Things to consider when looking at a multifunction installation tester.
These days, most electrical contractors prefer multifunction testers (MFTs) to carry out installation testing. There are plenty of models to choose from, and it’s tempting to think that there’s not a lot of difference between them. That’s definitely not true! The best instruments, like the new models in Megger’s MFT1700 range, include features that will save you time and money, as well as letting you tackle a wider range of jobs without needing additional equipment.
What are the differences that matter? Let’s start with safety. A CAT IV 300 V safety rating in line with IEC 61010 is important as it means you can work on any part of an installation without having to carry out a risk assessment about the level of supply transients present. But that’s not the only aspect of safety you need to consider.
The way the instrument behaves if it’s accidently used incorrectly is also important. It’s all too easy to connect a tester to a live circuit when it’s set for a dead-circuit test. When this happens, a Megger MFT1700 range instrument will provide both audible and visual warnings. It will also terminate the test, even if it’s been locked on. Crucially, there will be no damage to the instrument or, even more importantly, to you.
Next, think ease of use. With Megger MFTs large selector knobs with clear colour coding make test selection quick and easy. That may seem a small point, but having to navigate through multiple menus every day not only wastes time but also soon becomes very annoying. And easy test selection reduces the risk of making a mistake, especially when working under pressure.
A clear, easy to read display is another important feature, and a dual display that also includes an analogue arc is even better. But why do you need those extras? A dual display means you can see at a glance not only the main result – insulation resistance, for example – but also a secondary parameter, which, in the case of an insulation test, would be the test voltage. This means you can be absolutely sure you’re carrying out the test under the right conditions.
And the analogue arc – which is definitely not the same as a bar graph – is invaluable to see what’s happening when the test results are changing rapidly as they might do, for example, if the insulation of the circuit you’re testing is starting to fail.
Let’s move on to things that can save you time and trouble when you’re carrying out specific tests, such as loop testing. It’s a big benefit to have a full range of loop test options – high current for circuits that are not RCD protected, non-trip three-wire for the majority of applications, and non-trip two wire for those awkward tests where there’s no neutral available. Having the right loop test readily available for every application is a big time saver.
Another proven time saver is automatic RCD testing, which means you can carry out the whole sequence of tests prescribed for an RCD without having to walk back and forth between the instrument and the RCD to initiate each separate test. Of course, with the growing use of RCDs with unusual sensitivity ratings, a programmable RCD test function is invaluable, and an RCD ramp test function could save you a lot of trouble and frustration when you’re dealing with cases of nuisance tripping.
Megger’s new instruments offer another very useful feature – automatic Zmax. With this, you don’t have to remember or write down the Zs values as you check every socket on a ring since the instrument automatically identifies and stores the highest value you measure. When you’ve finished your tests, the Zmax value is already displayed for you to enter it on the test certificate
You’ll definitely welcome autostart for continuity, loop and RCD testing. This means that the test starts automatically when you apply the probes to the circuit, without you needing a third hand – which, let’s face it, few of us have – to press the test button. If you use a switched probe with the Megger instruments, insulation testing also becomes a two-handed test
Another difference that really matters is the versatility of the MFT. Many contractors are now starting to work on renewable energy systems, vehicle charging points and industrial installations. Naturally, they’ll want an MFT that can cope, which is why Megger now offers models that can measure earth electrode resistance (earth electrodes are often found in renewable energy and vehicle charging systems), test B-type RCD’s and carry out tests on three-phase installations.
The MFT1721 can, for example, check phase sequence, evaluate prospective short-circuit current up to 20 kA, perform phase-to-phase loop testing at 415 V, and test three-phase RCDs even when no neutral connection is available. The MFT1731 offers the same functionality and, when it is used with appropriate accessories, it supports a choice of two-pole, three-pole, stakeless and ART (attached rod technique) methods for measuring earth electrode resistance.
Clearly the latest MFTs have a lot more to offer than older types so, if you haven’t replaced your tester in a few years, it’s very probable that investing in one of the new Megger instruments will make your life a lot easier as well as increasing the range of jobs you can tackle.
To find out more about the MFT1700 series of multifunction installation tester. click here