Essential knowledge for wire and cable inspection - Vertical burning test of single wire and cable

I. Inspection Purpose

When wire and cable products experience short circuits or come into contact with fire sources, the insulation or sheath may catch fire. In many places where strict fire prevention is required (such as coal mines, ships, underground railways, etc.), it is required that in the event of a fire, the flame should not spread but extinguish itself within a certain period of time and length. This is called non-flame-retardant property. In some cases, if a product does not possess this performance, it will lead to very serious consequences.

Products that require non-flame-retardant performance generally use polyvinyl chloride, chloroprene rubber, nitrile polyvinyl chloride compound, and chlorinated polyethylene as insulating and sheathing materials. When these materials are burned, they release chlorine gas, which plays a flame-retardant role. Sometimes, in order to enhance the flame-retardant effect, certain flame retardants are also added. Other materials such as polyolefin can also meet the performance requirements of flame retardancy (and its low smoke zero halogen) by adding flame retardants, etc.

Ii. Scope of Application

The DZ-1 method is applicable to all kinds of wires and cables.

2. The DZ-2 method is applicable to insulated wires with solid copper conductors of 0.4 to 0.8mm in diameter and stranded conductors of 0.1 to 0.5mm² in cross-section.

Iii. Inspection Basis

GB/T 18380.11-2008/IEC 60332-1-1:2004

GB/T 18380.21-2008/IEC 60332-2-1:2004

Iv. Test Equipment and Apparatus

1. Combustion test instrument

2. Fire source: Gas blowtorch in compliance with IEC 60695-2-4/1.

V. Sampling and Testing Equipment

1.DZ-1 method

A sample of 600±25mm in length is cut from the finished wire or cable. Before the test, all samples should be treated at (23 ±5) ℃ and a relative humidity of (50±20) % for at least 16 hours. If there is a coating of paint or varnish on the surface of the wire or cable, the sample should be kept at 60±2℃ for 4 hours before the test, and then the above treatment should be carried out.

2.DZ-2 method

Two samples with a length of 600±25mm were cut from the finished wires and cables and numbered as 1 and 2 respectively. If the surface of the sample is coated with paint or varnish, it should be kept at 60±2℃ for 4 hours before the test and then cooled to room temperature.

Vi. Test Procedures

The first method (DZ-1 method

1. Sample outer diameter and fire supply time:

2. The sample should be bound to two horizontal supports with 1mm² copper wire. The distance between the bottom end of the upper support and the top end of the lower support should be 550±5mm, and the lower end of the sample should be approximately 50mm from the base plate.

3. Light the blowtorch and adjust the gas and air flow rates. The position of the blowtorch should be such that the tip of the blue inner cone touches the surface of the sample. The contact point should be 475±5mm away from the lower edge of the upper support, and the axis should be at a 45° Angle to the axis of the sample.

4. During the test, the flame of the blowtorch should continuously burn the sample until the residual flame on the sample goes out by itself at the end of the specified fire supply time.

5. At the end of the test, remove the blowtorch and extinguish the flame.

6. Wipe the sample clean. Measure the distance between the charred part and the lower edge of the upper fixture.

The differences between the second method (DZ-2 method) and the DZ-1 method are as follows:

1. Flame intensity

Make the longitudinal axis of the nozzle perpendicular to the horizontal plane, close the air inlet, and adjust the propane flow rate to make the total length of the luminous flame 125±25mm.

2. Installation of the sample

Hold Sample No. 1 vertically and clamp it so that it is in a vertical position at the center of the metal cover. The specimen should be subjected to a tension of 5N/mm ² based on the cross-sectional area of the conductor.

2) The intersection Angle between the centerline of the blowtorch and the centerline of the sample is 45°. The distance from the nozzle to the surface of the sample measured along the centerline of the blowtorch should be 10±1mm. The distance from the intersection point of the centerline of the blowtorch and the centerline of the sample to the fixed point for applying a 5N/mm² load or the upper edge of the lower fixture should be 100±10mm. The distance to the lower edge of the upper fixture should not exceed 465mm.

3. Fire supply time

The sample was burned with a blowtorch flame, and the maximum supply time was 20±1 second. If the conductor in the test does not melt, the test is over. If the conductor of the sample melts prematurely, the time t (s) when it melts should be recorded, and the test should be reconducted with sample No. 2, with the fire supply time changed to (t-2) s.

4. Burning

During the test, the flame of the blowtorch should continuously burn the sample until the residual flame on the sample goes out by itself at the end of the specified fire supply time.

2) Take out the sample, wipe it clean, and measure the distance from the charred part to the lower edge of the upper fixture.

Vii. Evaluation of Test Results

DZ-1 method: If the charred part is less than 50mm from the lower edge of the upper fixture, the test result is judged as qualified. In addition, if the burning extends downward to a distance greater than 540mm from the lower edge of the upper support, it will be judged as unqualified.

DZ-2 method: If the test results meet the following requirements, the test results are determined to be qualified.

The carbonized part should not reach within 50mm from the lower edge of the upper fixture.

2. If the conductor of the sample melts prematurely and sample No. 2 is used for re-testing, the carbonized part should not reach within 50mm from the lower edge of the upper fixture. Only Test 2 is used as the basis for evaluation.