Tests on Electric Cables under Fire Conditions — Part 3: Tests on Bunched Wires or Cables
1 General
1.1 Scope
This standard describes a method of type approval testing to define the ability of bunched cables to restrain flame propagation in defined conditions regardless of their application, i.e. power, telecommunications (including data transmission and optical fibre cables), etc.
Three categories are defined and distinguished by test duration, and the volume of non-metallic material of the sample under test (see Table 1); they are not necessarily related to different safety levels in actual cable installations. Category A has two designations for the method of mounting.
1.2 Normative References
The following normative document contains provisions which, through reference in this text, constitute provisions of this standard. At the time of publication, the edition indicated was valid. All normative documents are subject to revision, and parties to agreements based on this standard are encouraged to investigate the possibility of applying the most recent edition of the normative document indicated below.
GB/T 18380.1-2001 Tests on Electric Cables under Fire Conditions — Part 1:Test on a Single Vertical Insulated Wire or Cable (idt IEC 60332-1:1993)
GB/T 18380.2-2001 Tests on Electric Cables under Fire Conditions — Part 2: Test on a Single Small Vertical Insulated Copper Wire or Cable (idt IEC 60332-2:1989)
GB/T 2951.3-1997 Common Test Methods for Insulating and Sheathing Materials of Electric Cable — Part 1: Methods for General Application — Section Three: Methods for Determining the Density — Water Absorption Tests — Shrinkage Test (idt IEC 60811-1- 3:1993)
2 General Detail of Test Procedures
2.1 Test sample and categories
The test sample should comprise a number of test pieces of cable from the same length, each having a minimum length of 3.5 m.
The total number of 3.5m test pieces in the test sample should be in accordance with one of the three categories as follow:
Category A: The number of test pieces required to provide a nominal total volume of non-metallic material of 7 L per metre.
Category B: The number of test pieces required to provide a nominal total volume of non-metallic material of 3.5 L per metre.
Category C: The number of test pieces required to provide a nominal total volume of non-metallic material of 1.3 L per metre.
2.2 Details of the test rig
2.2.1 Enclosure and air supply
The test rig (Figure 1) should comprise a vertical test chamber having a width of 1 000 mm ± 100 mm, a depth of 2 000 mm ± 100 mm and a height of 4 000 mm ± 100 mm; the floor of the chamber should be raised above ground level. The test chamber should be nominally airtight along its sides, air being admitted at the base of the test chamber through an aperture of 800 mm ± 20 mm x 400 mm ± 10 mm situated 150 mm ± 10 mm
from the front wall of the test chamber.
The air flow should be adjusted to a rate of 5 000 L/min ± 500 L/min at a constant controlled temperature of (20 ± 10)°C and measured at the outlet or inlet side before the test commences. These parameters should be preferably regulated during the test.
An outlet (300 mm ± 30 mm) x (1 000 mm ± 100 mm) should be made at the rear edge of the top of the test chamber. The back and sides of the test chamber should be thermally insulated to give a coefficient of heat transfer of approximately 0.7W/(m2·K). For example, a steel plate 1.5 mm to 2.0 mm thick covered with 65 mm of mineral wool with a suitable external cladding is satisfactory (see Figure 1a). The distance between the ladder and the rear wall of the chamber is 150 mm ± 10 mm, and between the bottom rung of the ladder and the ground 400 mm ± 5 mm. The clearance between the lowest point of the test piece and the ground is approximately 100 mm (see Figure 3).
2.2.2 Ladder types
There are two types of ladder: a standard ladder of 500 mm width and a wide ladder of 800 mm width. Details of the types of ladder and the methods of mounting to be used are provided in Clauses 3 to 5 of this report (see Figures 2,2a, 3, 3a, 3b, 3c and 3d).
2.2.3 Smoke cleaning attachment
Legal requirements may make it necessary for equipment for collecting and washing the smoke to be fitted to the test chamber. This equipment should be such as to collect the smoke leaving the chamber without causing a change in the air flow rate through the test chamber.
2.3 Determination of number of test pieces
In order to calculate the appropriate number of test pieces, it is necessary to determine the volume per metre of non-metallic material of one test piece.
A section of cable which should not be less than 0.3 m is carefully cut to ensure that the surfaces are at right angles to the cable axis, thus enabling precise measurements of its length.
Each non-metallic material Ci should be extracted from the test piece and weighed. Any less than 5% of the total non-metallic weight should be discarded.
Where semi-conducting screens cannot be removed from the insulating material, the components may be considered as one for the purpose of measuring their weight and specific gravity.
The specific gravity of each non-metallic component (including cellular material) should be measured in an appropriate way, e.g. Clause 8 of GB/T 2951.3-1997, in order to obtain values expressed to the second decimal place. Tapes and fibrous components should be assumed to have an effective specific gravity of 1.
The volume Vi (L/m of cable) of each non-metallic material Ci is calculated as follows:
Where,
Mi—the mass of the component Ci (kg);
—the specific gravity of the component Ci, kg/dm3;
l—the length of the section of cable (m)
The total volume, V, of the non-metallic materials contained in one metre of cable is equal to the sum of the individual volumes V1, V2, etc.
The closest integer (0.5 and above corresponding to 1) of the number of test pieces to be mounted is obtained by dividing the volume per metre of the test category specified in clause 2.1 of this section by the total volume, V, of non-metallic material per metre of cable.
2.4 Mounting of the test sample
The methods of mounting the pre-determined number of test pieces to form the test sample are fully described in Clauses 3, 4 and 5.
Two methods of mounting (designations F/R and F) are applicable to category A. Only designation F applies to categories B and C.
For identification purposes the following abbreviated notations may be used:
Category A, designation F/R ××××.3A F/R
Category A, designation F ××××.3AF
Category B, designation F ××××.3B F
Category C, designation F ××××.3CF
2.5 Ignition source
The ignition source should be one or two ribbon-type propane gas burners and their own set of flow meters, complete with venturi mixer, and whose flame-producing surface consists of a flat metal plate 341 mm long and 30 mm wide through which 242 holes of1.32 mm in diameter are drilled on 3.2 mm centres in three staggered rows of 81, 80 and81 holes each to form an array having the nominal dimensions 257 mm x 4.5 mm as shown in Figure 4. As the burner plate may be drilled without the use of a drilling jig, the spacing of the holes may vary slightly. Additionally, a row of small holes may be milled on each side of the burner plate to serve as pilot holes with the function of keeping the flame burning.
Each burner should be fitted with an accurate means of controlling the fuel and air input flow rates. Figure 5 shows an example of a control system. The calibration of the propane rotameter should be checked after installation with a flow meter to ensure that the pipework and the venturi have not affected the calibration.
Corrections for the variations in temperature and pressure from that specified on the propane rotameter should be applied when necessary.
For the purpose of this test, the air should have a dew-point not higher than 0°C and the- input should be 76.7 L/min ± 4.7 L/min; the propane flow rate should be 13.3 L/min ± 0.5 L/min at one atmosphere and 20°C to provide a nominal (73.7 ± 1.68) MJ/h (70 000 ± 1 600 Btu/h) to each burner.
Note: The net heat of combustion is used to calculate the propane flow rate.
2.6 Positioning of ignition source
For the test the burner should be arranged horizontally at a distance of 75 mm ± 5 mm from the front surface of the cable sample and 600 mm ± 5 mm above the floor of the test chamber. The point of application of the burner flame should lie in the centre between two cross-bars on the ladder and at least 500 mm ± 5 mm above the lower end of the sample (see Figure 3).
Adjustment of air and gas flows prior to the test may be carried out away from the test position.
Where two burners are used in tandem for the test category A designation F in combination with the wide ladder - see Clause 3 - they should be positioned as shown in Figure 4a.
2.7 Test procedure
2.7.1 Test conditions
The test should not be carried out if the external wind speed measured by an anemometer fitted on the top of the test rig is greater than 8 m/s and should not be carried out if the temperature of the inside walls is below 5°C or above 40°C measured at a point approximately 1.5 m above floor level, 50 mm from a side wall, and 1.0 m from the door. The enclosure door shall be closed throughout the test.
The cables or test pieces forming the test sample should be conditioned at a temperature of (23 ±5)°C for at least 16 h before commencing the test. The test chamber should be dry.
2.7.2 Flame application times
See Clauses 3,4 and 5.
2.8 Performance requirements and retest procedure
2.8.1 Performance requirement
After burning has ceased, the test sample should be wiped clean. If burning has not ceased after a maximum time of 1 h from the completion of the test flame period, the flame should be extinguished.
1 General
2 General Detail of Test Procedures
3 Method of Mounting Test Samples and Flame Application Times for Category A, Designation F/R or F
4 Method of Mounting Test Samples and Flame Application Times for Category B, Designation F
5 Method of Mounting Test Samples and Flame Application Times for Category C, Designation F
