While specialist equipment is essential for electrical testing in some parts of industry, many everyday requirements can be satisfied with the same equipment that’s routinely used to test building installations. However, this does hinge on whether the tester has been chosen wisely. Megger’s Simon Wood explains

Multi-function testers designed for general purpose installation testing and handheld insulation test sets are also useful for testing industrial installations. This is because most of the electrical installations in a typical factory closely resemble the installations found in commercial and domestic premises. And, of course, all UK installations have to conform to the same requirements laid down in the IET Wiring Regulations.

However, there are some factors that are essential to take into account when choosing instruments for industrial use. For example safety – industrial installations are likely to be subject to a higher level of transients than commercial or domestic installations and testing is more likely to be carried out near to the source of supply. This makes the instrument’s IEC 61010 CAT rating particularly important.

For industrial use, instruments should be rated CAT IV 300V or better for connection to low voltage systems without additional protective devices. This means they are safe for connection anywhere on the system right up to the source transformer.

It’s tempting to think that CAT ratings are relevant only for instruments that are routinely used for live circuit tests and not instruments like insulation testers that should be used only on dead circuits. However, it’s important to remember that most modern insulation testers have ancillary functions like voltage measurement, which are used for testing on live circuits. Even if the instrument doesn’t have these functions, it’s easy to accidentally connect a dead-circuit tester to a live circuit. An appropriate CAT rating is therefore essential for all types of instrument.


While many parts of industrial electrical installations are similar to those in commercial and domestic properties, there are parts that are significantly different. In particular, the use of 3-phase supplies is common. Lack of 3-phase facilities limits the usefulness of older multi-function installation testers in industry, but not the latest models. The best of these can check phase rotation, fully test three-phase RCDs without neutral connections, and carry out phase-to-phase loop and PSCC tests.

The better multi-function testers also provide extra facilities that are of frequent use in industrial applications. These include the ability to measure the resistance of earth electrodes, to test the less common types of RCD, including programmable types, and to accurately measure earth leakage currents. Some of these options may require the use of accessories, but these accessories always cost much less than a specialist instrument.

Insulation testers

Turning to insulation testers, a handheld instrument with an appropriate CAT rating, capable of testing at 250, 500 and 1,000V will be suitable for much of the testing required in industry. The instrument must, however, give meaningful readings up to very high insulation resistance values – ideally 100GO or more.

This is because trending insulation resistance values over time gives an excellent indication of the true state of insulation. If the values are falling consistently, investigation is necessary, even if the actual insulation resistance value is above the ‘minimum acceptable’ value. Only numerical results can be trended and ‘infinity’ isn’t a number, so a tester that reads infinity for all values above 1GO wont provide any indication that insulation has fallen in resistance from, say, 20GO to 5GO, even though such a large fall suggests that there is a problem.

In industrial applications, an insulation tester with facilities for dielectric absorption ratio (DAR) and polarisation index (PI) testing is even more useful, as these tests provide results that can be compared with known typical values for a specific item of equipment, such as a motor. DAR and PI values are also largely independent of temperature. Note, however, that these values are derived from insulation resistance measurements, so it is still important that the instrument can meaningfully measure high values of resistance.

For instruments to be used in industry, there’s another important aspect to consider – ruggedness. No one ever intends to drop an instrument or to use it where it will get splashed with water, but these things happen. Therefore, if the instrument is to have a long life, it must feature rugged construction and a good ingress protection rating – IP54 is ideal.


When their versatility is taken into account, the best multi-function installation testers and handheld insulation testers offer outstanding value for money and, as we’ve seen, they are eminently suitable for a wide range of industrial testing applications. So, if you buy or specify test equipment for industrial use, don’t neglect contractor type products. Chosen wisely, they provide a lot of functionality for surprisingly little money.



T: 01304 502 101