Fire resistant (FR) cables play a crucial role in ensuring safety in various industrial sectors. These specialized cables are designed to withstand extreme conditions, including exposure to fire and mechanical shock. In this article, we will explore the concept of resistance to fire with mechanical shock and the importance of conducting tests to ensure the reliability and efficiency of FR cables.
We will also discuss the necessary apparatus and equipment for resistance to fire with mechanical shock testing, relevant standards such as BS 6387 and IEC 60331, and the significance of fire alarm cables in fire safety systems. Resistance to fire with mechanical shock refers to the ability of FR cables to withstand the combined effects of fire and physical impact.
Apparatus for Resistance to Fire with Mechanical Shock Testing : To evaluate the resistance of FR cables to fire and mechanical shock, specific apparatus is utilized. This includes test chambers, shock devices, and water jet equipment. The test chamber provides a controlled environment for simulating fire conditions, while the shock device delivers precise mechanical impacts to the cables. Additionally, the water jet equipment replicates the use of water for firefighting purposes, assessing the cables’ resistance to water pressure and ensuring their continued performance.
| Fix the components in their corresponding positions on the slotted frame. | Resistance to Fire with Mechanical Shock | ||
| The cable is fixed to a vertical wall and fixed to the steel plate with heat-resistant and non-combustible material. | |||
| The transformer is connected to the fuse and light to show that the circuit is continuous. | |||
| The wall is made of heat-resistant, flame-retardant material and is fixed to two horizontal steel beams, one at the top and the other at the bottom of the slab. | Walls and Its Installation | ||
| The board is approximately 900 mm long, 300 mm wide and 9 mm thick, and the total weight of the wall (i.e. board plus supporting frame) is 10 ± 2 kg. | |||
| Each steel beam is a square steel tube approximately 1m long and 25mm long. | |||
| If filler material is required, it needs to be placed inside the steel beam. | |||
| The upper steel beam must be fastened to the slab so that its upper surface is flush with the upper edge of the slab. | |||
| Each steel beam and plate has a horizontal hole at its outer edge, the precise location of which is determined by the specific support padding and support frame requirements. | |||
| The wall is bonded to the frame with 4 rubber bushings approximately 32mm in diameter and 20mm thick. | |||
| During the test, current is allowed to pass through all cores of the cable, and the three single-phase transformers have sufficient capacity to maintain the test voltage reached. | Continuous Detection Device | ||
| The maximum allowable leakage current is 3A. | |||
| Connect a lamp to each core wire at the other end of the cable and load it with a current of close to 0.25A at the rated voltage of the cable. | |||
| A strip burner with a length of 400mm can burn up to 400mm cable samples. | Heat (Fire) | Heat (Fire) Source | |
| The burner assembly can be adjusted to provide a bright flame at a temperature of 650 ± 40 °C | |||
| An armored thermometer with a diameter of 2mm. The thermometer passes through the wall and is 8mm to 10mm away from the wall. | Temperature Measurement: | ||
| The temperature is measured using the following procedure: A thermometer is tied to one end of a low carbon steel rod with a diameter of 3mm±5% and a length of 300mm to enable it to measure the temperature of the rod. Hold the rod close to the flame so that it is 40mm to 50mm away from the flame. At this temperature, when the flame temperature is 950°C, the temperature of the steel rod can reach 400°C in 10s to 20s. When the flame temperature is 650°C, the temperature of the rod can reach 400°C in 20s to 40s. |
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| The test temperature needs to be selected from the
following: X 650 ± 40°C Y 750 ± 40°C Z 950 ± 40°C |
Test Flame Temperature and Time: | ||
| The vibration device consists of a low carbon steel rod (diameter 25mm± 5%, length 600mm± 5%) | Shock Impact Device | ||
| The longitudinal tangent line of the rod is parallel to the wall and 200mm higher than the top of the wall. | |||
| An axis divides it into two parts, 200mm and 400mm, with the long part facing the wall. | |||
| Drop it from a parallel position to the middle position of the wall from 60°C at intervals of 30±2S, see the figure below. | |||
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| The test specimen is a section of the finished cable and is not less than 1200mm, with 100mm of sheath and covering removed from both ends. | Test Specimen | ||
| The conductors at both ends of the cable should be suitably prepared for electrical connections and in accordance with the manufacturer’s recommendations. | |||
| The cable needs to be bent in the middle into two nearly equal-length, parallel sections. | |||
| The diameter of the bent part is 6 D, where D represents the outer diameter of the cable. | |||
| Make the cable into a Z-shape, with the two ends fixed at a distance of 13 D horizontally, as shown in the figure below. | |||
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| The cables need to be fixed to the wall with copper clips, and the installation of special cables needs to be referred to the manufacturer. | |||
| The clips need to be fixed on the two bent parts of the cable, with the middle part of the bend being vertical. | |||
| In the section where the cable becomes horizontal, the distance between adjacent clips is equal to approximately 150mm to 200mm | |||
| 200 ~ 1000V Adjustable | Power Voltage for Test | ||
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In real-life scenarios, such as industrial fires or explosions, cables may be subjected to not only high temperatures but also mechanical stresses caused by falling debris, collapsing structures, or water jets from firefighting efforts. It is essential to ensure that FR cables can maintain their functionality and structural integrity under such adverse conditions to enable the safe evacuation of personnel, protection of assets, and continuity of critical operations.
| The equipment used for conducting fire resistance tests with shock devices and water jets is designed to mimic real-world scenarios. It should incorporate features such as temperature control, shock delivery systems, and water jet mechanisms. | Equipment for Fire Resistance Test with Shock Device and Water Jet: |
| The integration of these components allows for a comprehensive evaluation of FR cables’ performance under simultaneous fire exposure and mechanical shock. | |
| The test for resistance to fire with mechanical shock involves subjecting FR cables to controlled fire conditions while applying mechanical shocks. The cables are installed in the test chamber following specific configurations, with proper consideration of their application and installation requirements. | Test for Resistance to Fire with Mechanical Shock: |
| The test assesses various parameters such as cable insulation integrity, electrical continuity, and transmission capabilities under severe fire conditions and mechanical stress. | |
| Standards such as BS 6387 and IEC 60331 provide guidelines for testing the resistance to fire with mechanical shock in FR cables. BS 6387 evaluates cables’ performance under fire conditions, including direct flame exposure, impact from falling debris, and water spray. | Importance of Compliance with Standards: |
| IEC 60331 assesses cables’ ability to maintain circuit integrity and functionality during fire situations to ensure the continuous operation of critical systems. |
The resistance to fire with mechanical shock is a critical aspect of ensuring the reliability and efficiency of fire resistant (FR) cables. Through appropriate testing methods and compliance with relevant standards, FR cables can demonstrate their ability to withstand fire conditions and mechanical stresses.
This article has highlighted the importance of conducting resistance to fire with mechanical shock tests, the necessary apparatus and equipment, and the significance of fire alarm cables in fire safety systems. By adhering to these principles, industries can enhance their fire safety measures and protect lives and assets from the devastating effects of fire.