Ground rod question.

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  #1  
Old 04-18-14, 10:02 PM
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Ground rod question.

Ive been told that its best to drive in a ground rod near a drainage soak away or somewhere where theres a lot of moisture in the soil..
Well the problem is that the land here is practically solid limestone so driving a ground rod in is practically impossible..
This is my idea.. Would it produce a good ground?
We are digging out a septic tank.. My idea is to build up a corner section with hollow blocks inside the tank 12"X 12" in the first chamber put the rod in and pack it in with soil.. The blocks are porous so the soil should be constantly moist/wet..
What you think? Would that work OK?

Also,Ive just been doing a bit of reading about "Ufer ground" which is basically connecting the ground wire to the foundations..
http://en.wikipedia....iki/Ufer_ground
Cant do that as no exposed rebar now to foundations..
Would connecting the ground wire to the rebar in the underground water tank be OK?
The tank is concrete rebar reinforced.
We are in the Philippines and I doubt I have to worry about code as most buildings here dont have earth wires.
 
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Old 04-19-14, 05:58 AM
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I'm not sure about moist soil filling a former septic tank. I think you can achieve equivalent grounding but it is tricky. Theoretically it is the same as moist soil amidst buried broken concrete and rocks out in the open. A possible problem is tar or similar waterproofing on the inside or outside of the tank that eliminates the needed conductivity. If it is really a cesspool (made of unmortared untarred blocks) rather than a septic tank then filling it in with the ground rod inside will work well. (Being made of bare solid concrete does not disqualify it from being a septic tank simply due to concrete's porosity.)

Here is the tricky part. An "official" concrete encased electrode needs, I think, 20' worth of embedded rebar. So you could not just enclose one corner of the septic tank for a 4 to 6 foot rod and get equivalent performance. And real ground rods need to be 8' long to meet the U.S. standard. Since you are not in the U.S. you might get away with four 4' rods instead of two 8' rods and get equivalent performance although not meet the U.S. code (National Electric Code).

One thing worth researching is how and when to use horizontal ground rods when it is impossible to drive vertical rods down 8 feet. This is probably the least expensive and most straightforward method.

Using the rebar of a buried concrete water tank will qualify as a concrete encased (grounding) electrode.

For either the filled in septic tank ground rod or the water tank rebar, you will need to provide adequate physical protection for the ground wire (grounding electrode conductor) from rototillers, etc. such as bury it at least 2 feet down if there is any distance between the tank and the building.

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OT:

CCE and Ufer are used interchangeably nowadays but a true Ufer grounding system may or may not require more than one concrete encased electrode possibly in different locations depending on soil moisture. The NEC specifies one CCE (one connection to rebar) for a home if there is any below grade reinforced concrete, or no mandate for buildings constructed before a certain date which I don't recall.

The NEC gives requirements for grounding electrodes that must be followed as a minimum (in the U.S.) but may or may not actually achieve state of the art lightning protection. (There is no such thing as absolute lightning protection.) I believe that the true standard for lightning protection is a 25 ohm or less impedance between the electrical grounding system (panel neutral bus, grounding electrode conductors, related metal objects. etc.) and the earth as measured by equipment specially intended for the purpose. After installing two 8' ground rods, you don't need to measure let alone meet the 25 ohm standard.
 

Last edited by AllanJ; 04-19-14 at 07:21 AM.
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Old 04-19-14, 07:16 AM
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I can only reference what is done in the US. Since you are in the Philippines things may be done different.

The ground rod is only for high voltage events such as lightning, as Allan posted. The ground in a circuit should never carry current except during a fault, and the fault will go back to the source which is the main panel.

Follow Allan's suggestions of laying the ground rod in a shallow trench. I would not worry too much about the soil being moist as I would guess the Philippines gets quite a bit of rain.
 
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Old 04-21-14, 01:16 PM
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OK,thank you so much for taking the time..Very much appreciated.
One more question. I`m not sure if I can find un insulated number 6 copper wire here.. Is insulated wire OK to hook up to the ground rod?
If not,I guess we can burn the insulation off..
 
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Old 04-21-14, 01:35 PM
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The NEC allows both insulated and bare to the rod.
 
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