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srinivas231
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Join Date: Jun 2011
Posts: 10

Design of Earthpits

06/16/2011 5:41 AM

HI friends

I want to know how to design required earthpits in a place? is this based on load or area of cross section.

thanks

srinivas

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PWSlack
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#1

Re: design of earthpits

06/16/2011 5:55 AM

Follow the codes applicable in the country of installation.

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spradhan
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#2

Re: design of earthpits

06/16/2011 6:02 AM

Refer IS:3043

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#3

Re: Design of Earthpits

06/16/2011 9:18 AM

http://cr4.globalspec.com/thread/69229 Does the link helped you?
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electricalexpert65
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#4

Re: Design of Earthpits

06/16/2011 10:12 AM

First step is knowing the soil resistivity of the location where you are planning to install the earth pits.

Second step is to decide whether you are going to install Pipe Earth Electrode or Plate Earth Electrode or Rod Earth Electrode or Strip Earh Electrode.

Having decided the above, what is the dimension of the earth electrode?

There are formulae in Standards to calculate the individual earth electrode resistance for each of the above types of earth electrodes. Calculate that for the earth electrode that you have chosen to install.

Decide what is the net earth resistance you want to have for your system.

The number of earth pits required = desired earth resistance / resistance to earth of the individual earth electrode.
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Anonymous Poster #1
#5
In reply to #4

Re: Design of Earthpits

06/16/2011 11:55 AM

Confused with the formula given.Can you give little more explanation on parallel connection and how the formula support it.
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srinivas231
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#6
In reply to #4

Re: Design of Earthpits

06/16/2011 11:37 PM

formula is confusing, could you pl tell clearly

if desired resistance is 1 ohm , resistance of earth of individual is 4 ohms

then required earthpits is = 1/4 , hope some confusion in formula

also if we considered 4 earthpits in parallel i will get 1 ohm, same 4 earthpits will withstand entire area pl explain
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PWSlack
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#7
In reply to #6

Re: Design of Earthpits

06/17/2011 3:55 AM

It depends upon the spacing of the electrodes. If they are less than one electrode-length apart, multiplying the number of earth rods does not give a similar divisor to the resistance.

The country code still needs to be followed, "off topic" or not.

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Vinu_Answers
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#8

Re: Design of Earthpits

06/18/2011 5:55 AM

Dear Srinivas231,

In order to design or establish earthing system in any place, you need to consider the following things:

1) Purpose Of earthing.

2) Different types of earthing systems as per IS-3043 (TNS, TNC, TNCS, TTNS, TT etc.).

3) Soil resistivity of area where earthing system is to be installed. If the

4) Type of earthing electrodes and material.

5) Size of the earth electrode, refer http://cr4.globalspec.com/comment/737522

6) Calculation of net earth resistance of the system

7) Decide no. of earthpits.

The number of earth pits required = desired earth resistance / resistance to earth of the individual earth electrode.

8) If necessary, go for artificial treatment of Soil.

Pl. refer IS-3043 for better and clear undeerstanding.

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spradhan
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#9

Re: Design of Earthpits

06/20/2011 1:06 AM

"The number of earth pits required = desired earth resistance / resistance to earth of the individual earth electrode."

I would say both "electricalexpert65" & "Vinu Answers" are correct except the above formula as mentioned in their respective posts.

The correct formula is:

No. of earth pits = resistance to earth of individual earth electrode /Desired overall earth resistance.

This is because all the interconnected earth electrodes are in parallel.

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srinivas231
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#10
In reply to #9

Re: Design of Earthpits

06/21/2011 12:35 AM

thank you, but if individual earthpit resistance is 2 ohms if i want desired resistance of .5ohms i need only 4 earthpits for a plant is it correct

srinivas
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spradhan
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#11
In reply to #10

Re: Design of Earthpits

06/21/2011 8:26 AM

You are right; a minimum of 4 earth pits will suffice in case the individual EP resistance is 2 ohms.

Depending upon the layout of your plant you may increase the No. of EPs which will further reduce the overall resistance of the plant.But make sure that the distance between the adjacent EPs is more than twice the length of the electrode for ensuring optimum use of each EP.

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mmdqadir
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#12
In reply to #10

Re: Design of Earthpits

01/29/2014 12:52 AM

First u have to check the earth resistivity in ur plant .
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spradhan
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#13
In reply to #12

Re: Design of Earthpits

01/29/2014 11:53 PM

You are right.This value is required to work out the resistance of each earth electrode as per the formula appearing in IS:3043.This can be measured through testing at the given site or it may be readily available from the drawings/documents of the existing plant.

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Anonymous Poster (2); electricalexpert65 (1); mmdqadir (1); PWSlack (2); spradhan (4); srinivas231 (2); Vinu_Answers (1)

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