A hand-wound insulation tester would be the most common form of Test Instrument that would be carried by the 1980s electrician which would appear to be something from a bygone age to the apprentice of today.

To test in line with the current 18th Edition IET Wiring Regulations four main tests are required:

One of the most important developments to affect all types of electrical test equipment has been the introduction of safety category ratings in line with IEC1010. Usually known as CAT rating. This relates to an instrument’s ability to withstand transients (spikes) on the supply. This is important because if, while the instrument is being used, it experiences a transient that is beyond its capacity to handle, it is likely to be seriously damaged and may even injure the user.

Other important developments applicable to all test instruments include increasingly robust construction and, in some cases, weatherproofing. Older instruments were much more susceptible to damage than the latest models.

The latest models are also much more robust electrically, and unlike predecessors will not be damaged if connected to a live circuit when carrying out a dead circuit test such as an insulation or continuity test. The best MFTs like the Di-Log DL9118 will in fact resist damage even when connected to a three-phase supply after a dead circuit test has been selected and locked down.

Finally, many instruments of all types are now able to store test results for later downloading to a computer, a tablet or even a smartphone. That might sound like a luxury, but it really isn’t, as modern software can enter the downloaded results directly into a test report. This not only eliminates the tedious and time-consuming work of report forms but also means the end of transcription errors.

Now let’s look at the individual tests starting with continuity testing. Continuity testing has been around in one form or another since the earliest days of electricity, with the simplest form being no more than a bulb and a battery. Today, rather than using a separate continuity tester most contractors use the continuity test function built into a multi-function tester or an insulation tester.

Even with something as simple as a continuity test, significant progress has been made over the past 40 years. The best continuity tester now offers auto start, which saves a lot of time, especially when working at heights and keeping one hand firmly on the ladder. Some models allow the test current to be selected with a low current of 10mA for general work to preserve battery life and a high current of 200mA for certification work conforming to BSEN61557.

Insulation is a vital part of any electrical installation. Therefore, it is no surprise that insulation testers have been around since the early 1900s. Today’s modern instruments are very different to the earlier models with analogue needle movements and their hand-cranked handle generators. The best more advanced models have dual digital bargraph and digital displays which are particularly useful as the stability of the insulation resistance tells an experienced user a lot about any potential issues.  In some cases, issues can be easily identified with the segmented bargraph display, as opposed to the exact value of the insulation resistance, which a value symbolised in Meg Ohms is required for completing the test report and is much easier to read on a digital display.

Other useful features offered by the latest insulation testers include a test-lock function and remote switched probes that allow convenient two-handed testing. More advanced instruments incorporate a sounder to provide an audible indication that the insulation has passed alerting the user of any potential issues.

Earth loop impedance testing is carried out to ensure that, should a fault occur in an electrical installation, enough current will flow to operate the fuse or circuit breaker. The objective is to make sure the circuit is disconnected fast enough to prevent the overheating and possibly a fire

The loop testers that have generally been available for around 40 years use a high current test, typically 10 amps. The benefit of a high current is that the test can be carried out quickly and the test results are unlikely to be influenced by electrical noise on the circuit.

A high current loop test does have one big drawback, if the circuit is protected by an RCD or RCBO, which most installations have these days, the protective device will trip. To overcome this problem modern loop testers have been developed that will use much lower test currents, typically milli amps. Which will not trip the RCD or RCBO. Other recent developments in loop testing include dual displays that simultaneously show loop impedance and prospective fault current.  The latest Loop Testing Technology fitted to the Di-LOG DL911x Series MFT’s eradicates RCD Uplift and reduced noise interference, enhanced noise monitoring systems that alert the user to noisy supplies and built-in lead resistance compensation that makes it unnecessary to check the lead resistance before carrying out every test.

Instruments to test RCDs to ensure that they operate correctly when called on to do so, but are not subject to nuisance tripping when no wiring fault is present RCD Testers first started to become more common around 40 odd years ago, and once again there has been substantial improvements in functionality over the years. Automatic testing has proved to be a huge time saver.

Without this, the user would have to walk between the tester and the RCD to reset it on each occasion for 4 of the six tests that have to be performed on each RCD. With auto test the user simply initiates the whole sequence once, then walks to the RCD and resets it each time. The user does not need to return to the instrument until the whole sequence of 6 tests is completed. Which saves a lot of time.

Among other important features that the latest RCD testers provide are facilities for testing the wide range of RCD types that are now coming into use. Particularly in green energy installations. As well as time delayed RCDs, Ramp test facilities help trace problems with nuisance tripping.

Modern instruments provide the user with safety and performance features which makes their job safer, easier and quicker. At Di-Log we are constantly working to develop instruments that remain at the forefront of technology.

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