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AEMC 3731 Ground Tester

AEMC 3731 Ground Resistance Tester. One month rental price $ 250.
Tests via the Clamp-on method with transmit & receive current clamp.
AEMC 3731 Ground Tester
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Earth Ground Resistance Testers for measuring ground resistance and resistivity. We'll help you choose. 

Ground Test Diagram

For a good simple clamp-on type tester use the AEMC Tester model: 3731. Clamp-on types are convenient in some situations, but may not give reliable results as the 3P Fall-of-Potential method.

The tester is clamped around a ground conductor, usually on the cable that is connected to a ground rod, and close to the ground rod. It uses two coils, one generates a voltage (an E-field) at a frequency typically in the range 2 – 3 kHz. The E field induces a current into the grounding system which is sensed by the second coil which measures the induced current.  From Ohm’s law, the tester can calculate the impedance from the E and I values. 

Be aware of the limitations in distributed ground systems.  The clamp-on type tester is typically used to test the grounding plate (butt-plate) of power poles.  The grounding system as a whole must be taken into account since the pole being tested, Rx, shares a ground “path” with other power poles in the neighborhood, represented by R1 to RN.  Or in the case of a pylon, the other three legs plus other pylons in the neighborhood. The method has been applied to distributed ground systems, such as a buried ground grid for buildings; a good example is that of a data center whereby the grounding grid, usually a mesh of conductors, or a long conductive loop around the perimeter, is buried in the ground or in the foundation. A grounding electrode (ground rod) is connected to the grounding grid and it is at this connection point that the ground tester can be clamped to test ground resistance.

Note 1:  This method requires that a path for current must exist – it should not be used to measure an isolated, free-standing, ground rod; i.e. if the ground rod is not connected by a cable to the grounding grid. 

Note 2:  The induced field is an alternating one so using the tester with long lead lengths may cause incorrect measurements because the self-inductance of the leads will interact with the alternating fields creating inductive reactance (e.g., higher ohmic values will occur).

Note 3:  The tester should be placed around the ground rod and close to the soil. 

The Fall-of-Potential method ideally should be used for individual ground rods and when distance and space permits. When this is impracticable use the clamp-on tester.

Read: Application note on the Fall-of-Potential method.

Not sure what approach to take? Then please talk to us before you buy or rent, call: 408 988 1346