Cable FAQs

FAQs

In order to serve our customers better we have listed some of the most frequently asked questions with regards to product details, construction standards and technical terminologies. If your questions are not listed below feel free to email us with your query.

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1.What is LSF?

LSF is abbreviation used for Low Smoke and Fumes compound. It is used in special application where the cable is required to emit low smoke and no halogen acid gases in the event of a fire. With low smoke emission the exit signs are clearly visible to people for escape. As this material does'nt contain halogens it does not give off acidic gases when burning. The same compound is also known with following abbreviations,

LSZH – Low Smoke Zero Halogen

LSOH - Low Smoke Zero Halogen

2. Why does Zero Halogen Material have a test limit of 0.5% Halogen content?

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

3.What is the operating temperature of PVC insulated building wire & XL-LSF insulated building wire?

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.

4. What is G/Y in core identification?

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.

5. What is the new/old core colour scheme for core identification of cable?

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.

No. of cores Old core colours New core colours
2 Red, Black Brown, Blue
3 Red, Yellow, Blue Brown, Black, Grey
4 Red, Yellow, Blue, Black Brown, Black, Grey, Blue

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.

6.What does U0/U (Um) mean in voltage designation of a cable?

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)

7.What is the difference between 6/10 kV & 6.35/11 kV voltage grade?

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.

8.What are the application areas of Mica Glass Taped - Fire Resistant (FR) cables?

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 eg. fire detection, fire alarm etc
  • Power supply to equipment used in fire fighting eg. sprinkler pumps, smoke extractors
  • Services where circuit integrity is very important under fire conditions eg. special equipments in hospital
9.What is the minimum installation bending radius of cable?

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.

10.Why is it that some times the drums supplied have a smaller bending radius than recommended for installation?

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

11.What does Type Test mean?

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.

12.What is the range of approval for Type Test?

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.

13.What are different types of outer sheath & their applications?

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

Material Key properties Recommended for
PE High mechanical strength Direct burial, duct installation
PVC Flexibility & flame retardance General purpose
LSF Zero halogen , low smoke Mass transit system, high rise building, public areas & confined locations.
14.Why Ducab does not make LSF cable with Graphite coating?

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.

15.Why does Ducab not recommend PVC cables 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.

16.Why does Ducab recommend semicon bedding tape below copper wire screen?

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.

17.What are the guaranteed properties of RP-PVC?

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.
18.Why UV radiation resistant insulation is expected to have better life?

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.

19.Why are the dimensions of Ducab’s MV cable less than those of Ducab’s competitors?

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.

20.What are C-W-Z tests? Why it is so significant for FR cables?

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.

21.What are the differences between RP-PVC & LSF? Why does Ducab sometimes recommend RP-PVC in place of LSF ?

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.

22.Is there any special installation condition for LSF cables?

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

23.Power cables are robust and black PVC sheath are UVR protected then why does Ducab recommend cable installation under a shade?

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.

24.What is the design service life of MV power cable?

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.

25.What information does Ducab need to quote a cable, which meets customer’s requirement?

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.

26.What is Partial Discharge (PD) testing?

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.

27.Does Ducab do any installation or pre-commissioning / High Pot test on MV/LV cables?

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

28.Can we carry out a sheath electrical test on all the cables manufactured by Ducab?

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

29.What is VLF test and is it better than a DC test?

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.

30.Are on-site VLF tests or on-site PD tests and Diagnosis tests carried out by Ducab?

No. Ducab does not carryout any test at site.

31. Does Ducab manufacture any cables for installation in water?

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