What is Earth Tester : Construction, Applications, and It Types

The earth resistance testers are invented by Sydney Evershed on 13th January 1861 and Ernest Blacker Vignoles in 1950. This tester is used to measure the resistance value of the earth. There are different types of testers are available in different sizes and ranges to measure the resistance. The best earth tester is “Extech 382252 earth ground resistance tester kit”. The range of this tester ranges from 20 ohms to 200 ohms & the cost of this tester is 42,801.15/-. We all know that the energy from the sun is very crucial for good health. This article discusses an overview of earth tester, types of earth tester, and its applications.

What is Earth Tester?

Definition: The earth tester is one type of equipment, used to measure earth resistance. If the earth resistance value is very low then this tester is also known as ground resistance tester. The best tester is “Extech 382252” because it is simple to use and provides accurate readings.


We all know that the energy from the sun is crucial for good health. When we make direct contact with the surface of the earth, our body receives a charge of energy that makes us feel better, this is called earthing. In past days, people observed natural energy from the sun but nowadays everyone lives in the houses, even we go outside we wear shoes that prevent us from connecting, because of this reason we feel tired because of ever touching the earth.

Nowadays, we can connect earthing indoors by simply connecting the earthing port to the switch, which directly connects to the existing ground out of our home. This connection is safely and conveniently receiving earth energy from where ever you are, whether you are working, playing and especially while you are sleeping, because of this earthing you feel better. There are different types of earthing they are plate earthing, pipe earthing, rod earthing, and strip or wire earthing. The resistance of any earthing system depends mainly on the shape of the earth electrode, material of the electrode used under test, and depth in the soil.

Need of Earthing

The needs of earthing are

  • To protect human lives from leakage current
  • To provide safety to electrical appliances or devices
  • To keep the voltage constant

Electrical Earthing

Earthing is important for people so to make earthing, dug 2 to 3 meters deep hole in the ground near house and place a thick copper plate of dimensions 50cmx50cm in the hole. Here the copper plate is welded to the thick copper rod which is protected by a hallow insulating pipe. After placing the copper in the ground, cover that place with a mixture of charcoal and salt to make a good connection with the earth.

The plate is buried in the ground and the copper rod is connected to the house and is called the earth. The electrical power from substations is supplied to the house through line wire and the neutral wire. The schematic of an electrical circuit with an appliance in the house is shown in the below figure.


In the above figure, there is no earthing. The line wire carries current from the source. For example, the battery to the appliance and the neutral wire carries it back to the battery. But in a faulty appliance, if the circuit comes in a contact with the metallic casing which causes an electric shock to the person by touching it because high current flows through him to the ground.

Schematic-Diagram-of-An Electrical Circuit-Using-Earthing
schematic-diagram-of-an electrical circuit-using-earthing

To prevent shock, the metal casing is connected to the earth wire. If there is a fault in the appliance, the electric current from the metallic body into the ground or earth prevents electric shock. In an electric plug, we have a line, earth, and a neutral connection, which is used to make a connection to the appliances.

Procedure to Measure Earth Resistance by AET 23 Meter

The most important precautions to be taken before starting the measurement is

Step1: Disconnect the electrode from the load so that we can get the actual value of the earth.

Step2: Insert the current spike at a distance of 30 meters from the electrode. This distance is considered as 100% of the distance for this test.

Step3: Insert the potential or voltage pipe at a distance of 62% of 30 meters between the electrode and current spike. As per Dr.Tagg, when a potential spike is inserted at a 62% distance in the total distance between the electrode and current spike, we get stable results for earth resistance.


  • Take the tester AET 23, now connect ‘E’ terminal of the tester to the earth electrode under test.
  • Connect the ‘P’ terminal wire of the tester to the potential spike.
  • Connect ‘C’ terminal of the tester to the current spike.
  • After connections are done, now select the proper range of 20 ohms by rotating the knob switch of AET 230 meter.
  • After selecting the initial range, press the test button of the meter. When we press the test button, the AC current flows from electrode to potential spike from the soil. The voltage between ‘E’ (Electrode Under Test) and the ‘P’ (Potential Spike) is measured by the meter.

The above figure shows the connections from the meter to the electrode, potential spike, and current spike. This is the working principle of earth tester AET 23

Types of Earth Tester

The types of earth testers are clamp-on ammeters or clamp meters, leakage current clamp meters, ESD meters (Electrostatic Discharge Meter), 3-terminal and 4-terminal ground resistance meters, and soil PH meters. The explanation of these testers is discussed below.


Types of Testers Description


1. Clamp-on Ammeter This meter is used to measure the current flow through a conductor. This meter increases efficiency and productivity Digital Clamp Meter SE-DT266, Fluke 303/EM ESP Clamp Meter, Fluke 302 Clamp Meter, Meco Auto-ranging Digital Clamp Meter, Ms2001f Mastech Clamp Meter
2 Leakage Current Clamp-On Meters This meter is used to measure the leakage current in-ground Fluke 369 FC Leakage Current Clamp Meter, Fluke AC Leakage Current Clamp, Metravi Digital Leakage Current Meter Model DT-4671
3. ESD Meters (Electrostatic Discharge Meter) This meter is used to measure static electrical charges RS PRO Surface ESD Tester, Desco Europe Ioniser Surface ESD Tester
4. Three Terminal Ground Resistance Meters This meter measures earth ground systems KUSAM-MECO 3 Terminal Earth Resistance Tester, KM 2030, Megger  DET3TC 2 and 3 Terminal Earth Resistance Tester, Megger DET3TD 2 and 3 Terminal Earth Resistance Tester, Megger DET4TD2 2,3 and 4 Terminal Earth Resistance Tester
5. Four Terminal Ground Resistance Meters This meter measures earth resistance Waco Analogue Dual Range Tester 4 Terminal, Waco Digital Earth Resistance Tester 4 Terminal, CIE 222M Three Range Hand Driven 4 Terminal Earth Tester, CIE-222 M 4 Terminal Earth Resistance Tester
Soil PH Meters This meter measures the soil PH level. The PH measuring range is 3.5 to 9.0 AUS soil tester, 3-in-1 PH meter test kit, Jainco PH Meter

Construction of Earth Tester

The earth tester uses the dc generator, rotational current reverser, rectifier, and potential coil. The main parts of this tester are current reverser and rectifier, these two parts are mounted on the dc generator shaft. This tester consists of two pressures coils like p1 and p2 and two current coils like C1 and C2. These two coils are placed across the permanent magnet. Both the pressure and current coils have two terminals, the one end of both coils connected to a rectifier and other ends are connected to earth electrodes.

The potential coil is connected to the dc generator directly and it is placed between permanent magnets ‘N’ and ‘S’. The pointer coil position is fixed on the calibrated scale. The magnitude of the resistance is indicated by the pointer. The resistance of the earth is defined as the ratio of potential to earth electrode and current, or the ratio of voltage and current. The circuit diagram of the earth tester is shown below.


The different power station’s earth resistance values are shown below.

Large Power Stations: In large power stations, the earth resistance value is 0.5 ohms

Major Power Stations: In major power stations, the earth resistance value is 1.0 ohms

Small Sub Stations: In small substations, the earth resistance value is 2.0 ohms and in all other cases the value of earth resistance is 8.0 ohms.

Applications of Earth Tester

The applications of earth tester are

  • Pad and Pole mounted transformers
  • Cell towers
  • Street lights and street cabinets
  • Lightning protection
  • Telephone pedestals


1). Which material is best for earthing?

The best materials for earthing are GI wires and copper.

2). How many ohms are required for proper earthing?

One ohm or below one ohm is required for the proper earthing.

3). What is earth resistance value?

The earth resistance value is 5 ohms or less than 5 ohms.

4). What will happen if the earthing is not done?

If earthing is not done properly, all the household appliances will damage.

5). How do you identify an earth wire?

We can identify the earth wire by color, the color of the earth wire is green or yellow.

In this article, the overview of earth tester meter, earthing, applications, construction, it types, and the procedure to measure earth resistance by AET 23 meter is discussed. Here is a question for you, what is strip or wire earthing