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Although some engineers who regularly carry out installation testing prefer to use separate instruments for each of the main tests involved, the most popular solution is a multifunction tester. This provides, in a single instrument, facilities for all of the tests needed to certify an installation in line with current regulations. Modern multifunction testers are compact, dependable and easy to use.
Most of them don’t, but there are a few exceptions. Some of the latest tester, the MFT1720 for example, can check phase rotation and have facilities for testing three-phase RCDs in installations where a neutral is not available. When working on three-phase systems or indeed on single-phase systems close to the point where the supply enters the building, the CAT rating of the instrument needs to be given careful attention. In general an instrument rated CAT IV 600 V or better should be chosen, as this is safe to use on all parts of low voltage installations.
Almost all will offer facilities for measuring voltages and some for checking supply frequency. The latest models, however, like Megger’s new MFT1730, can also be used to measure earth electrode resistance. This is an increasingly common requirement in photovoltaic and other types of “green” energy systems and, indeed, in power installations. Another useful feature provided by some multifunction instruments is internal results storage, with facilities for Bluetooth wireless download to a laptop computer or even a smartphone. The best units of this type are complemented by software that automatically fills in the test certificates as the results are received by the laptop or smart-phone. This saves a lot of time as well as eliminating the errors that are almost inevitable when the certificates are filled out by hand.
Certification usually requires a test current of 200 mA. Changing to a lower test current, such as 20 mA, when not certifying will give a better battery life.