FAQs

LSF material does not contain halogen but the test method has an accuracy of +/- 0.5% therefore the specification has this value.

Building wires are manufactured to BS 6004. For general purpose, they are insulated with TI1 PVC insulation, which has operating temperature of 70°C.

In case higher operating temperature and higher current carrying capacity is required then type TI3 PVC insulation can be offered which has operating temperature of 90°C. In the case of XL-LSF insulated building wire, the operating temperature is 90°C.

It is the colour identification offered by means of bi-colour combination Green/Yellow colours. This colour combination is used for earthing. The distribution of colours is such that one of the colour covers at least 30% of the surface of the core while the other colour covers the remainder of the core surface.

The old and new colour scheme is as per the following table, the new colour scheme has been adopted in British Standards to have a more standard colour code across Europe. It is not compulsory to change colours in the UAE.

Please note that the neutral core colour in the old colour scheme is Black, which is changed to Blue. The three phase colours are changed from Red, Yellow, Blue to Brown, Black, Grey in the new colour scheme.

In the voltage designation of cables U0/U (Um):

U0 is the rated power frequency voltage between conductor and earth or metallic screen for which the cable is designed

U is the rated power frequency voltage between conductors for which the cable is designed

Um is the maximum value of the “highest system voltage” for which the equipment may be used (see IEC 60038)

There is no difference, both these voltage grades are same with highest system voltage Um = 12 kV.

The XLPE insulation nominal thickness for cables with this voltage grade is 3.4 mm as per IEC 60502-2 (2005) as well as BS 6622 (2007) specifications. Hence the same cable may be termed as 6/10 kV voltage grade as per IEC 60502-2 OR 6.35/11 kV voltage grade as per BS 6622.

Fire resistant cables manufactured by Ducab as per BS 7846 have special grade mica tape wrapping over the conductor. Mica as a mineral retains its insulation property even in case of extreme fire temperatures of up to 950°C. Mica tape over the conductor forms a tube when subjected to fire & provides a barrier to insulate the conductor and prevent short circuit. The areas of application for these cables include,

• Essential safety circuits e.g. fire detection, fire alarm etc
• Power supply to equipment used in firefighting e.g. sprinkler pumps, smoke extractors
• Services where circuit integrity is very important under fire conditions e.g. special equipments in hospital

The minimum bending radius of cable is that radius below which the cables should never be bent. The minimum bending radius depends upon the type, voltage grade and construction of the cable. This value is provided wherever required by the customer. In practice wherever possible a generous bending radius should be used.

Cables are supplied on the drums and are used only for transporting the cable from one place to other. Bending on the drum is carried out under controlled conditions in the manufacturing plant.

Type tests are the tests made before supplying, on a general commercial basis, a type of cable in order to demonstrate satisfactory performance characteristics to meet the intended application. These tests are of such nature that after they have been made, they need not be repeated, unless changes are made in cable materials or design or manufacturing process which might change the performance characteristics.

When type tests have been successfully performed on a type of cable with a specific conductor cross sectional area and rated voltage, the type approval is accepted as valid for cables of the same type with other conductor cross sectional areas and/or rated voltages subject to satisfaction of conditions set out in the IEC specification.

Different types of outer sheath and their applications are as below.

LSF is for applications requiring Low Smoke and Fumes whereas Graphite, being carbon, burns easily and generates smoke, which is contradictory to LSF. Hence LSF cables are not offered with graphite coating.

Graphite coating is applied to cables to enable electrical testing of the outer sheath. If it is important for the outer sheath to pass such a test Ducab will always recommend PE as the sheath material. PE has a higher electrical strength than PVC and is much more resistant to moisture. Moisture will readily penetrate PVC and degrade the electrical strength.

For all cables while in service during load cycles there is expansion and contraction of the cores. The copper wires cannot expand to the extent of XLPE insulation. Hence there is a chance of the copper wires being pushed into the insulation. The semi-conductive bedding tape provides a cushion and protects the core surface from the damage.

There are 3 main properties:

• Oxygen Index more than 30.
• Halogen (Acid gas) content less than 20%
• Mechanical & Electrical properties to meet requirements of Type – 9 of BS: 7655.

Polymers (specially Polyethylene) are known to be susceptible to UV radiation. Exposure to UV radiation for prolonged duration may result in developing surface-cracks. Hence Ducab add a special Ultra Violet Radiation resistant stabilizer package in the insulation materials. This protects the insulation from deterioration.

Maintaining minimum dimensions of any specification and manufacturing cables depend on two factors:

• Quality of material (Excellent insulating grades have very high di-electric strength and electrical break-down stress or conductivity of electrolytic grade copper is much higher than commercial grade copper)
• Manufacturing technique & process capability (eg. High process capability indicates stricter control on tolerance, e.g. eccentricity of insulation allowed less than 10%)

Ducab cables excel on both the counts, hence cables are manufactured keeping in view the optimum dimensions, which makes the cable slimmer, uses less material and at the same time makes them more efficient.

C-W-Z tests are referenced in BS: 6387, which is called for by cable standards such as BS: 7846. These letters refer to standards of fire resistance

• C – Test with fire only.
• W – Test with fire and water spray.
• Z - Test with fire and mechanical shock applied simultaneously during burning.

To meet the "C" category the cable has to maintain circuit integrity while subjected to fire at 950°C for three hours. To check “W” category, the cable is sprayed with water while also subject to fire to simulate the effect of an activated sprinkler system. In the “Z” category, the cable is subjected to mechanical shocks during the fire test to simulate falling debris. During all of these tests the cable carries electricity at rated voltage.

These tests are highly significant as they actually simulate the fire conditions under which the FR Cables are expected to perform.

C-W-Z tests are referenced in BS: 6387, which is called for by cable standards such as BS: 7846. These letters refer to standards of fire resistance

• C – Test with fire only.
• W – Test with fire and water spray.
• Z - Test with fire and mechanical shock applied simultaneously during burning.

RP-PVC contains halogen whereas LSF does not contain Halogen.

Ducab recommend RP-PVC for jacketing of cables, which are not used in areas of high population density but have a critical requirement for reduced fire propagation.

Yes, Ducab issue a special instruction detailing the conditions to be observed during storing and installation of LSF cables.

Cable installation under shade is essential to prevent heating by direct sunlight. Heating from the ambient conditions will reduce the current rating adversely as the cable will reach its maximum temperature when carrying reduced load.

If the cable is installed following the best practices, not overloaded then the expected service life of a MV cable is more than 25 years.

Clear statement about required load, system voltage, route length, installation conditions, environment e.g. thermal resistivity of soil or air temperature etc, number of circuits, distance between two circuits, earth fault current and 3 phase short circuit current.

Discharges in a cable are caused by the breakdown of the gas contained within voids in the insulation. These tiny electrical discharges release electrical charge, which can be detected using highly sensitive equipment. The voltage at which the breakdown first occurs is known as the discharge inception voltage and the charge is measured in picoCoulombs (pC). These discharges can lead to cable failure in service so it is vital to detect them during routine test of each cable length.

Specifications for MV polymeric cable all require measurement of partial discharge and define the maximum level of discharge acceptable at particular test voltages. However, any discharges detected within a cable should be identified and eliminated even if found to be below the specification limit.

Installation and commissioning tests for any cables are not done by Ducab. We recommend that contractors follow the IEC recommendations.

The sheath test can only be carried out on cables with a semi-conductive coating on the outer sheath.

Using AC test equipment for on-site testing of MV cables is not cost effective. The DC site test has been used for many years but some research suggests that it is not completely effective and in some cases may cause harm to polymeric cables.

VLF testing is an alternative method, which is based on AC testing, but it is carried out at a Very Low Frequency (VLF). By generating very low frequency (VLF) down to 0.1 Hz (instead of power frequency), it is possible to reduce the required power for charging the cable capacitance.

No. Ducab does not carryout any test at site.

Cables produced by Ducab are meant for distribution networks and industrial installations and are not designed for submarine applications.