EuroWire September 2016

Technical article

3.2 Different combinations of materials of the flat cable The flat cable was a tight-structure cable, but after stripping 20-30cm of the outer sheath, the sub-unit cable could not adhere to the outer sheath. Moreover, the flat cable must meet the requirements of flame retardancy. Therefore, the outer sheath and sub-unit materials both have the flame retardant property and high temperature resistance property. Taking the users’ actual needs and the application environment of the cable into consideration, three different com- binations of materials of the flat cable were designed to verify the processing performance and the overall performance of the cable. That is, three different combinations of sub-unit material and outer sheath material. The first combination was HDPE (high-density polyethylene) outer sheath material and PVC (polyvinyl chloride) sub-unit material. The second combination was LSZH (low smoke zero halogen) outer sheath material and PVC sub-unit material. And the last combination was LSZH outer sheath material and LSZH sub-unit material. After the cable structure was set, the mould was designed according to the materials’ behaviour and the processing parameters adjusted continually to settle various problems that appeared during the cable processing. This then underwent repeated processing verification, and it was found that the first and the second designs of the cable could satisfy the stripping requirements. That is to say, the flat cable with HDPE outer sheath and PVC sub-unit, or with LSZH outer sheath and PVC sub-unit could both assure that the sub-unit cable did not adhere to the outer sheath after 20-30cm of the outer sheath was stripped. For the last design, the LSZH outer sheath materials and the LSZH sub-unit materials easily adhered to each other. Although this could produce a small amount of sample to meet the stripping requirements, the continuity and consistency of processing for the cable could not be guaranteed, so it was not recommended to adopt this structure.

Acceptance criteria (1,550nm)

Test

Specified value

α ≤0.4dB/km α ≤0.3dB/km

Attenuation of cable IEC 60793-1-40

1,310nm 1,550nm

∆ α ≤0.1dB/km, fibre strain≤0.6%, No damage to cable outer sheath ∆ α ≤0.1dB/km, No damage to cable outer sheath

Tensile IES 60794-1-2-E1

1,350N for 1 min

Crush according to IEC 60794-1-2 E3 Water penetration IEC 60794-1-22 F5 Temperature cycling IEC 60794-1-22 F1

500N/10cm for 1 min

3m sample, 1m depth of water for 24h

No penetration

-20˚C/+60˚C, two cycles

∆ α ≤0.1dB

The distance between the lower edge of the top support and the onset of charring is greater than 50mm

Vertical flame propagation for single sample IEC 60332-1-2

600mm sub-unit sample, 60s flame application

▲ ▲ Table 1 : Overview of requirements of the flat cable

Fibre strain: 0.235%

▲ ▲ Figure 1 : Tensile performance for the cable

▲ ▲ Figure 2 : The anchor clamp used to fix cable

according to the specification and fully met the client’s requirements and needs. A main series of tensile and crush tests had been performed and the relevant results are listed in Figures 1 and 4 . 4.2.2.1 Tensile test The client’s requirements for tensile performance were a maximum fibre strain of 0.6 per cent and a maximum attenuation increase of 0.1dB for a requested 1,350N load dwell for 1 min. Furthermore, there should be no damage to the cable’s outer sheath. The test result showed that the maximum fibre strain was 0.235 per cent, as shown in Figure 1 . In addition, it was also found that the maximum short term additional attenuation was only 0.005dB and the maximum residual additional attenuation was just 0.003dB. In carrying out the tensile limit test of the cable, a special anchor clamp to fix the cable, as shown in Figure 2 , was used. The cable was loaded on the tensile testing machine and force applied until breakage took place, as shown in Figure 3 .

Table 1 shows an overview of the requirements of the cable. After the continuity and consistency of processing for the flat cable, severe measurement to the properties of the two qualified cables according to Table 1 were conducted. In the following sections, all the tests and results are described. 4.2 Test results 4.2.1 Transmission property The transmission property of the cable was measured by an OTDR (optical time domain reflectometer) according to IEC 60793-1-40. After testing, all the attenuation values of the flat cable with two different structures were below the limits, that is, the attenuation of the flat cable was no more than 0.4dB/km at 1,310nm, and no more than 0.3dB/km at 1,550nm. 4.2.2 Mechanical property The following mechanical tests were carried out according the IEC 60794-1-2 and IEC 60794-1-22 standards in order to make sure that all the parameters were

4 Main properties of flat cable 4.1 Performance requirements

All specifications of the flat cable are determined by the installation and the usage of the cable.

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September 2016