Getting Down to Earth 51Limitations of Stakeless TestingThe clamp-on tester is only effective in situations with multiple grounds in parallel. It cannot be used on isolated grounds, as there is no return path. In addition, it cannot be used if there is an alternate lower resistance loop not including ground. Fall-of-potential testing is advised for installation checks or commissioning new sites. General ground testing rules apply, e.g. if another part of the ground system is in the “sphere of influence” of the electrode under test, the result will be lower than the true resistance of the electrode. A low return path is required for readings that approximate a fall-of-potential test result on a particular ground connection. A high resistance return path will yield high readings. The point of clamping the tester must be on the correct part of the loop for the electrode under test, as a wrong connection may give a faulty reading. The operator must have a thorough understanding of the grounding system to know exactly what is being measured. The method is susceptible to noise from nearby electrical apparatus and older instruments are less effective for very low resistance grounds. A final disadvantage of the clamp-on ground tester is that there is no built-in proof for the method without disconnection and performing a fall-of-potential test. As noted previously, a clamp-on ground tester should not be the only ground test instrument used. It is, however, an important part of the ground testing tool kit, along with a fall-of-potential tester. The clamp-on tester can be used to identify problems quickly. A fall-of-potential tester can then be used to confirm those problem results. This approach, together with trending results, allows the operator to be more productive and improves the early detection of potential faults.Cell Tower Ground TestingCommunication towers present a problem where clamp-on testers perform well if used correctly, but measure ‘dead shorts’ if not. The problem is that the tower is live and provision of services prohibits removal of power. In America, utilities typically provide a low impedance utility
