Mechanical tests for terminal blocks

This mechanical test defines the connection of standard conductors according to the manufacturer's information. Terminal blocks must be designed in such a way that conductors
with the documented rated cross-section and the rated connection capacity can be connected. The specifications are documented by the manufacturer in metric (mm²) and imperial values (AWG). Rated cross-section means: The value of the maximum possible cross-section of all connectable conductors (flexible, single or multi-stranded) that certain thermal, mechanical, and electrical requirements refer to. Rated connection capacity means: The range encompassing the largest to the smallest connectable cross-section (reduced by at least 2 increments) and the number of connectable conductors for which the terminal block has been designed. During the test, the terminal blocks are connected with the rated cross-section and the rated connection capacity. Alternatively, the rated cross-section can also be verified using gauges. (See Fig.) It must be possible to freely insert conductors or gauges into or connect them to the open terminal point. Terminal blocks from Phoenix Contact offer dimensions for the defined rated cross-section that are well above the standard. Thanks to appropriate design measures, the rated cross-sections can also be connected with a ferrule and insulating collar in all terminal blocks of the CLIPLINE complete system.

Electrical installations and plants must also afford a high level of safety when carrying out maintenance or during measuring and testing tasks. BGV A3 prescribes the voltage-free state of the affected low-voltage system parts up to 1,000 V AC and 1,500 V DC for general work in the vicinity of live parts. To prevent electric shock, live parts must be secured against direct contact through the use of covers or barriers. The terminal blocks from Phoenix Contact therefore offer electrically skilled persons and instructed persons touch protection based on EN 50274. During testing based on EN 50274, the test probes are led from the operating direction to the test object. Electrical contact between the test probes and live parts must not occur. Finger contact safety is tested with a test force of 10 N and back-of-hand safety at 50 N. Phoenix Contact terminal blocks are mainly designed in accordance with DIN EN 50274. For more detailed information, please refer to the product documentation.

Correctly wired terminal blocks must offer a high degree of mechanical safety. This includes reliable connection of the conductor. Therefore, tests are performed with rigid and flexible wires with the smallest cross-section, with the rated cross-section, and with the maximum cross-section. A vertically fixed terminal block is connected to a conductor. A test weight corresponding to the cross-section is attached at the end of the conductor. The conductor is fed through a central 37.5 mm aperture in a rotating disc and turned on its own axis 135 times. This procedure must not damage the clamping area on the conductor. Afterwards, the contact must pass a conductor pull-out test. Terminal blocks from Phoenix Contact are designed to ensure that the conductor makes contact in the clamping area gently. This prevents damage to the conductor and contact point which still have the same properties even after repeated clamping.

The tumbling barrel test is an impact test that simulates the fall of a test object from a height of 500 mm 50 times in a standardized rotating barrel. This test is carried out on a single terminal block. In the process, no defects that might impair further use of the terminal block may occur. This includes all damage that affects the tight fit on the DIN rail as well as chipping and fractures that affect the insulation or the air clearances and creepage distances. In the case of Phoenix Contact terminal blocks, this test also guarantees the tight fit of the assembled individual parts in the housing, given the sometimes-long transport distances of the packaged terminal blocks before installation.

In practice, tensile forces can affect the terminal point during wiring or operation. Therefore, terminal blocks must be wired correctly to offer a high degree of mechanical safety. To test the tensile load capacity of a terminal point, the terminal point must withstand a given tensile force based on the cross-section for over 60 seconds. This test is performed after the flexion test. Performing these two tests directly one after the other intensifies the requirements. The tensile force exerts stress on the conductor at the terminal point. The conductor must be held without damage. The AWG tensile force is based on the cross-section to be tested (see table). The test results for terminal blocks from Phoenix Contact are up to 150% above the required minimum values.

The mechanical strength of the terminal point is checked in a practical test. For this purpose, the terminal points of the terminal blocks must be repeatedly connected without loss of quality in the terminal connection. Therefore, solid conductors with the rated cross-section are used to connect and disconnect a terminal block five times as specified in the manufacturer’s information. Switching is done on the middle terminal block of a block of five. Before and after the test, the terminal blocks must pass a voltage-drop test. The terminal point must withstand repeated reconnection without sustaining noticeable damage. The voltage drop must not exceed 3.2 mV before the test. The voltage drop after the test must not exceed 1.5 times the value measured before the test. Terminal blocks from Phoenix Contact are suitable for repeated connection without any recognizable loss of quality. The number of possible connections can reach up to 5000 cycles, depending on the connection technology.

IEC 62262 describes a test procedure to determine a degree of protection (IK value) against mechanical strain. This degree of protection is mainly determined in connection with housings and boxes. In the test, a defined impact element (hammer) hits the horizontally mounted test object five times in succession at different points in a vertical drop with a precisely defined energy. The impact range of the impact element forms a semi-circle. The impact elements for the different degrees of severity are divided into six categories. The CLIPLINE complete connector housings for the Push-in COMBI series have a degree of protection of IK5.

The shock testing is used to test and document the resistance of a terminal connection to shocks that occur at irregular intervals (with varying energy content). In doing so, degrees of severity from DIN EN 50155 and IEC 61373 (international standard for railway applications) are used to simulate the load in rail traffic. For the definition of the shock, acceleration and duration are specified. IEC 60068-2-27 prescribes three positive and negative shocks on each of the three spatial axes (x, y, z). The simulated accelerations reach 50 m/s² with a shock duration of 30 ms. No damage may occur at the terminal connection that would impair further use. The contact behavior at the test objects is monitored during the test. When the German railway standard is applied, no contact interruptions >1 µs are permitted. Phoenix Contact terminal blocks achieve this shock resistance, making them also suitable for applications with strong
vibrations.

In process engineering, rapid changes in temperature often occur near process-related sources of heat and cold. This test verifies that the contact quality of the terminal points remains consistently high even in the case of rapid changes in temperature. For testing purposes, five terminal blocks are mounted on the support and wired to a conductor with the rated cross section. The structure is subjected to rapid temperature changes using a two-chamber method. The temperatures lie close to the upper and lower limit temperatures of the terminal block. This is generally a temperature range of -60°C to +100°C. The dwell time in each climatic chamber is 45 minutes, whereby the change takes place within a few seconds. This change is performed for 100 cycles. The requirements are met if, after the test, the single parts are undamaged and their further use is guaranteed.

In many applications, terminal blocks are exposed to vibrations and shocks. This interference is not always harmonic, regular, or consistent in frequency. Such vibrations can be caused by mounting in means of transport, such as rail vehicles, for example. These loads also occur in production machines or in mining technology. Railway applications are leading the way here in defining the degree of severity for vibration testing. DIN EN 50155 states that if not established otherwise, the requirements of EN 61373, Category 1, Class B apply. This results in the following parameters (see table). For a practical simulation of the vibration stress, the test objects are subjected to broadband noise-induced vibrations in the laboratory. This means that realistic accelerations are generated at the terminal block and the connected conductor. For the signal mix to be real, a certain distribution of accelerations and amplitudes must be guaranteed. During the category 1 B test, the objects are exposed to a frequency range of 5 Hz to 150 Hz. The RMS value of the acceleration is up to 5.72 m/s². The test objects are tested for 5 hours on each of the three axes (X, Y, Z). In addition to the vibrations, the electrical contact is monitored during the test for interruptions. During this, no damage may occur at the terminal blocks that would impair their further use. In addition, no contact interruptions >1 μs are permitted during the test. The contact resistance is measured before and after the test. The resistance must be ≤1.5 times the initial value. Terminal blocks of all connection technologies from Phoenix Contact achieve this requirement from the standard without impermissible contact interruption. They are therefore well-suited for demanding applications in which a reliable functioning of the terminal connection has to be ensured when subjected to vibrations.

This test demonstrates the vibration resistance of a terminal connection subjected to continuous vibrations as they can be caused by rotating masses, for example. Such vibrations occur for example in power plant turbines and generators, in wind turbine generators, and in motors or drives. Harmonic, sinusoidal vibrations are applied to the test object on the vibration test system (vibrating table) to simulate even, vibrating forces. The test runs through a frequency range of 5 Hz to 150 Hz and then back to 5 Hz per cycle. In the process, the amplitude of the oscillation on the vibrating table is kept constant up to 25 Hz. However, above this value, the acceleration of the component remains constant. The RMS value of the acceleration is up to 50 m/s². The frequency changes with one octave per minute, i.e., it doubles or halves its frequency every 60 s. The test objects are tested for 2 hours on each of the three axes (X, Y, Z). During this, no damage may occur at the terminal blocks that would impair their further use. In addition, no contact interruptions (>1 μs) are permitted during the test. The contact resistance is measured before and after the test. The resistance must be ≤1.5 times the initial value. All connection technologies achieve this requirement from the standard without impermissible contact interruption. They are therefore well-suited for demanding applications in which a reliable functioning of the terminal connection has to be ensured when subjected to vibrations.