© 2007 ideal industries 1 of 12 basics clamp-on ground resistance tester

Basics Clamp-on Ground Resistance Tester© 2007 Ideal Industries www.idealindustries.com 1 of 12

Basics Clamp-on Ground Resistance Tester


Integrity of the Ground

• Three key components of the single ground Electrode– Resistance between

Ground Electrode and Clamp, Bonding in multi-rod applications

– Resistance of contact between soil and rod(s)

– Resistance of Concentric Shells of earth



• Effect of the Soil on Electrode resistance – Soil conditions, and soil types

• Sandy soil have higher resistance that clay or loam

– Seasonal Environmental conditions which effect both moisture and temperature



• Ground Electrode– Typically measured only at installation

• In truth very seldom tested by installers.

• Only one out of 10 said they test single point ground Electrodes, in an informal survey

– Methods of testing the ground electrode• Fall potential test, and Slope method

• Ground resistance clamps


Test Equipment

Clamp-On Ground resistance tester.

• The Resistance of the total ground network is now measured.

• This is a loop tester and requires the utility return to act in simples terms as the aux rods.


Test Equipment


• Make sure you have a clean, clear connection of the clamp around the ground.

• Select and measure the current, if current is > 5 (this my very from manufacture) resistance can’t be measured using the ground clamp tester.


Test Equipment


• If voltage (E) is applied to any measured grounding probe R(X) through a special transformer , current (I) flows through the circuit and can be measured , thereby establishing an equation which can be used to calculate R(x)

– E/I=RX. If E is kept constant, then through the use of a CT current can be detected and the resistance of the ground electrode circuit my be achieved.


Clamp-On Ground Resistance Measurement

• R1, R2, ---Rn can be considered as a large parallel resistive circuit. As we know, a large number of resistors in parallel with each other effectively create a resistance value which is lower than the value of the least resistive path.

– Here is an easy to understand example of parallel resistance. – Simple equation, 1/R = 1/R1 + 1/R2 + 1/R3 + 1/R4.

– If R1=3.5, R2 =4, R3 = 4.5 and R4= 5,– then 1/R=0.285 +0.25 + 0.22 + 0.2, or R= 1.04 ohms.


Clamp-On Ground Resistance Test

• Advantage is that the ground electrode doesn’t need to be disconnected from the electrical system.

• The jaws of the clamp must be placed in the electrical path of the systems grounding wire to the ground rod


Clamp-On Ground Resistance Test

• This is an example the Clamp-On Ground tester is being used to measure the ground resistance in a street light application

• Note in this application the tester is place between the ground conductor and the ground electrode. The loop is between the ground conductor and the parallel path of R1, R2 ---Rn back through the earth resistance.


Earth Testers

• Ideal/Megger 61-788 – 3 pole Testers

• IDEAL/Megger 61-789– 4 pole Testers– Self powered - no need

for hand crank– Low power consumption

Compact and lightweight– Quick battery check– Limited lifetime warranty


Earth Testers

• Ideal 61-920 Ground resistance Clamp – Ground Resistance

– Ground Leakage Current

– Auto ranging

– Audible indication < 40 ohms

– Open jaw indication

– Data hold

© 2007 ideal industries 1 of 12 basics clamp-on ground resistance tester

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