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Earth Tester Basics

This page covers Earth tester basics and mentions earth resistance testing. It covers Earth ground tester manufacturers or vendors.

In broad terms, "earth resistance" is defined as resistance of soil observed in the path of flow of electric current. In general, Earth is relatively poor conductor of the electricity in comparison to normal conductors such as copper wire. Resistance can be very low when area of the path where current is flowing is larger in size. Hence in this condition Earth is considered as good conductor.

It is important to know earth resistance as it helps in finding the location which is ideal to ground the equipments and help to protect human beings. It also helps to determine what lies at few distance below the earth's surface.

Earth resistance testing

The Earth resistance testing will help find the best earth location and depth to fix low resistance electrodes. The resistivity of earth is used to indicate degree of corrosion useful in underground pipelines. These pipelines are used for oil, water, gas etc. Typically, locations with low resistivity values will have higher corrosion.

In earth resistance testing, earth tester generates AC signal. This signal is fed to the SUT (System Under Test). By measuring flow of current and generated voltage will give us system resistance. The earth resistance can be measured in the range between 0.001 to 20 KOhm.

earth resistance testing

Figure depicts concepts of earth resistance testing employed in earth tester equipments. As shown in the figure, Rod-3 is moved and measurement of voltage and current is recorded at various points between Rod-1 and Rod-2. By using Ohm's Law (R = E/I), Earth resistance can be determined at various points and location having low resistance can easily be derived from the plot(earth resistance versus distance in feet of Rod-3 from Rod-1.

Following are the three test methods used to measure Earth resistance.
• Fall of potential method OR three terminal test method
• Two point test method or Dead Earth method
• Clamp on test method

Earth ground tester manufacturers or vendors

Following are the popular Earth Ground Tester manufacturers or vendors:
• Megger
• HIOKI E.E. CORPORATION
• Fluke Corporation
• Meco Instruments Pvt. Ltd.
• Global Instruments
• Yokogawa
• Cambridge Instruments & Engineering Co.
• FLIR Commercial Systems (Extech Instruments)
• Motwane Manufacturing Company Pvt. Ltd.

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