Insulation resistance testers

There is a wide variety of insulation resistance testers available on the market, and the number of configurable features is overwhelming.

If you intend to perform only insulation tests on your test object, a single-function tester is the best choice. It supports only the "insulation resistance" test method.

If the test object also requires a more comprehensive safety and functional check, we recommend our multifunctional testers.

The insulation resistance test (also known as the “IR” test) is used to determine insulation resistance in the range from kΩ to TΩ. Many testing standards (e.g., VDE, EN, IEC, UL, etc.) require the measurement and evaluation of insulation resistance.

Why insulation resistance testing is so important.

Washing machines, electric motors, light fixtures… These and almost all other electrical products and systems can only be operated safely if they have a high level of electrical insulation resistance.

In the worst-case scenario, poor insulation can lead to electrical accidents resulting in serious injury or even death, or cause significant damage to the product. Insulation testing allows you to determine the insulation quality of your test object. Electrical products are tested using test voltages typically ranging from 500 to 1,000 V DC.

To cover virtually all areas of insulation testing, SCHLEICH offers a very comprehensive range of insulation testers from 25 V up to 50,000 V DC.

The test is performed between all live conductors, as well as between live conductors and the enclosure. The insulation test is always performed between the same test terminals as the high-voltage test.

These faults are detected by the insulation resistance test.

• Insulation failures between any electrical conductors and the protective conductor/equipment housing
• Insulation defects between electrical conductors
• Poor insulation in air gaps and creepage distances

What are the criteria for "good" and "bad"?

The insulation test is always evaluated based on the insulation resistance, which is measured between the two terminals of the test voltage. This value must not fall below a preset limit.

Always perform insulation testing with DC.

Generally, the insulation test is performed using a DC test voltage.

Why?

Test objects often have unavoidable capacitance due to filter capacitors or their physical design. Testing with AC voltage would have the disadvantage that a high capacitive leakage current would flow through these capacitors. Under such conditions, the actual resistance could not be determined with sufficient precision. If, on the other hand, testing is performed with DC, capacitance plays only a minor role. After the capacitance is charged, only a very small insulation current flows through the insulation resistance. The insulation resistance is calculated using Ohm’s law based on the applied voltage and the current flowing.

Here's how the insulation test is performed.

Whether manual, semi-automatic, or fully automatic: SCHLEICH's insulation testers allow you to perform all testing tasks quickly and efficiently.

They are all designed according to the "KISS principle"—that is, following the motto: "Keep It Simple and Smart." This principle serves as the guiding philosophy for all SCHLEICH products.

For manufacturing facilities, semi- or fully automated insulation testers or automatic test systems are more suitable. These are equipped with a relay switching panel (relay matrix). This automatically routes the test voltage to the desired test points. Manual testing is performed using a test probe. To do this, the operator moves the test probe by hand from test point to test point. Despite the manual process, the test can be fully documented. A typical application is the testing of electrical products, control cabinets, and machines in accordance with the Machinery Directive EN 60204.

Depending on the application, test systems of this type can have up to 1,000 test ports.

Ensure that the insulation test is performed correctly.

Working with high test voltages is not without risk. Therefore, it is essential to strictly adhere to the relevant safety regulations. On SCHLEICH insulation testers, the test current is always limited. The built-in safety current limiter restricts the test current to a maximum of 3 to 12 mA DC. This makes it possible to operate the insulation testers without test hoods.

However, a second criterion must also be taken into account:
Due to their design, many test objects have an unavoidable capacitance. During the test, this capacitance becomes charged and stores the charge. The maximum stored energy must not exceed 125 mJ (Q = 1/2 x C x U²). Otherwise, the operator could receive a dangerous electric shock from the residual charge/residual voltage when touching the test object after the test.

If the test equipment is still connected to the test object after the test is complete, the test equipment ensures safe discharge internally. However, if this cannot be reliably guaranteed, protective measures such as test hoods, test booths, light curtains, or barrier chains are used.

Potential-free insulation test?

In most applications, potential-free insulation testing is used. It is typically used with test probes rated up to 1,000 V DC or safety test guns rated up to 10,000 V DC. It ensures the highest level of safety for the user.

In contrast, for high voltages of 15,000 V and above, the test voltage is typically grounded on one side.

Other things to keep in mind when performing an insulation test!

To perform the insulation test correctly, it must be ensured that the test object is actually connected to the test voltage. Verifying that the test has been performed correctly can be done using two methods of contact monitoring:

• Specifying a charging current: This is beneficial for test objects that have capacitance between the test points. If a measurable charging current flows while the test voltage is being applied, you can be sure that the test object is properly connected to the test equipment.
• Measurement of the voltage actually applied to the test object: To do this, two additional sense leads are connected to the test object in addition to the test leads. This type of measurement is often referred to as a four-wire measurement. The test voltage actually applied to the test object is measured via the two shunt leads. This voltage is compared to a reference value. This verification procedure is therefore called voltage back-measurement.

What else can be measured during an insulation test?

In addition to insulation testing, it is also possible to measure the PI (polarization index) or the DAR (dielectric absorption ratio). These are not typical safety testing methods. However, they are frequently used for preventive maintenance.

Requirements for a standard insulation resistance tester.

Most national and international standards specify a test voltage of 500 V DC. For this reason, many SCHLEICH insulation testers feature a test voltage that can be set between 50 and 1,000 V DC.

They are typically equipped with a responsive electronic DC test voltage source. Depending on the device, this also allows for the precise execution of voltage profiles.

SCHLEICH insulation testers are based on over 30 years of experience. From the very beginning, the company has relied on digital rather than analog measurement technology. We always use state-of-the-art technologies.

Here's how to find the right insulation resistance tester.

There is a wide variety of insulation testers available on the market, and the number of configurable features is overwhelming.

If you only want to perform insulation tests, a single-function tester is the right choice. It includes only one test method: the insulation test.

However, if the test object requires a more comprehensive safety and functional check, we recommend our combination testers/multifunction testers. These devices conveniently combine various test methods—such as insulation, high-voltage, and protective conductor resistance testing—into a single unit. The test method switching function in the device ensures that no test leads need to be manually reconnected to the test object during the test.
In addition, the combination of safety tests and comprehensive functional tests is also very common. For functional testing, the tester additionally supplies the test object with operating voltage to verify its electrical operating characteristics.

Thanks to the intuitive and user-friendly operation of our insulation testers, every test is performed quickly, accurately, and cost-effectively.