has poor resistance. Is 600ohms(cm?) at 100'the resistance or resistivity? How this was measured?
Just a curiosity, does the meter is properly calibrated?
Did you compare your data with other facilities in the area?
RE: Deep Rod Earth Grounding
The problem with using metal water piping as part of the grounding system is that often the metal pipes are iron or a combination of copper, brass or iron. Put together two different metals in an aqueous solution, clamp an aluminum ground clamp on the cold wet ductile iron pipe, pass a little stray current through and presto now you have blue green water. Especially if the water is softened. Galvanized iron piping is the worst, and it only takes one little fitting to cause all the copper pipes to be pitted out in a couple of years.
They are supposed to install dielectric fittings where they join dissimilar plumbing materials to prevent this from happening. Unfortunately this occurs often at the main water service entry where the electrician installs a bonding jumper around the meter and voids the dielectric fitting anyway.
If you have 600 ohms resistance I would say that the plumber did his job and put in a dielectric. I'm just speculating but that sounds like the the resistance of the electrical path through the water inside the pipe.
Someone should tell the NFPA that many new water pipes are plastic nowadays.
RE: Deep Rod Earth Grounding
RE: Deep Rod Earth Grounding
Army Technical Manual 5-690 specifies a 1/0 copper ground ring at the bottom of a 10 foot deep trench and 10 foot ground rods driven to 10 feet below the bottom of the trench for lightning grounding. You could get the equivalent by connecting your existing ground rods to extensions using threadless coupling form Erico. However, the minimum diameter copper clad ground rod for use with couplings is 5/8 inch and if the soil is consolidated 3/4 inch needs to be used.
Your soil below 10 feet deep might actually be quite compacted due to the weight of the soil above and you could get a dramatic increase by extending your ground rods from 10 to 20 feet. Here is northeast Ohio, USA the top 6 feet of a ground rod driven from the surface of clay soil does not really act as a grounding electrode. Hence, some electricians drive a ground rod beneath the basement floor to access better soil.
RE: Deep Rod Earth Grounding
This system was completely seperate from the power system grounding electrode system which utilized Ufer grounding for the UPS,generators and switchgear.