Fire resistant cable

Fire resistant cable refers to a cable that can maintain safe operation for a certain period of time under the condition of flame combustion. The national standard GB12666.6 (equivalent to IEC331) in our country divides the fire resistance test into two levels: A and B. The flame temperature is 950~1000 ℃, and the continuous fire supply time is 90 minutes. The B level is 750~800 ℃, and the continuous fire supply time is 90 minutes. During the entire test period, the sample should withstand the rated voltage value specified by the product.

Fire resistant cableTerms of Use

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1. AC rated voltage: U./U (V series: 600/1000V, K series: 450/750V, B series: 450/750V).

2. Maximum long-term operating temperature of the cable

3. Low ambient temperature:

(1) Flame retardant polyvinyl chloride insulation and sheath: fixed installation at -40 ℃; Non fixed installation -15 ℃;

(2) Fluoroplastic insulation and sheath: fixed installation -60 ℃; Non fixed installation -20 ℃;

4. The safe laying temperature of cables should not be lower than 0 ℃.

5. Fire resistance characteristics:

Compliant with IEC331 and GB12666.6 regulations

750 ℃ flame temperature 950 ℃ -1000 ℃ flame temperature 750 ℃ -800 ℃

Burning time 3h, burning time 90min, burning time 90min

Cooling time 21 hours, additional voltage, rated voltage, additional voltage, rated voltage

Additional voltage, rated voltage, additional current 3A, additional current 3A

Additional current 3A Class A Class B

6. Recommended allowable bending radius for laying: Non armored and braided shielded cables should not be less than 6 times the outer diameter of the cable;

Steel tape armored cables should not be less than 12 times the outer diameter of the cable;

Insulated and sheathed cables should not be less than 8 times the outer diameter of the cable.

Common models

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Model meaning

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1. Model composition

2. Combustion Characteristics Code Table

classification

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In China, ordinary fire-resistant cables are divided into Class A and Class B: Class B cables can withstand combustion for at least 90 minutes in flames between 750 ℃ and 800 ℃ and at rated voltage without being broken down. On the basis of improving the manufacturing process of the refractory layer and increasing the refractory layer, Class A fire-resistant cables have been developed, which can withstand combustion for at least 90 minutes in flames at 950 ℃ to 1000 ℃ and rated voltage without being broken down (i.e. 3A fuses do not melt). The fire resistance performance of Class A fire-resistant cables is superior to that of Class B. In addition, mineral insulated cables are a type of fire-resistant cable with better neutral performance. They are processed from copper core, copper sheath, and magnesium oxide insulation material, abbreviated as MI (mineral insulated cables) cables. This cable * is composed of inorganic materials forming a refractory layer, while the refractory layer of ordinary fire-resistant cables is composed of a composite of inorganic materials and general organic materials. Therefore, the fire-resistant performance of MI cables is better than that of ordinary fire-resistant cables and will not decompose and produce corrosive gases due to combustion. MI cables have good fire resistance and can operate at high temperatures of 250 ℃ for a long time. They are also explosion-proof, corrosion-resistant, have a large current carrying capacity, radiation resistance, high mechanical strength, small size, light weight, long service life, and smoke-free. However, due to its high price, complex process, and difficult construction, this type of cable with good fire resistance performance can be used in oil irrigation areas, important wooden public buildings, high-temperature places, and other places with high fire resistance requirements and acceptable economic viability.

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Based on the specific characteristics of fire-resistant cables, designers should pay attention to the following issues when designing and selecting:

(1) When fire-resistant cables are used in cable tunnels with dense cables, cable interlayers, or in flammable places such as near oil pipes and oil depots, Class A fire-resistant cables should be selected first. In addition to the above situations and when the number of cable configurations is small, Class B fire-resistant cables can be used.

(2) Fire resistant cables are mostly used as power supply circuits for emergency power sources, requiring normal operation during a fire. Due to the rapid increase in ambient temperature during a fire and the decrease in voltage drop, for circuits with long power supply lines and strict limits on allowable voltage drop, the cross-section of fire-resistant cables should be enlarged by at least one level.

(3) Fire resistant cables cannot be used as high-temperature resistant cables.

(4) To reduce the probability of failure in fire accidents, the number of joints should be minimized as much as possible during installation to ensure that the circuit can work normally in a fire. If branch wiring is required, fire protection measures should be taken for the joints.

The difference between flame-retardant wires and cables and fire-resistant wires and cables

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Its flame retardancy refers to the ability to block and delay the spread and extension of flames along wires and cables in the event of a fire accident, minimizing the expansion of the fire range. This type of cable has the characteristic of self extinguishing after ignition. Generally speaking, it can be understood that when the wire and cable product catches fire due to its own ignition or external heat sources, after the fire source subsides, the wire and cable product will no longer continue to burn, or the burning time will be very short. In the category of wires and cables, the symbol - ZR is commonly used to indicate this type.

Meanwhile, flame-retardant wires and cables are divided into halogen-free flame-retardant wires and cables and halogen-free flame-retardant wires and cables. Compared to halogenated flame-retardant wires and cables, halogen-free has the advantages of low toxicity and low smoke. The product model is represented as - WDZR.

Fire resistant wires and cables refer to Shandong wire and cable manufacturers' products that can maintain normal operation for a certain period of time, maintain the integrity of wire and cable lines, and ensure the normal operation of line equipment even when external flames are still burning in the event of a wire and cable fire accident.

Fire resistant wires and cables can be divided into two levels according to national standards:. Usually represented as NHA and NHB categories. The determination of whether a wire and cable product belongs to fire-resistant wire and cable is not related to whether the wire and cable product itself has self extinguishing properties. The greatest function of flame-retardant wires and cables is the inherent flame retardancy of the wire and cable products. Fire resistant wires and cables can typically maintain normal operation for at least 180 minutes at flame temperatures ranging from 750 to 800 ℃.

There is also a special type of fire-resistant cable called fire-resistant wire cable. It is made of seamless copper tube as the sheath and magnesium oxide as the insulation material. Due to the special nature of its materials, fire-resistant wires and cables do not burn or spread flames. Experiments have shown that fire-resistant wires and cables can still operate normally for 2 hours at 800-900 ℃, and can continue to operate normally for 30 minutes at 1000 ℃[3].