Insulation resistance test devices

The number of insulation resistance test devices available on the market is large, and the quantity of configurable features is overwhelming.

If you only want to run insulation tests on your device under test, a single test device is recommended. It contains only the single test method 'insulation resistance'.

If the device under test also requires a more comprehensive safety and function check, we recommend our multifunction test devices.

The insulation resistance test (also known as 'IR' test) serves to determine the insulation resistance in measurement ranges from kΩ to TΩ. Many test regulations (e.g., VDE, EN, IEC, UL …) prescribe the measurement and evaluation of insulation resistance.

Why the insulation resistance test is so important.

Washing machine, electric motor, luminaire … These and almost all other electrical products as well as electrical systems can only be operated safely if they have high electrical insulation strength.

Poor insulation can, in the worst case, lead to electrical accidents with severe injuries or even fatalities or cause significant product damage. With the help of the insulation test, you can determine the insulation quality of your device under test. The inspection of electrical products is run with test voltages typically from 500 to 1,000 V DC.

To cover almost all spaces of insulation testing, SCHLEICH provides a very extensive range of insulation test devices from 25 V up to 50,000 V DC.

Testing is performed between all current-carrying conductors and from current-carrying conductors to the housing. The insulation test fundamentally takes place between the same test connections as the high voltage test.

These faults are detected by the insulation resistance test.

• Insulation weaknesses between any electrical conductors and the protective earth conductor/device housing
• Insulation weaknesses between the electrical conductors
• Poor insulation on air and leakage paths

What are the pass/fail criteria?

The evaluation of the insulation test is always based on the ohmic insulation resistance, which is measured between the two poles of the TEST VOLTAGE. This must not fall below an adjustable limit.

Insulation test always with DC.

Fundamentally, the insulation test takes place with a DC TEST VOLTAGE.

Why?

Often, devices under test have unavoidable Capacitances due to filter capacitors or their physical design. A test with AC voltage would have the disadvantage that a high capacitive leakage current would flow through these Capacitances. The real resistance could not be determined precisely enough under such conditions. If, however, testing is performed with DC, Capacitance plays only a minor role. After charging the Capacitance, only a very small insulation current flows through the insulation resistance. Based on the applied voltage and the flowing current, the insulation resistance is calculated using Ohm's law.

This is how the insulation test is run.

Whether manually, semi-automatically or fully automatically: With SCHLEICH insulation test devices, all test tasks can be run quickly and efficiently.

They are all designed according to the "KISS principle". Following the motto: "Keep It Simple and Smart". This principle serves as a guiding theme for all SCHLEICH products.

For production facilities, semi- or fully automated insulation test devices or systems are more suitable. These are equipped with a relay switching field (relay matrix). This automatically switches the TEST VOLTAGE to the desired test points. A manual test is performed with a test probe. For this purpose, the operator guides the test probe by hand from test point to test point. Despite the manual process, the test can be documented flawlessly. A typical application is the inspection of electrical products, control cabinets, and machinery according to Machinery Directive EN 60204.

Test systems of this type have up to 1,000 test connections depending on the application.

Safe execution of the insulation test.

Working with high TEST VOLTAGES is not without danger. Therefore, appropriate safety regulations must be strictly observed. In SCHLEICH insulation test devices, the Test current is fundamentally limited. The built-in safety current limitation limits the Test current to a maximum of 3 to 12 mA DC. This makes it possible to operate the insulation test devices without test covers.

However, a second criterion must also be considered:
Due to their design, many devices under test have an unavoidable Capacitance. During testing, this Capacitance is 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 electrical shock after the test when touching the device under test due to the residual charge/Residual voltage.

If the test device is still connected to the device under test after completion of the test, the test device internally ensures safe discharge. However, if this cannot be reliably guaranteed, test covers, test cabins, light curtains, or barrier chains are used as protective measures.

Potential-free insulation test?

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

For high voltages from 15,000 V upwards, the TEST VOLTAGE, however, is usually single-side grounded.

What else you need to consider for an insulation test!

To correctly run the insulation test, it must be ensured that the device under test is actually connected to the TEST VOLTAGE. The proper execution of a Test can be monitored via two types of contact supervision:

• Specification of a charging current: This is advantageous for devices under test that exhibit Capacitance between the test points. If a measurable charging current flows when the TEST VOLTAGE is applied, it confirms that the device under test is correctly connected to the test device.
• Measurement of the voltage actually present at the device under test: For this purpose, two additional sense leads are connected to the device under test, supplementing the test leads. This type of measurement is often referred to as four-wire measurement. The TEST VOLTAGE actually applied to the device under test is measured via the two sense leads. This voltage is then compared with a predefined value. This control procedure is therefore called voltage feedback measurement.

What else is measurable with an insulation test?

In addition to the insulation test, the measurement of PI (Polarization Index) or DAR (Dielectric Absorption Ratio) is also possible. These are not typical safety test methods. However, they are frequently used for preventive maintenance.

The requirements for a standard insulation resistance test device.

Most national and international standards prescribe a TEST VOLTAGE of 500 V DC. Therefore, many SCHLEICH insulation test devices have a variably adjustable TEST VOLTAGE from 50 to 1,000 V DC.

They are typically equipped with a fast-reacting electronic DC TEST VOLTAGE source. Depending on the device, this also allows for the precise execution of voltage profiles.

SCHLEICH insulation test devices are based on over 30 years of experience. From the outset, digital measurement technology was used instead of analog. Fundamentally, the latest technologies are always applied.

How to find the suitable insulation resistance test device.

The number of insulation test devices available on the market is large, and the quantity of configurable features is overwhelming.

If you wish to exclusively run insulation tests, a single test device is the right choice. This contains only one test method, namely the insulation test.

However, if the device under test requires a more comprehensive safety and function check, we recommend our combination test devices/multifunction testers. These allow various test methods, such as insulation, high-voltage, and protective earth resistance test, to be conveniently combined in one device. The test method switch-over within the device ensures that no measurement leads need to be manually reconnected to the device under test during the Test.
Furthermore, the combination of safety tests and extensive function tests is also very common. For the function test, the test device additionally supplies the device under test with electrical operating voltage to also check its electrical operating characteristics.

Thanks to the intuitive and convenient operation of our insulation test devices, every Test is performed quickly, precisely, and cost-effectively.