Industrial environments and environmental influences on switchgear require increased demands on the respective components and their materials. With regard to terminal blocks, these specific requirements are defined in international norms and standards and the resulting test procedures. They relate to the insulating material and the electrically conductive metals and include material tests, stress tests, environmental tests and climatic tests.
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The glow wire test is used to verify the safety of the terminal blocks in the event of overheating or overloading. The plastic of the terminal block must be flame resistant.
For the test, a terminal block is fixed at right angles to the glow wire. With a temperature of 750° C and a force of 1 N, the glow wire presses in on the terminal block. A tissue paper pad is positioned under the test set-up, which must not be ignited by dropping plastic during and after the test.
The test is considered to have been passed if no inflammation of the tissue paper has occurred. Any flames or glowing processes that occur must be extinguished within 30 s after removal of the glow wire, i.e. te ≤ ta + 30 s.
The needle flame test demonstrates safe fire behavior in the event of direct contact with an inflammation source. The requirement for the fire behavior of a terminal block is a self-extinguishing plastic, which, in the event of a fire, neither promotes nor contributes to its acceleration.
For the test, an open flame, at an angle of 45°, is applied to an edge or surface of the terminal block. A tissue paper pad is positioned under the experimental setup, which must not inflame during and after the experiment due to dropping parts. The exposure time of the flame is 10 s, but 5 s for wall thicknesses below 1 mm or areas < 100 mm". After the flame has been removed, the afterburning time is determined, provided inflammation has occurred.
The test is considered to be passed if the burning time is < 30 seconds and falling burning or glowing particles do not inflame the tissue paper backing.
The aging test verifies the contact quality under simulated aging. Thus, the quality of the connections can also be ensured for a long life cycle of the terminal block.
For the test, 5 terminal blocks are mounted on a standard-compliant DIN rail and the terminal connection points are wired in series with the rated cross-section. The temperature range within the climatic cabinet alternates between 20 °C and 85 °C. The rated current flows between the heating phase and the 10-minute holding phase. This is followed by the cooling phase. The scope of the aging test includes 192 cycles, with the following after every 24th cycle, the voltage drop is measured over the total distance of the terminal block or protective earth terminal block and DIN rail.
The test is considered to be passed if the measured voltage drop for terminal blocks according to the 24. cycle maximum 4.8 mV or 1.5 times the voltage measured after the 24th cycle does not exceed the specified value. In the case of protective earth terminal blocks, the proof is deemed to have been passed if the measured voltage drop to the DIN rail is higher than the 24th cycle does not exceed 9.6 mV or 1.5 times the voltage drop measured after the 24th cycle in each case.
The proof of the TI value (temperature index) is used to determine the long-term thermal stability of electrical insulating materials. For example, the tensile strength (mechanical flexibility) of the plastic after storage at different temperatures can be used as a criterion.
For testing, the test samples are stored in a heating cabinet at at least three different temperatures. Test specimens (tensile bars) are taken at specified intervals and the tensile strength is determined on them. The values measured over the period (500 h to 5,000 h) are documented and extrapolated to 20,000 hours.
The temperature index in terms of tensile strength can be derived from the recorded time-temperature curve. This value corresponds to the time span of 20,000 hours with a property loss of 50% and allows statements to be made about the mechanical lifetime.
The RTI value (Relative Temperature Index) is used to determine the long-term thermal stability of electrical insulating materials. For example, the insulation resistance of the plastic after storage at different temperatures can be used as a criterion.
For testing, the test samples are stored in a heating cabinet at at least three different temperatures. Test samples are taken at specified intervals and the insulation resistance is determined from them. The values measured over the period (500 h to 5,000 h) are documented and extrapolated to 20,000 hours.
The relative temperature index with respect to the insulation resistance can be derived from the recorded time temperature curve. This value corresponds to the time span of 20,000 hours with a property loss of 50% and allows statements to be made about the electrical lifetime.
The verification of comparative tracking index or surface leakage resistance ensures the insulation strength of the surface of insulating materials under the influence of humidity and pollution.
For the test, a test sample consisting of the insulation material is fixed on the test table. Two platinum electrodes are placed on the test specimen at a distance of 4 mm and a defined test voltage is applied between them. 50 drops of a defined electrolyte solution are dropped between the two electrodes at intervals of 30 seconds and the creepage current is measured.
The test is considered to be passed if, at a defined voltage and application of the 50 drops, the measured leakage currents are less than 0.5 A. The applied voltage corresponds to the CTI (Comparative Tracking Index) value.
The "dry heat" climatic test verification ensures the contact quality of the connections and the safe operation of the terminal block after it has been exposed to the defined environmental conditions.
For the test, 5 terminal blocks are mounted on a standard-compliant DIN rail and the terminal connection points are wired with the rated cross-section. Depending on the material properties of the insulating material, the terminal blocks are subjected to thermal aging within the test cabinet at a defined time and temperature. For a terminal block made of the insulating material WEMID, such as WDU 2.5 or A2C 2.5, the defined values are 130 °C for 168 hours.
The test is considered to be passed if no damage has occurred to the terminal block after the test, further use is guaranteed and the measured voltage drop complies with the specified values.
The proof of the climatic test " Damp heat, cyclic" ensures the contact quality of the connections and the safe operation of the terminal block after it has been exposed to the defined environmental conditions.
For the test, 5 terminal blocks are mounted on a standard-compliant DIN rail and the terminal connection points are wired with the rated cross-section. The temperature range within the climatic chamber varies depending on the test severity for one or more cycles with a defined temperature and humidity.
-Class A defines a temperature range of +25 / +40 °C and a humidity of >93%
-Class B defines a temperature range of +25 / +55 °C and a humidity of >93%
The test is considered to be passed if no damage has occurred to the terminal block after the test, further use is guaranteed and the measured voltage drop complies with the specified values.
The proof of the climatic test "cold test" ensures the contact quality of the connections and the safe operation of the terminal block after it has been exposed to the defined environmental conditions.
For the test, 5 terminal blocks are mounted on a standard-compliant DIN rail and the terminal connection points are wired with the rated cross-section. In the test cabinet, the terminal blocks are exposed to a constant temperature of up to -65 °C for 48 hours.
The test is considered to be passed if no damage has occurred to the terminal block after the test, further use is guaranteed and the measured voltage drop complies with the specified values.
Storage in sulfur dioxide (corrosive atmosphere) ensures the contact quality of the connections and the safe operation of the terminal block after it has been exposed to the defined environmental conditions. In particular, the corrosive effect of sulfur dioxide as a component of polluted air on the connection points is the focus of laboratory testing.
For the test, 5 terminal blocks are mounted on a standard-compliant DIN rail and the terminal connection points are wired with the rated cross-section. In the climatic cabinet, the terminal blocks are exposed to 10 ppm concentrated SO2 gas at +25 °C and 75 % humidity for 10 days.
The test is considered to be passed if no damage has occurred to the terminal block after the test, further use is guaranteed and the measured voltage drop complies with the specified values.
Storage in hydrogen sulfide (corrosive atmosphere) ensures the contact quality of the connections and the safe operation of the terminal block after it has been exposed to the defined environmental conditions. In particular, the corrosive effect of hydrogen sulfide as a component of polluted air on the connection points is the focus of laboratory testing.
For the test, 5 terminal blocks are mounted on a standard-compliant DIN rail and the terminal connection points are wired with the rated cross-section. In the climatic cabinet, the terminal blocks are exposed to 1 ppm concentrated H2S gas at +25 °C and 75 % humidity for 10 days.
The test is considered to be passed if no damage has occurred to the terminal block after the test, further use is guaranteed and the measured voltage drop complies with the specified values.
Storage in salt spray ensures the contact quality of the connections and the safe operation of the terminal block after it has been exposed to the defined environmental conditions. In particular, the corrosive effect of salt spray as a component of polluted air on the connection points is the focus of laboratory testing.
For the test, 5 terminal blocks are mounted on a standard-compliant DIN rail and the terminal connection points are wired with the rated cross-section. In the climatic cabinet, the terminal blocks are sprayed with a defined amount of salt fog (NaCl 50 g/l +/- 10 g/l) at +35 °C for 48 hours.
The test is considered to be passed if no damage has occurred to the terminal block after the test and the measured voltage drop complies with the specified values.
In addition to the product-specific standards, there are a large number of other standards and certificates relating to the fire behavior of the insulation materials used. The railway industry in particular sets higher requirements here in terms of flammability and surface flammability, smoke generation, smoke gas toxicity and smoke gas density. But also in other industries, additional requirements are required for the raw materials and the products. A differentiation must always be made here as to whether the standard or certificate refers to the end product (terminal block) or to the raw material, such as the thermoplastic (plastics).
A certificate qualifies the respective raw material of the manufacturer and thus also flows indirectly into the end products, such as a modular terminal block. The following are some standards and certificates that the various raw materials of the Weidmüller terminal blocks meet and include:
| Fire protection on railway vehicles (EN 45545-2) | Smoke gas development generation (EN ISO 5659-2) Oxygen index (DIN EN ISO 4589-2) Toxicity of smoke gas (NF X70-100-2 (600°C)) |
| Flammability testing of plastics for parts in devices and applications | Vertical small flames test (UL 94 and EN 60695-11-10) Horizontal small flames test (UL 94 and EN 60695-11-10) |
| Standard for rail-based local transport and passenger transport systems | Surface inflammability ASTM E 162 Smoke gas development ASTM E 662 Smoke gas toxicity SMP 800 C |
| Halogen-free flame resistant | Halogen-free flame resistant (DIN EN ISO 1043-4) |
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