exp1EarthResistanceCheck.docx - EARTH ELECTRODE RESISTANCE...

EARTH ELECTRODE RESISTANCE & SOIL RESISTIVITY
MEASUREMENT WITH MEGGER EARTH TESTER
Ex.No: 01
OBJECTIVES:
1. To get familiar with the working of an earth-tester.
2. To measure the Earth resistance and
3. To find the soil Resistivity
APPARATUS REQUIRED
S.No Description Range Type Quantity
1. Hand driven Earth Tester (1–100 )Ohms AC 1
2. Spikes - - 4
3. Hammer - - 1
4. Wire stripper - - 1
5. Connecting Wires As Req.
Measurement of earth resistance using fall of potential method
Theory
All the electrical installations and appliances should be earthed properly to
prevent damage to the equipment and ensure human safety. A separate wire, known as
earth wire runs along the supply line and is ultimately connected to the ground through
an earth electrode. The total resistance of the earthing system should be small so that
in the event of any fault the fault current is sufficiently high to blow off the fuse.
Also, the fault current should be properly conducted to earth via the electrode.The
resistance of the earth electrode system consists of three components.
They are
 Resistance of the electrode materials and connections to them
 Contact resistance between the electrode and the soil surrounding it
 Resistance of the surrounding earth.

These resistances are as shown in Fig. Generally, the resistance of the surrounding
earth will be the largest of the three components. Hence, earth electrode resistance is
the earth resistance.
Consider Fig.1 which shows the effective resistance areas (concentric shells) of the
ground electrode X and the auxiliary current electrode Z. The resistance areas overlap.