MIT515, MIT525, MIT1025, and MIT1525 insulation resistance testers
Measures up to 30 TΩ
Insulation resistance up to 30 TΩ at 15 kV, 20 TΩ at 10 kV, and 10 TΩ at 5 kV
Safety rated up to CAT IV
Up to 1000 V to 3000 m for the MIT1525, and CAT IV 600 V to 3000 m for the MIT515, MIT525, and MIT1025
Additional protection with dual-case design
A tough outer case to protect the tester, an inner fire retardant case, and IP65 rated when closed
Full set of diagnostic test modes
Including Polarisation Index (PI), Dielectric Absorption Ratio (DAR), Dielectric Discharge (DD), step voltage (SV), and ramp test








About the product
The MIT515, MIT525, MIT1025, and MIT1525 insulation resistance testers are compact, light 5 to 15 kV units for the diagnostic testing and maintenance of high voltage electrical equipment. They are ideal for original equipment manufacturers (OEMs) and industrial companies.
The MIT series has a full suite of test modes as well as on-board memory and the ability to stream data/download data to a PC/laptop. They also have rapid-charge batteries and operate from an AC source if the batteries are dead. Rapid charge batteries enable >60 minutes of testing after a 30-minute charge.
The MIT range includes:
- MIT515: 5 kV with IRT and DAR, but with no memory
- MIT525: 5 kV IRT with all test modes, including a ramp test plus advanced memory functions with recall to screen, RTC for time/date stamp of results, and USB drive to PC/PowerDB
- MIT1025: 10 kV IRT with all test modes, including a ramp test plus advanced memory functions with recall to screen, RTC for time/date stamp of results, and USB cable interface to PC/PowerDB
- MIT1525: 15 kV IRT with all test modes, including a ramp test plus advanced memory functions with recall to screen, RTC for time/date.
The MIT1525 is at the top of the range, and it performs insulation resistance tests up to 15 kV with a 30 TΩ maximum resistance and an accuracy of ±5 % from 1 MΩ up to 3 TΩ.
Safety rated to CAT IV, all these units are smaller and lighter than their predecessors, making them even easier to carry and store.
Technical specifications
- Max resistance reading
- 30TΩ
- Power source
- Battery
- Power source
- Mains
FAQs
The Polarisation Index is the ratio of insulation resistance at 1 minute to 10 minutes. It shows how the insulation is charging up and can determine whether it is clean and dry. For trending purposes, the PI value negates the effects of temperature compared to past results.
As the insulation value increases, the test current decreases and becomes harder to measure with the same level of accuracy.
The answer to this question depends on the test set you are using. It is certainly challenging for instrument manufacturers to produce test sets that deliver good performance when the guard terminal is in use, not least because the guard terminal diverts a lot of current away from the measuring circuits. It is by no means unknown, for example, to have a surface leakage resistance of the order of 0.5 MΩ in a test sample with an insulation resistance of 100 MΩ. In other words, the guard terminal current is around 200 times greater than the current in the measuring circuit. This high level of guarded current can cause many problems in a poorly designed instrument, including greatly impaired accuracy. If you’ve got such an instrument, there’s not much you can do about it. However, if you’re buying a new instrument, the answer is simple. Insist that the manufacturer gives you meaningful data about measurement accuracy when the guard terminal is in use. The latest Megger units, for example, have a maximum error of 2 % when guarding 0.5 MΩ leakage with a 100 MΩ load.
The current rating is important, as an underpowered instrument will take a very long time to charge high capacitive test objects, such as long cables; it may also be unable to maintain the required test voltage when high levels of surface leakage are present. It is, however, necessary to be careful when comparing different instrument current ratings. An instrument with a 3 mA short-circuit capability that incorporates power regulation technology to ensure maximum power transfer into all load types will, for example, almost always be faster and more convenient to use than a 5 mA rated instrument that doesn’t use this technology.
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.
If all you ever want to do is one-off type go/no-go testing, you’re correct to say that an instrument that tops out at a few GΩ is fine. But most people who carry out HV insulation testing are looking for more. Specifically, they want to be able to trend and compare results over time, as this provides a valuable warning of impending problems. Consider, for example, a piece of equipment that, over several years, has consistently had an insulation resistance of, say, 100 GΩ. However, the most recent test shows that this has fallen to 20 GΩ. Clearly, something has changed, and an investigation is in order. However, if you had carried out the tests with an insulation tester that reads “infinity” for all values above 10 GΩ, you would have noted no change, and no warning bells would have sounded!