Material tests for terminal blocks

From the point of view of long lifecycles of the terminal blocks, the aging behavior also plays an important role. In this test, the contact quality is verified by means of simulated aging. To simulate several years of use, five terminal blocks are mounted horizontally on a rail and connected in series using conductors with the rated cross-section. Conductors with a minimum length of 300 mm are connected and the voltage drop is measured at every terminal block. The minimum temperature in the climate cabinet is set to +20°C. In contrast, the upper temperature is set so that the maximum permissible operating temperature (max. +120 C) of the test object is reached during the 10-minute pause phase. During the heating phase and the pause phase at the maximum temperature, the rated current flows. As a result, the maximum permissible operating temperature of the test object (maximum +130°C) is reached. This is followed by the cooling phase. The voltage drop is always measured after 24 cycles in the cooled-down state (approximately +20°C). The test consists of a total of 192 cycles. The voltage drop must not exceed 3.2 mV initially. During or after testing, it must not exceed 4.8 mV or 1.5 times the value measured after the 24th cycle. Terminal blocks from Phoenix Contact are designed for extreme durability even under difficult temperature conditions. Plastic as well as metal parts provide sufficient safety reserves.

EN 45545-2 has replaced the national fire protection standards for rail vehicles since March 2013. The current version of EN 45545-:2013+A1:2015 presents the demands placed on the fire behavior of materials and components. To qualify plastics for certain operating and design classes of rail vehicles, the standard describes testing methods for determining hazard levels (HL). In this case, HL3 corresponds to the highest requirements. The following tests are performed in order to qualify the plastics for electrical engineering applications:

• Oxygen index according to DIN EN ISO 4589-2
• Development of smoke gas in accordance with EN ISO 5659-2 (25 kW/m²)
• Toxicity of smoke gas NF X70-100-2 (600°C)
• Vertical small flames test in accordance with EN 60695-11-10
  The unreinforced polyamides used in Phoenix Contact terminal blocks with flammability rating UL 94 V0 meet the highest demands. They meet the most stringent requirement of flammability rating HL3 in accordance with the tests described in the requirement sets R22, R23, R24, and R26.

The UL 94 standard describes inflammability tests that have gained particular importance in the field of electrical engineering. Fire behavior is the main focus. Items are classified in accordance with either UL 94 HB (Horizontal Burn) or UL 94 V (Vertical Burn). The test setup is such that the UL-94-V0/1/2 classifications are stricter than the UL-94HB classification.

UL 94 V0/1/2
After conditioning, the test bar is vertically clamped and flame-treated several times for 10 seconds at a time. Between the flame treatments, the time until the test bar is extinguished is measured. Afterwards, the afterburning times and the drip behavior are evaluated. The plastic used for Phoenix Contact terminal blocks satisfies the higher-grade criteria for classification as a V0 material.

The fire load is defined as the amount of energy released over a particular area during burning. The fire load value is usually expressed in MJ/m². The value is calculated based on the calorific value of a substance and the combustion factor (DIN 18230-1). The higher the calorific value and the presence of a substance, the greater the amount of energy released during burning. It follows that the possible fire load value is also higher. This affects all installed components in the application to be considered. The calorific values of polyamides such as PA 6.6 are relatively high (for comparison: the calorific value of fuel oil is approx. 44 MJ/kg). For this reason, the calorific values of terminal blocks are also increasingly included in the fire load determination. Calorific values of the plastics used by Phoenix Contact in accordance with DIN 51900-2 and ASTM E 1354 can be found in the following table. To calculate the fire load of individual components, the calorific value of each polyamide must be multiplied by the weight of the part and the number of items installed. Documentation of the heat emission takes place in the cone calorimeter in accordance with ISO 5660-1 for the plastic materials.

In the event of overload, conductive metal parts of the terminal block or connected conductors can heat up considerably. This additional heat also affects the plastic housing. To simulate this source of danger for electrical engineering components, a glow wire is heated to a particular temperature (+550°C, +650°C, +750°C, +850°C, or +960°C). As shown in the figure, the wire is then pressed onto the thinnest point of the test object housing at a right angle with a force of 1 N.
The test is considered passed for the following results:

• When no flame or glowing process occurs during the test
• When the flames or glowing processes are extinguished within 30 seconds of the glow wire being removed
• When the tracing paper beneath the glow wire does not ignite due to any drops of burning substances falling down

The polyamides used by Phoenix Contact as housing materials all fulfill the requirement of the glow-wire test at +960°C (highest temperature level).

In the associated test, an increased thermal load on the terminal block is simulated over a longer period of time. For this purpose, the behavior of plastics at constantly higher temperatures is considered with respect to the tensile strength (mechanical properties). The standard requires at least three, but preferably four, different temperature measurement series to be performed on a test piece. The tensile strength is measured over 500 h to 5,000 hours depending on the specification and the result is extrapolated to 10,000 hours (HCI) and 20,000 h (TI). After these 20,000 hours, you can determine the temperature at which the tensile strength decreased by half. IEC 60216 specifies the TI as a temperature index that permits conclusions to be made about the mechanical service life of plastics under thermal loads.
TI values according to UL 94 V2: +105°C
TI values according to UL 94 V0: +125°C

Humidity depends on temperature and atmospheric pressure. The warmer the air, the more humidity it can hold. 100% humidity reflects the maximum saturation of water vapor in the air at the respective temperature. The test described here includes one or more temperature cycles at high humidity (>90% ... 100% at 40°C or 55°C). Terminal housings are usually made of polyamide. These plastics absorb water proportionally and thus also change their elasticity. Polyamides PA6 and PA66 can absorb moisture content above eight percent by weight when stored in water at around +80°C for several days. Moisture absorption is also associated with a dimensional change due to “swelling”. Under actual climatic conditions, polyamide absorbs approx. 2 ... 4% moisture with a change in length of 0.6 ... 0.8%. After the terminal blocks pass through the test cycles, their proper tight fit, operability, and function must be ensured by a dielectric test and by testing the tight fit of the conductor.
At test level A, the terminal blocks are subjected to two cycles at +40°C.
For test level B, the terminal blocks are subjected to one cycle at +55°C.

The following test with dry heat is used to evaluate the suitability of a component for operation, storage, or transport at a high temperature.

In the process, a distinction is made between heat-emitting and non-heat-emitting test objects. Terminal blocks belong to the latter category, and are therefore subjected to test scenario Test Bb (with gradual temperature change). The degrees of severity are defined by the strain temperature and the strain duration. In the case of terminal blocks, the proper tight fit and function must be subsequently ensured through a dielectric test and testing of the tight fit of the conductor.

The degree of severity for Phoenix Contact terminal blocks is at +85°C und 168 h.

The key role of the metal parts of electrical connections becomes particularly apparent in aggressive environments. Corrosion-free contact areas are a prerequisite for low-resistance and therefore high-performance connections. This test procedure describes a corrosion test in a condensation climate with an atmosphere that contains sulfur dioxide. Acidic compounds <pH 7 form during the test and attack the metal surfaces. Two liters of distilled water and one liter of SO2 gas are introduced into the test chamber. At a test temperature of +40°C, sulfurous acid (H2SO3) forms during the test. After eight hours of testing, the test objects dry for 16 hours with the door open. After the end of the test, the test objects are visually inspected and the contact resistance is measured in order to show the influence of this corrosion test on the contact point in more detail. Phoenix Contact terminal blocks create high-quality, gas-tight connections that cannot be impaired even by aggressive substances.

Particularly in shipbuilding and offshore applications, technical components have to function continuously in corrosive atmospheres. The salt content of the air combined with the increased humidity places high demands on the metal parts used. The impact of the climate at sea can be simulated on the basis of the above standard. The resistance of the metal parts and the corrosion protection is tested using salt spray in corrosive atmospheres. The test objects are placed in the test chamber and subjected to a fine spray of 5% sodium chloride solution (NaCl: pH value 6.5–7.2) at a temperature of +35°C for a period of 96 hours. To better evaluate the influence on the contact points, there is a visual check of the test objects and an electrical test after the end of the test. Phoenix Contact terminal blocks with all connection technologies create gas-tight connections, which also protect the contact points from corrosion under extreme climatic conditions.

Humidity and contamination facilitate the formation of creepage on the plastic surface. Formation of creepage distances refers to the occurrence of conductive connections between neighboring potentials. Consideration is given to the dependence of the potentials on their voltage differences under electrolytic influences. The CTI value of a plastic indicates the extent to which this formation of creepage is prevented. Two platinum electrodes are placed 4 mm apart on a test piece measuring 20 mm x 20 mm x 3 mm. A test voltage in accordance with standard specifications is applied to both electrodes. An electrolyte solution is then dripped onto the electrodes by a test apparatus at a rate of one drop every 30 seconds. The test evaluates the maximum voltage value without a current flow >0.5 A. The plastics used by Phoenix Contact are classified in the highest test voltage category with a CTI value of 600.

As far as the use of terminal blocks is concerned, fire behavior when in direct contact with a source of ignition is a major criterion. Such sources of ignition could be electric arcs along a creepage distance, for example. Terminal blocks must not aid or accelerate fires and the plastics must have self-extinguishing properties. This fire test simulates the behavior of the components with an external source of ignition acting on them directly from outside. In the test procedure, a naked flame fed with butane gas is held at an edge or surface of the test object at an angle of 45° for 10 seconds (see figure). The behavior of the test object without a source of ignition is then
observed. The test is considered be passed when the flames or glowing processes are extinguished within 30 seconds of the flame being removed and when the tracing paper beneath the test object is not ignited by falling drops of burning substances. All terminal blocks from Phoenix Contact pass the needle flame test due to the high-grade plastics used and their structural design.

To evaluate the surface inflammability and the flame spread of plastics, a “flame spread index” is devised in accordance with ASTM E 162. For this purpose, a sample is irradiated with a heat source and also ignited with a naked flame. During the duration of the test, the time in which the flame front reaches two measuring points that are opposite each other is determined. The product of this flame propagation time and a calculated heat development factor yields the flame spread index. The drip behavior of the plastic is also observed and evaluated during the test. In the United States, the maximum flame spread index is 35. Terminal blocks from Phoenix Contact achieve a value of 5 and produce non-burning droplets. The value therefore lies well below the approved maximum values of the Federal Railroad Administration (FRA) of the US Department of Transportation.

EN ISO 5659-2 describes a method for evaluating the smoke development of a substance in the event of a fire under additional radiant heat. The test is performed on a total of six test pieces, but individually in an airtight lockable test chamber. The test pieces must be square (75 mm x 75 mm) with a level surface and no thicker than 25 mm. They are wrapped with aluminum foil in such a way that only the top side is left free of a strain area of 65 mm x 65 mm. For the test, the test piece is fixed horizontally in a bracket and exposed on its surface to an irradiation of 25 kW/m² for 10 minutes. The test occurs on three samples with and three samples without a pilot flame. The optical smoke density is measured via a photometric process. First, the value changes of the focused light beam hitting a photo-sensor are measured in mV. (full light quantity = 100%, darkness = 0%)
The values obtained are converted using the following formula and expressed as smoke density:
Dsmax = 132 * log 10 / 100 Tmin

Picture description: 1. Optical measuring system 2. Pressure regulator 3. Light path 4. Upper air inlet opening (upper area) and lower air outlet opening, connected to the exhaust fan (at the bottom) 5. Chamber 6. Cone heating device 7. Window 8. Pilot flame burner 9. Test piece in holder 10. Weighing device 11. Lockable door 12. Optical window 13. Light source

NF DIN EN ISO 4589-2 describes a test to evaluate the fire behavior of plastics based on an oxygen index (OI). For plastics, such as those used in the electrical industry, a plate size with a length of 70 ... 150 mm, a width of 6.5 mm (±0.5 mm), and a thickness of 3 mm (±0.25 mm) should be used for testing. This plate is mounted vertically in a glass cylinder, surrounded by a mixture of oxygen and nitrogen, and lit at the top edge with a propane gas flame. Then, the combustion behavior at different oxygen contents of the circulating gas is analyzed. Ignition consists of up to 30 s of exposure to flame followed by a 5 s pause. The exposure to flame is repeated in 5 second intervals until the test piece burns on the surface. The goal is a 180 s-long burn duration after removing the propane gas flame. No more than 50 mm, measured from the ignited edge, should have dripped or melted away while burning. Flame interruptions ≤1 s are permitted. If the flame goes out after 180 s have passed, the measurement is rated as “O” and the oxygen content is increased for the next sequence. If the flame is still there after the 180 s have passed, the measurement is rated as “X” and the oxygen content is reduced for the next sequence. On multiple test pieces, an accuracy of the oxygen threshold (at which the item is still burning) of ≤1% to “O” sequences is determined. This is later used to calculate the oxygen index OI.

1. Chimney
2. Chimney vent
3. Test piece bracket
4. Wire mesh shielding
5. Diffusor and a mixing chamber
6. Any temperature measuring device
7. Tube
8. Test piece
9. Oxygen/nitrogen mixture
10. Source of ignition

EN 60695-11-10 is used to evaluate the fire behavior. The material is ignited with a standardized 50 W needle flame. A rectangular, bar-shaped test object must be created for this purpose beforehand. This test object must be 125 mm x 13 mm x optionally 0.1 ... 12 mm thick. In test method “A”, three test bars are needed. During the test, each bar is fixed horizontally and the linear firing rate is measured as the evaluation. To do so, two marks are attached at 25 mm and 100 mm. Depending on the burnup, the classification is “HB // HB 40 // HB 75 // or, if the 100 mm mark is exceeded, with

v= L/t * 60s/min

v = rate of fire
L = length of damage
t = time

Five test bars are needed in test method “B”, where each bar is suspended vertically at one end and the free end is ignited with a test flame for 10 s. There is a cotton pad under the test object. Then the afterburning time t1 is determined. This is immediately followed by a second flame exposure of 10 s with measurement of the afterburning time t2 and the afterglow time t3. In the process, no burning drops may fall off and ignite the pad. The measured values for the evaluation are calculated as follows:

tf = (t1.1 +t2.1)(t1.2 +t2.2)(t1.3 +t2.3)(t1.4 +t2.4)(t1.5 +t2.5)