EW September 2016

Technical article

September 2016

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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.

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.

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

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

4.2.2.1 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

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

Test

Specified value

Acceptance criteria

(1,550nm)

Attenuation of cable

IEC 60793-1-40

1,310nm

1,550nm

≤0.4dB/km

≤0.3dB/km

Tensile

IES 60794-1-2-E1

1,350N for 1 min

∆

≤0.1dB/km,

fibre strain≤0.6%,

No damage to

cable outer sheath

Crush according to

IEC 60794-1-2 E3

500N/10cm for 1 min

∆

≤0.1dB/km,

No damage to

cable outer sheath

Water penetration

IEC 60794-1-22 F5

3m sample, 1m depth of

water for 24h

No penetration

Temperature cycling

IEC 60794-1-22 F1

-20˚C/+60˚C,

two cycles

∆

≤0.1dB

Vertical flame propagation

for single sample

IEC 60332-1-2

600mm sub-unit sample,

60s flame application

The distance between

the lower edge of the top

support and the onset of

charring is greater than

50mm

Fibre strain: 0.235%

▲

Table 1

Overview of requirements of the flat cable

▲

Figure 1

Tensile performance for the cable

▲

Figure 2

The anchor clamp used to fix cable