Much before you install a Wire Earth Resistance Tester, the operator/engineer must have a decent understanding of the ground system being tested. The clamp-on measurement works perfectly fine in most situations but, like any other product, has some limitations, making it non-applicable in some configurations.
Clamp-on ground testing is a relatively new method to determine the ground system’s quality. It’s recommendable to use this device on sites where multiple grounds are placed in parallel. This technical piece will help you understand the various applications and outline whether the clamp-on method is viable or not, and even why!
Cable Towers, Utility Poles, and Meters
The more the earth is parallel with the electrode under test, the nearer measurement you will get to the value of actual earth resistance.
Therefore, the clamp-on method is ideally applicable to the Utility poles. The earth systems have several parallel-ground connections on the utility poles, which makes it an ideal location for the clamp-on method.
Likewise, another feasible application is to test the ground electrode resistance on a service entrance or meter. In such cases, there is a possibility of multiple earth paths, two electrodes, or maybe a connection to a water pipe, so you must ensure to identify the best positions to make a measurement.
One such similar application to utility pole electrodes is street lighting. There are chances that the clamps running to each street light’s electrode might be clamped, but you must ensure to clamp the right grounding conductor’s side.
The test ground electrodes on lightning protection is next on the list of practical applications for the clamp on test method. Lightning protection on any building is as effective as the grounding quality. In such cases, electrodes are normally placed at buildings in each corner with extra electrodes between larger buildings. Copper tapes conductors up to 50 mm wide are typically used. At times, it is difficult because the electrode is buried in a small pit. Besides, to allow two-wire continuity test application, many lightning protection down tapes are fitted with removable links. These removable links, also called jug handles, are time-consuming to remove. But they make ideal locations to use a clamp-on tester.
Using the clamp on method, you can test the Telephone pedestal ground electrodes. Cable sheaths are all connected to a ground bar, which is further connected to the ground electrode. Perform a test using the clamp-on around the cable connected to the ground bar to the electrode. Also, in cases when access is difficult, fit a temporary extension cable to facilitate fitting on the clamp-on tester.
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The street cabinet-flexibility points have another application to test the ground electrode installed inside primary cross-connection points.
Here, there may not be more than two parallel earth paths in series with the electrode. However, as per the calculations, if the clamp-on ground tester provides a measurement below 25Ω, then the electrode definitely would be somewhat below 25Ω.
If the rods are linked together by a ring that is buried beneath the soil, then the ground resistance measurement can’t be made. This configuration is common in cell towers and enables access somewhere above the ring.
These towers are grounded at the base, with each guy wire grounded. Also, all of them connected together in a ring of grounds. Also, note that if the operator clamps around the head of one of the guy wire grounds, the circuit will be completed simply in the ground ring, not through the soil but by the test current. This is because the test current circulates through the conductor connecting the individual elements consisting of the ring.
As such, the ground system quality won’t be tested by the clamp-on ground tester. The reading is of the loop resistance.
Use the clamp-on method to verify the Pad-mounted transformer ground electrodes. Sometimes, the user may have to clamp the electrode below the connections because of the number of connections to the same electrode. If these connections are to a large buried ground mat, the measurement will become a continuity measurement as the earth path will not be included in the test loop Fanserials.
Pole Mounted Transformer
Always keep in mind the golden rules of clamp-on testing, “there must be a loop resistance to measure”! Also, there are some occasions with utility poles where that loop is absent, not in places where you want it to be. Neither of the electrode sets is connected to an overhead earth cable. One of them is connected to the metal case of the transformer, while the other is connected to the start point of the LV secondary winding. But always remember that the resistance measurement is a fine combination of the two piles of earth in series.
At Besantek, you can get an accurate and reliable wire earth resistance tester. Also, don’t forget to check out the much-in-demand high voltage insulation tester, and other Test & Measurement Instruments, Tools, and High Voltage Phase Comparators.