What is Earth Resistance
What is Earth Resistance
(OP)
I have two questions regarding earth resistance;
1.For single electrode R=(rho)/2(pi)[1/r] ->here why ressitivity of copper rod (material -copper) has not considered,but only resistivity of soil is considerd?
2.For concrete encased electrode,earth ressitance less than rod alone-How since concrete has a higher resistivity equivalent to dry soil
thanx in advance
Abraham
1.For single electrode R=(rho)/2(pi)[1/r] ->here why ressitivity of copper rod (material -copper) has not considered,but only resistivity of soil is considerd?
2.For concrete encased electrode,earth ressitance less than rod alone-How since concrete has a higher resistivity equivalent to dry soil
thanx in advance
Abraham






RE: What is Earth Resistance
However the resistance of the rod is negligible.
A stainless steel rod of ¾” diameter and 20’ length presents only 0.0015 ohm and the minimum grounding resistance in a very low resistivity soil it is more than 1 ohm.
The tolerance of soil resistivity measurement it will be more than the rod resistance.
According to IEEE 80/2013, indeed, the concrete specific resistance [resistivity] it is between 30 Ω-m to 200 Ω-m. There are other publications which consider this resistivity between 6-10 Ω-m. The soil resistivity could be between 10 to 100 [usually].
For a high resistivity soil a moisturized concrete will reduce the grounding resistance, of course.
By-the-way the grounding resistance of a rod directly buried is:
R=ro/(2*PI()*L)*(ln(4*L/a)-1) [in excel form]
ro=earth resistivity L =rod length a=rod radius
[IEEE 142/2007 Table 4-5—Formulas for the calculation of resistances to ground.
For concrete embedded electrode-see E.J.Fagan-and other- formula:
Res=k*(roe*(ln(8*length/2/conrad)-1)+roc*(ln(8*length/2/rodrad)-1)- roc*(ln(8*length/2/conrad)-1))
k=1/(2*pi()*length)
length-gounding rod length; conrad=concrete cylinder [around the rod] radius; rodrad=rod radius
roe=soil resistivity; roc=concrete resistivity.
See:
G-THE USE OF CONCRETE ENCLOSED REINFORCING RODS AS GROUNDING ELECTRODES by E.J.Fagan and others.
RE: What is Earth Resistance
RE: What is Earth Resistance
One question can I ask witout strating another thread;
Is there any thumb rule for distance between HV and LV Earth pits?for 11k,allowable GPR is around 300V as per IEEE ,I read.
But if there is any distance to be maintained by thumb rules something called "zone of influence.
thanx in advance
Abraham
RE: What is Earth Resistance
RE: What is Earth Resistance
https://library.ukpowernetworks.co.uk/library/en/g...
that is my concern.
best regards
Abraham
RE: What is Earth Resistance
The low voltage cables supply the consumers and from the transformer-earthed on substation area-has to be insulated from low-voltage side and the secondary side has to be earthed far from substation limits in order to avoid transfer potential.
There is a number of possibility how to combine or separate the low-voltage and high-voltage electrodes according to BS 7430. See: 19.2 General earthing arrangement of substations.
RE: What is Earth Resistance
RE: What is Earth Resistance