Although metal theft is a common problem, in some instances it may not always be apparent until something goes wrong. Therefore, as Megger’s Damon Mount explains, routine testing is vital in order to minimise the risk

While the theft of some metals may be noticed immediately, when something like an earth conductor is stolen it may not be picked up straight away and it can leave electrical installations in an extremely hazardous state.

According to the website www.metaltheftuk.com metal theft is now costing the British economy more than £800m per year. However, it is far from an issue that is simply confined to Britain, and the increasing world demand for metals and the resulting escalation in prices has seen metal theft become increasingly prevalent in virtually every country of the world.

While metals of all types are targeted (even ferrous metals that would, until recently, have hardly been worth the effort of stealing) the prime target is copper, as it is in huge demand, currently commanding an exceptionally high price. As recently as February 2009, copper was priced on world markets at just $1.51/lb but, at the time of writing, the price is edging ever closer to $4/lb. Small wonder then, that the theft of copper cables and other conductors is now commonplace.

When cable theft leads to the signals not working on a stretch of railway or the power going off in a village, it is evident immediately that something is wrong. However, the theft of conductors from earthing systems, for example, would be less readily apparent, but still have the potential for causing disruption and danger.

Stealing this type of conductor is particularly attractive for better informed miscreants who realise that the level of danger involved in the theft is minuscule compared with, for example, taking a hacksaw to a live power cable. And, of course, it may be some time before the theft is noticed, as removing part, or even all of an earthing system may not necessarily produce effects that are immediately obvious.

Consider, for example, an earthing system that has the sole function of protecting a building against lightning. If this is removed, there is nothing to indicate that there is a problem but, of course, the building and possibly its occupants are at risk. Equally, if the earthing system for a small wind turbine or other renewable energy installation is plundered, the installation may apparently continue to work normally, although, in fact, much of its protective equipment may now be inoperative.

Inspection and testing

A schedule of routine inspection and testing of earthing systems at regular intervals would negate this problem. Visual inspection will, of course, reveal the most obvious problems, but there’s another approach that, in many situations, is quicker, more convenient and more certain, and this is to use a clamp type earth tester.

Designed for use in installations that have multiple earth electrodes, these so-called stakeless earth testers are very quick and easy to operate. The user simply clamps the jaws around the connection to the earth electrode or a conductor such as an earth tape, presses a button to initiate the test and, within a few seconds, a reading of resistance is shown. The tester measures the continuity of a circuit, so providing there is a return path, the instrument will measure the resistance of the electrode and the conductors connected to it. This works equally well for continuity measurement of conductors in an interconnected bonding system. As it is a quick and easy test to do, it can be done at multiple locations in the system to check the continuity of many earth conductors.

Unlike traditional earth electrode testing, there is no need to disconnect any part of the earth installation to carry out the test. This saves time and helps to ensure that safety is not compromised, as it can be when earth electrodes need to be disconnected for testing.

If the results obtained from the test are within the expected range, then there is little concern over metal theft, and no further investigation is required. However, this obviously leads to the question of how the ‘expected range’ is defined. One answer is that a very high result should immediately sound a warning. A much better answer is that the result should not be hugely different from the one obtained the last time the measurement was made.

This shows the importance of regular testing and recording of results, so that anomalies can be spotted quickly and easily. It is nevertheless important to remember that the results from consecutive tests are unlikely to be identical, as earth electrode resistance is affected by factors like the amount of moisture in the soil at the time the test is carried out, and this can change significantly. A difference in a comparison of current and past measurements could be an indication that something may be amiss – an open circuit reading where there wasn’t one before will show that it’s likely conductors are missing.

Summary

Let’s be honest, earth clamp testers are not a solution to the problem of metal theft but they do offer a fast and convenient way of detecting when such thefts have taken place in earth installations, thereby allowing prompt remedial action to be taken before the theft can lead to injuries to people or damage to equipment and property.

Megger

www.megger.com

T: 01304 502 100