In the field of electrical installations, fire safety is of paramount importance. Fire resistant cables play a vital role in preventing the spread of fire and ensuring the integrity of electrical circuits even in extreme conditions. The BS 6387 standard provides specifications and testing methods for fire resistant cables, specifically focusing on their resistance to fire alone. This article explores the apparatus for the test to fire alone, fire-resistance testing for electric cables, and the significance of BS 6387 2013 in ensuring fire safety.
Fire resistant cables are designed to maintain operational integrity even when exposed to high temperatures and flames. These cables possess enhanced insulation and sheathing materials that delay the spread of fire, limit smoke emission, and minimize toxic gas release. They are widely used in critical applications such as emergency lighting, firefighting equipment, alarm systems, and power supply circuits that need to remain functional during a fire incident.
| The cable is clamped laterally by clamps at both ends of the cable sheath. The middle part of the cable is fixed by two metal rings (300mm apart), which are grounded with other metal parts of the device. | Cable Support System | Resistance to Fire Alone |
| See the figure below for the cable support device. For unarmored cables with a diameter less than 10mm, or other cables that undergo significant displacement during the test, there are 3 metal rings, each fixed at about 150mm from the original metal ring. | ||
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| The test is conducted by passing current through all cores of the cable, a three-phase star-connected transformer or three single-phase transformers (or one single-phase transformer if the test is a single-core cable) and has sufficient capacity to maintain the test voltage The maximum allowable leakage current is 3A. | Continuous Detection Device | |
| 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. | ||
| The heat is provided by a 610 mm long tube gas burner with a forced supply of methane and a dense flame. | Heat (Fire) Source | |
| Temperature Measurement: An armored thermometer with a diameter of 2mm is placed near the air inlet and 75mm parallel to the burner. | ||
| Test Flame Temperature and Ttime: (Refer to BS6387 Combustion
Grade) A 650℃ ± 40 °C ~3 hours B 750℃ ± 40 °C ~3 hours C 950℃ ± 40 °C ~3 hours S 950℃ ± 40 °C ~20 minutes |
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| Test Specimen: The sample is a section of the finished product, not less than 1200mm, with 100mm of sheath and covering removed from both ends. The conductors at both ends of the cable shall be electrically connected. | ||
| Power Voltage for Test：200 ~ 1000V Adjustable | ||
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| Fire Tests｜Cables must undergo meticulous design, manufacturing, and testing processes. Manufacturing includes several tests, which may be attended by customers or third-party inspectors, ensuring the quality of the cables. The following are the key tests conducted to assess cable performance in fire scenarios. | |||
| Test Method of BS EN 50200 | BS EN 50200 Annex E (Standard Cable – BS 5839-1:2017 – Clause 26.2d) | BS 8434-2 (Enhanced Cable – BS 5839-1:2017 – Clause 26.2e) | Test Method of BS 6387 |
| Test Method of IEC 60331 | BS EN 60332-3, IEC 60332-3 | BS EN 60332-1, IEC 60332-1 BS EN 60332-2, IEC 60332-2 for small diameter cables | |
Resistance to fire alone refers to a cable’s ability to maintain circuit integrity in the event of a fire without external influences such as water or mechanical damage. The BS 6387 standard provides guidelines for fire-resistance testing of electric cables and is widely recognized in the industry. The standard incorporates various tests, including the direct application of fire, to assess the performance of cables under fire conditions.
| The apparatus used for the test to fire alone is critical in determining the cable’s resistance to fire. It simulates real-life fire scenarios to evaluate the cable’s performance and ensure compliance with safety standards. | Apparatus for the Test to Fire Alone: |
| The test apparatus typically includes a furnace, test section, measurement instruments, and control systems. During the test, the cable is subjected to high temperatures and direct exposure to flames to assess its ability to maintain circuit integrity. | |
| Fire-resistance testing for electric cables involves subjecting the cable samples to challenging conditions to evaluate their performance during a fire incident. | Fire-resistance Testing for Electric Cables: |
| The tests help identify the critical parameters such as flame spread, smoke emission, insulation integrity, and circuit continuity. | |
| They assess various cable properties, including fire retardant materials, insulation thickness, sheathing materials, and overall construction. |
| 650°C
for 3 hours → A Level 750°C for 3 hours → B Level 950°C for 3 hours → C Level 950°C for 3 minutes (short duration) → S Level |
Resistance to Fire Alone | BS 6387 Flame Retardant Grade: BS6387 requires passing horizontal combustion test, water spray test and mechanical impact shock combustion test. |
| Class A means that it can burn for 3 hours with a voltage of 300 volts applied at 650℃ without breakdown; | ||
| Class B means that it can burn for 3 hours with a voltage level of 300 volts applied at 750℃ without breakdown; | ||
| Class C means that it can burn for 3 hours with a voltage level of 300 volts applied at 950°C without breakdown; | ||
| Class S means that it can burn at 950°C for 3 minutes at a voltage level of 300 volts without breakdown. | ||
| W Level: Resistance to fire with water Exposed to fire @ 650°C for 15 mins then exposed to fire @ 650°C with water for another 15 mins. | Resistance to Fire with Water | |
| Exposed to
fire @ 650°C for 15 mins then exposed to fire @ 650°C with mechanical shock
for 15 mins → X Level Exposed to fire @ 750°C for 15 mins then exposed to fire @ 750°C with mechanical shock for 15 mins → Y Level Exposed to fire @ 950°C for 15 mins then exposed to fire @ 950°C with mechanical shock for 15 mins → Z Level |
Resistance to Fire With Mechanical Shock | |
| Grade X means that a voltage of 300 volts is applied at 650°C while burning, and mechanical shock vibration is carried out every 30 seconds for 15 minutes without breakdown. | ||
| Level Y means that it will not break down when a voltage of 300 volts is applied at 750°C while burning and subjected to mechanical shock and vibration every 30 seconds. | ||
| Level Z means that it will not break down when a voltage of 300 volts is applied at 950°C while burning and subjected to mechanical shock and vibration every 30 seconds. | ||
| The highest level model required by BS 6387 is CWZ. |
| BS 6387:2013 is a British Standard that provides detailed specifications for the performance of cables with improved fire characteristics. It outlines the test methods and requirements for cables to be classified as fire resistant. | BS 6387 2013 and Its Significance: |
| The standard covers various criteria, including flame propagation, circuit integrity, insulation resistance, and mechanical shock resistance. Compliance with BS 6387 ensures that fire resistant cables meet the necessary safety standards and regulations. | |
| Fire retardant cables are specifically designed to resist the spread of fire and minimize the release of toxic gases, smoke, and heat. In addition to BS 6387, other important standards governing fire retardant cables include BS EN 50200 and IEC 60331-1. | Fire Retardant Cables and Related Standards: |
| BS EN 50200 focuses on fire resistance testing of cables for emergency systems, while IEC 60331-1 specifies the test methods for cables in combination with fire conditions. |
Resistance to fire alone is a crucial aspect of fire safety, particularly for fire resistant cables. The BS 6387 standard provides the necessary guidelines and testing methods to evaluate the performance of these cables during a fire incident. The apparatus used for the test to fire alone simulates real-life fire scenarios, enabling accurate assessment of cable behavior. Compliance with standards such as BS 6387, BS EN 50200, and IEC 60331-1 ensures that fire resistant cables meet the necessary safety requirements.