What grounding to make in sandy soil?

27.05.15 , ,

Why sandy soil is special and why the question arouse: whether to do grounding in it or not?

The fact that the resistivity of soil, saturated or completely consisting of sand, can reach the value of 4000 ohm / m, which certainly can cause problems in the organization of grounding (see table below).

Sand, stronly wetted with groundwater	10 - 60 Ohm/m
Sand, moderately wetted	60 - 130 Ohm/m
Wet sand	130 - 400 Ohm/m
Dampish sand	400 - 1 500 Ohm/m
Dry sand	1 500 - 4 200 Ohm/m

^{Fragment from the table “Soil resistivity”}

Let's study the situation on a real example!

Task

Our technicians have recently received a request from Kazakhstan with the following task:

Perform calculations for the installation of protective grounding at the production and assembly site. According to the customer's data, the ground in the intended place of grounding devices installation is sandy. The resistivity, as has been described above, may have completely different values. Unfortunately, the exact soil resistance could not be determined on an unknown object. It turns out that we need to start from our own experience and take into account the maximum value.

We appeal to the regulatory documents:

in accordance with the EIC p. 1.7.103 and customer's data, the resistance of the grounding device at any time of the year should be not more than 10 Ohms in a linear voltage 380 in a three-phase AC source. In accordance with EIC p. 1.7.103. when specific soil resistance ρ > 100 Ohm • m , it is allowed to increase the indicated norms in 0.01 ρ times, but not more than tenfold.

Solutions

Below there are two options to solve this task:

Option 1. On the basis of modular grounding, ZANDZ ZZ-000-030 kit:

installation of two vertical electrodes 10.5 m long and one vertical electrode 9 m long, united by a horizontal electrode of stainless steel copper-plated corrosion-resistant tape with the cross-section of 30x4 mm. Depth of the tape burial 0.5 m;
to the wall of the building a horizontal ground electrode 2 meters long is being laid (copper-plated tape with cross-section 30x4 mm).

Arrangement of elements of grounding device is shown on the figure below

Option 1. On the basis of modular grounding, ZANDZ ZZ-000-030 kit

Вертикальный заземлитель – vertical ground electrode

Горизонтальный заземлитель – horizontal ground electrode

Holding the calculations in accordance with the existing norms of ground resistance, we obtained the following values:

1) at the ground resistivity 200 Ohm • m = 7.26 Om, which is less than the required 10 Ohm;
2) at the ground resistivity of 2000 Ohm • m-72.56 Om, which is less than 100 ohms, acquired in the result of norm increase coefficient in 10 times (in accordance with EIC p. 1.7.103).

Both values obtained are less than critical, which means installation of modular grounding kit ZZ-000-030 is justified and meets the requirements described in the task.

List of required materials:

№	Fig.	Product item	Item	Quantity
1.		ZZ-000-030	ZANDZ Universal grounding kit (30 meters)	1
2.		GL-11075-50	GALMAR copper-bonded tape (30 * 4 mm / S 120 mm²; coil of 50 meters)	1

Option 2. Electrolytic grounding, ZANDZ ZZ-100-102 kit in the soil 2000 Ohm ∙ m:

installation of one kit of electrolytic grounding ZANDZ ZZ-100-102;
from the horizontal mesh, a horizontal ground electrode 4 meters long is laid (copper-bonded tape with cross-section of 30x4 mm) to the wall of the building. Laying depth 0.5 meters;
in connection with the formation of a talik zone in the form of an oval 6x3 m in size, electrolytic grounding electrodes should be placed at the distance from each other (not less than 6 m at a parallel mounting of electrodes) from the foundations of buildings and other engineering structures. Arrangement of elements of the grounding device is shown on the figure below:

Option 2. Electrolytic grounding, ZANDZ ZZ-100-102 kit in the soil 2000 Ohm ∙ m

Зона талика – talik zone

Комплект электролитического заземления – electrolytic grounding kit

After the calculation,the device ground resistance was determined - 77.83 ohm, which is less than 100 ohm, recieved in the result of the coefficient of rate increases in 10 times.

So, the installation of a set of electrolytic grounding ZZ-100-102 is also justified and meets the requirements described in the task.

List of required materials:

№	Fig.	Product item	Item	Quantity
1.		ZZ-100-102	ZANDZ electrolytic grounding kit (horizontal; 3 m)	1
2.		GL-11075-10	GALMAR copper-bonded tape (30 * 4 mm / S 120 mm²; coil of 10 meters)	1

See also:

Video of Design of a Public Building in Moscow

Lightning Protection System for Observatory Located on Pip Ivan Mountain Using GALMAR Equipment

GALMAR Lightning Arresters To Protect Flat Roofs and Equipment

GALMAR GL-20035 Lightning Discharge Counter