Basic knowledge of fireproof cables

1 Introduction Flame proof wire and cable is a general term for wire and cable with fire resistance. It is usually divided into flame retardant wire and cable and fire-resistant wire and cable. Starting from fire safety and firefighting, more and more requirements are placed on the fire performance of wire and cable, such as:

Flame retardancy - retards and retards the spread of flames along wires and cables so that the fire does not expand.

Fire resistance - Maintains operation for a certain period of time in the event of a flame, ie, maintains circuit integrity.

Free halogen—The material that makes up the wire and cable is halogen-free, and its combustion products are less corrosive.

Low-halogen—The material that makes up the wire and cable may contain halogen, but the content is low.

Low smoke - less smoke generated when the wire and cable are burned, ie higher light transmittance.

LOW toxicity - The gas generated when burning wire and cable materials is less toxic.

The research and development of fire-retardant and fire-resistant wires and cables in China began in 1982. After five years, that is, in 1987, many cable manufacturers have been put into production and accepted by users. In view of the confusion about the naming and type of combustion characteristics at the time, the author proposes the burning characteristics of the wire and cable corresponding to the combustion test method to classify the fire-resistant wire and cable, and use the first letter of Hanyu Pinyin as the prefix of the corresponding common wire and cable model. . Among them, the flame-retardant wire and cable model ZR and the fire-resistant wire and cable model NH have been used up to now.

With the many new developments in the research and development of fire-resistant wire and cable, the existing models are no longer adequate. In addition, more and more manufacturers are engaged in the production of enterprise standards, and the need for each type of model will cause new confusion. The most prominent performance is that the wire and cable have the same burning characteristics, but their names and models are different. The industry and users strongly demand that this situation be changed and hope to unify the model. For this reason, this article proposes the method of preparation of the model of fire-resistant wire and cable for the future preparation of corporate standards or industry standards.

2 Principles for the preparation of fire-resistant wire and cable models (1) One model corresponds to one combustion characteristic. There are corresponding test methods and specific indicators that can be evaluated and expressed in the first letter of Hanyu Pinyin.

(2) The model is prefixed with the ordinary wire and cable model.

(3) The inherent combustion characteristics of ordinary wire and cable are not given to the model. (4) There is room for supplementary development.

At present, there are still some differences between China's standards and IEC international standards. Because some standards, IEC is promulgated after China's standards, according to the principle of equivalent adoption of international standards, this difference will be eliminated in the future.

3 Models and instructions for use 3.1 About flame retardant (ZURAN)

According to IEC 332, flame retardant has single and bundled points. More than a decade ago, China's wire and cable were mainly halogen-containing products such as polyvinyl chloride and chloroprene rubber. Passing a single vertical burning test was a basic requirement in the product standard, so it was not necessary to give a single flame-retardant model. The bundled C class is regarded as the basic requirement of the flame-retardant wire and cable, and the B class and the A class are the flame retardant requirements that the user must specify. Therefore, the use of the flame-retardant (ZURAN) first letter ZR as a model is also prevalent.

The situation is different now. Polyolefins such as polyethylene, polypropylene, ethylene propylene, natural monobutylene, etc. are flammable materials. When their flame-retardant products can pass a single vertical combustion test, they should be given a model to match the original flammability characteristics. the difference. This model uses Z. Due to the flame-retardant A, flame-retardant B, flame-retardant C, and flame-retardant D, the bundled combustion is distinguished by ZA, ZB, ZC, and ZD models. Among them, flame retardant D is a new proposal of IEC and is applicable to wire and cable with an outer diameter of 12mm and below. The total volume of non-metal materials used in the sample is only 1/3 of that of Class C, ie 0.5 L/m. The requirement for a fire time of 20 minutes and a scorch height of less than 2.5 m is the same as for Category C. Because this proposal has yet to be voted on.

In addition, IEC 332-3 has a provision that, when performing Class A tests, if the samples are arranged at intervals (where there is a core conductor larger than 35 mm2), they can be arranged behind the standard ladder, and they can be arranged behind and used AF/R. Indicated. Or use a wide ladder (0.8m wide) in front of the ladder (indicated by AF) and use a double torch for the fire. However, if a large size cable is placed in front of a standard ladder, a single torch is used for the fire and is still denoted as AF. In order to simplify the model, for this type of situation are recorded as ZA.

3.2 About fire resistance (NAIHUO)

According to the Chinese standard GB 12666.6-90, fire-resistance is divided into Class A and Class B. The fire temperature for Class A is 950°C to 1000°C, and the fire temperature for Class B is 750°C to 800°C. Previously, NH models were used to represent fire-resistant wire and cable, which was equivalent to Class B in our country's standard according to IEC 331-1970. Because some users require Class A fire-resisting wire and cable, the model is expanded to NA and NB to show the difference. However, in the latest IEC newly published standard IEC60331-1999, the temperature for the supply of fire is still 750C ~ 800 °C, and the proposal to increase the test temperature is still under consideration. Therefore, if the adoption of a new national standard is equivalent, there is no Class A B class distinction for fire resistance rating. At that time, the model of fire-resisting wire and cable can be simplified as a team. If the IEC will classify the test temperature in the future, our model will have room for development.

It is worth noting that the United Kingdom has the most tricks for fire-resistant cables and there are many models. Taking into account the impact of the United Kingdom on IEC, IEC is considering increasing the test temperature, water spray and mechanical impact. Therefore, additional impact (CHONGJI) with model C, additional water spray (PENSHUI) with model S for future use .

Note: Fire resistance, water spray fire resistance, and impact fire tests are performed separately. For example, the cable type with the impact resistance of 950°C for 3h and 750°C is CY; the cable type for the 3h fire resistance at 650°C, 20min fire resistance at 950°C, water spray at 650°C and 650°C impact is ASWX, and so on. Its highest level model is CwZ.

3.3 About DILU, WULU Low Smoke (DIYAN), Low Capacity (DIDU)

About DILU, it is represented by D. The HCI content was determined by the method of IEC 60754-1:1994 (GB/T 17650.1-1998). There are no indicators in the standard and HCI ≤ 100 mg/g is recommended.

With regard to WULU (low-corrosion), ie, low corrosion, denoted by W: with IEC 60754-2:1991 (1997 revision), the national standard equivalently adopted in China is determined by GB/T17650.2-1998 method, and the target is PH≥4.3. r (conductivity) ≤ 10ps/mm. Many foreign countries or companies have set halogen-free standards as HCI ≤ 5mg/g, and people in China have also followed suit. This is inappropriate. Because IEC 60754-1 has explicitly stated that this method cannot be used to determine a material with an HCI content of less than 5 mg/g, "halogen free" cannot be determined. Secondly, when the HCI content is >2 mg/g, the pH of the aqueous solution is less than 4.3, which is inconsistent with the requirements of IEC 60754-2. In addition, some people think that the IEC fixed index PH ≥ 4.3, and the German index is PH ≥ 3.5, so the IEC requirements higher than Germany. This is only a superficial phenomenon. In fact, the effect of both is exactly the same. I have the opportunity to introduce another article.

Regarding low smoke (DIYAN), it is also represented by D. Although it repeats with the low-halogen D, it has already been adopted and it is not misunderstood when the model is assembled. Low smoke international standards require a light transmission rate of ≥ 60%. It must be pointed out that our country's PVC-based low-halogen low-smoke material made of the wire and cable, its low smoke can not meet the above requirements, should not use low smoke models. Unless otherwise stated in the product standard, such as the indicator of reducing light transmittance, and indicating that the indicator is lower than the requirements of international standards or national standards, so as not to mislead the user.

Regarding low toxicity (DIDU), it cannot be represented by D, but U. The relevant standard IEC is still under consideration. The most commonly used is the British Navy's engineering standard NES713, which is expressed in terms of the toxicity index (TI). For example, the insulating material has a toxicity index of less than 3 and the jacket has a toxicity index of less than 5. Some domestic manufacturers claim that they can provide halogen-free, low-smoke and non-toxic cables. The non-toxic substances mentioned here are not appropriate and should be low-toxic. Because halogen-free and low-smoke materials burn toxic CO when they are burned, if the material contains P, N, and S, more toxic gases are generated.

3.4 Combination of Models When a certain ~ wire and cable has a variety of combustion characteristics, according to international practice, a certain model and appellation in the following order (no items should be omitted);

No (low) halogen-low smoke-low toxicity-flame-retardant-fireproof

(1) Flame-retardant (A) PVC insulated PVC sheathed power cable, type: ZA-VV

(2) Low halogen flame retardant (B) PVC insulated PVC sheathed power cable, model: DZB-VV

(3) Low-halogen low-smoke flame-retardant (C) PVC insulated PVC sheathed power cable, model: DDZC-VV

(4) Halogen-free and low-smoke flame-retardant (A type) cross-linked polyethylene insulated steel tape pinned polyolefin sheathed power cable, model number: WDZA-YJY23 (polyolefin jacket with outer sheath 3)

(5) Halogen-free low-smoke flame-retardant (B-type) XLPE insulated polyolefin sheathed power cable, model: WDZB-YJY (for polyolefin models with Y do not use X, E, O or P, according to GB/T13849 -1993)

(6) Halogen-free low-smoke fire-retardant (A type) XLPE insulated polyolefin sheathed power cable, model: WDNA-YJY

(7) Fire-retardant (B) PVC insulated PVC sheathed power cable, model: NB-VV

3.5 Must pay attention to the problem The method of determining the corresponding model and appellation according to the burning characteristics of the wire and cable is proposed above. Here are some of the current problems and how to deal with them as follows: (1) Do not give flame-retardant hats To make the wire and cable meet the flame-retardant requirements, there are various methods.

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