CONSTRUCTION & MEASUREMENT OF EARTH PIT RESISTANCE

LIST OF CONTENTS:

 

1.     Introduction

2.     Earth pit construction

3.     Internal diagram of earth pit

4.     Measurement of earth resistance

5.     Connection diagram of det 20

6.     Conclusion

 

INTRODUCTION:

Electricity is dangerous and getting electrocuted can be fatal. This is because our body conducts electricity. Insulation is therefore a very essential part of using electricity and electrical appliances at home and earthing is something that is done to prevent us from getting an electrical shock.

The un-insulated parts of electrical devices used in the house and those present in and around electrical fittings, circuits and receptacles are connected to the earth to prevent electrical shocks in a number of different ways. All these put together form that is known as earthing.

The earth is an even better conductor of electricity than our body that why earthing of electrical circuits is done so that if equipment have poor insulation or short-circuit, in that case electrical leakage current  passes into the ground instead of through us when we touch the appliance/wire/receptacle in question.

Electrical earthing is of two types. When earthing is used only to protect us from getting electrocuted it is called protective earthing. Protective earth wiring carries current only when appliances/circuits have malfunctioned and exists to keep the electrical potential of the earth and appliances equal. Fuses blow and circuit breakers trip when electricity passes through protective earth wiring.

In functional earth, more than just shock protection is done. Functional earth wires carry electricity even during the normal functioning of the devices like surge suppressors and electromagnetic interference filters and help them operate properly.

In the electrical plug of each appliance at home, there are three wires, and one of these is the earthing wire. Earthing wire is in the top pin in 3-pin plugs. In 2-pin plugs, it is intertwined with the neutral. Not only at home are electrical systems earthed, but even transformers that supply to your house are earthed.

The main receptacle that distributes power to all the sockets at home definitely needs to be earthed and this is what the earthing pit or earth chamber is present to do. The receptacle itself receives power from transformers.

Made usually of concrete and having a removable cover (for checking and mend works), the earth pit essentially has a long copper rod that goes into the ground and is connected to the receptacle via wiring. This electrode is further insulated with gravel, sand and coal.

 

EARTH PIT CONSTRUCTION:

 

1. Excavation on earth for a normal earth Pit size is 1.5M X 1.5M X 3.0 M

2. Use 500 mm X 500 mm X 10 mm CU Plate (Plate may be used as big as possible to

Contact more and more area of Earth for low resistance & best result)

3. Make a mixture of Wood Coal Powder Salt & Sand all in equal part

(a) Wood Coal Powder use as good conductor of electricity, anti-corrosive, rust prove for

GI Plate for long life.
(b) Salt use as electrolyte to form conductivity between GI Plate Coal and Earth with

humidity
(c) Sand has used to form porosity to cycle water & humidity around the mixture

4. Put GI Plate (EARTH PLATE) of size 500 mm X 500 mm X 10 mm in the mid of mixture
5. Use Double GI Strip size 30 mm X 10 mm to connect GI Plate to System Earthling
6. It will be better to use GI Pipe of size 2.5" diameter with a Flange on the top of GI Pipe to

cover GI Strip from EARTH PLATE to Top Flange .

7. Cover Top of GI pipe with a T joint to avoid jamming of pipe with dust & mud and also use

water time to time through this pipe to bottom of earth plate
8. Maintain less than one Ohm Resistance from EARTH PIT conductor to a distance of 15

Meters around the EARTH PIT with another conductor dip on the Earth at least 500 mm

deep.

9. Check Voltage between EARTH PIT conductor to Neutral of Mains Supply 220V AC 50 Hz it should be less than 2.0 Volts

 

INTERNAL DIAGRAM OF EARTH PIT:

  

 

MEASUREMENT OF EARTH RESISTANCE:

 

We are measuring the Earth resistance with the help of DET 20

 

The earth electrode (C1 earth pit) whose resistance to be measure must be disconnected

from its connection to site.

Putting the two auxiliary electrode(P2 & C2)  in the earth in straight line with Earth electrode C1 (earth pit) for correct measurement in such a way that the distance between the auxiliary electrode P2  and Earth electrode (C1) is 62 %  of the distance between auxiliary electrode C2 & Earth electrode (C1 earth pit).Shown in fig.

Now short the terminal of electrode C1 & P1& press the start button in right side of meter and read out the value of earth pit Electrode Resistance.

 

FORMULA FOR PLACING AUXILIARY ELECTRODE IN EARTH WITH RESPECT TO EARTH PIT ELECTRODE

   DISTANCE BETWEEN C1&P2 = 0.62 * DISTANCE BETWEEN C1 & C2

 

Note :Minimum Distance  between C1 & C2 is 100 feet

 

CONNECTION DIAGRAM OF DET 20:

 

 

CONCLUSION:

 

With the help of cu plate and mixture of salt, sand & wooden coal powder we can make earth pit and This type of earth  pit resistance is in the range of 1 to 5 Ohms can we achieve.