Safety without compromise:
Designed to endure the harshest environments and conditions, we also build our insulation resistance testers with safety in mind to ensure the protection of both users and equipment.
When the world’s leading electrical experts need the tools to get the job done right, they go with Megger. That’s because as the industry experts, we design our insulation testers to address every critical challenge that may arise, throughout the complete lifecycle of the asset. From commissioning and installation to transportation and repairs, you can trust our in-depth knowledge and top-of-the-line products to empower your decision-making.
That depends upon the size, complexity, and criticality of your equipment. Even identical units can differ in the required check periods; experience is your best guide. In general, however, working apparatus – such as motors and generators – are more likely to develop insulation weaknesses than wiring, insulators, and the like. A test schedule for working equipment should be established, varying from every 6 to 12 months, depending on the size of the equipment and the severity of the surrounding atmospheric conditions. For wiring and the like, tests once a year are generally sufficient unless the installation conditions are unusually severe.
The answer, at least in part, is in the question! An insulation resistance tester is designed to be used only on dead circuits, but that’s no guarantee that it won’t ever be accidentally connected to a live circuit. And if it is, an appropriate CAT rating is essential, especially as the environments in which HV insulation testers are most frequently used often have high supply transients. We recommend a CAT IV 600 V rating, and it’s imperative to be sure that this rating applies to all of the instrument’s terminals, including the guard terminal.
There are several reasons to select a test set with a high output current. Possibly the most important is that a high output current means that the item under test will be charged more quickly, which means that the test can be completed in a shorter time and also that there’s less risk that the readings will be taken before the test voltage has had time to stabilise properly. And, if you’re using the instrument’s guard terminal, don’t forget that a lot of output current may well be diverted via the surface leakage of the item under test. Unless the instrument has a high output current capability, this could mean that the output voltage will collapse, and the test results will not be valid.
First, decide on the type of testing you need to perform. If it’s routine go/no-go testing and you don’t need data storage, an Essential instrument (MIT515) will likely be a cost-effective choice. Consider an Advanced instrument (MIT525, MIT1025, MIT1525) for more versatility and/or internal data storage. And if working in extremely electrically noisy environments or need high charge/burn currents, an Expert instrument (S1-568, S1-1068, S1-1568) will be right. Having decided on Essential, Advanced or Expert, choose the instrument that will deliver the maximum test voltage needed.
Take a deeper dive into electrical insulation testing solutions through our comprehensive guides.
Learn the guidelines for evaluating results of resistance tests.
Learn the ins and outs of insulation in our complete guide.