Cable Gland Interview Questions & Answers

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Cable Gland Interview Questions & Answers

With the continuous growth in the electrical industry and automobile industry, the demand for cable glands has also increased multiple folds. And with the increase in production of cable glands, the need for Cable Gland machine operators has also moved up. Wisdomjobs gives you a wide range of options and multiple job opportunities where you can work as a cable gland operator. As a cable gland operator, you have to produce a wide range of components from different varieties of raw materials, while also adhering to the quality and procedures. A number of manufacturing businesses all around the world require specialized operators. The Cable Gland interview questions and answers prepared by us will help you easily grab one of these jobs.

Cable Gland Interview Questions

Cable Gland Interview Questions
    1. Question 1. What Are Different Elements Of A Cable? Basic About Cable Components & Constructional Details?

      Answer :

      Conductor:Conductor is a current carrying element made up of Aluminium or Copper with a specific cross section for the assigned rating, having resistance / km within certain specified limits.

      Electrical Insulation (dielectric): Insulation is provided over the conductors to electrically isolate them from one another. Various types of insulating materials used are : PVC, XLPE (Cross Linked Polyethylene), Rubber, etc.

      An insulated conductor is termed as Core. A cable may have one or more cores. In a multiple core cable , the cores are helically stranded together. In twin, three & multi-core cables, the cores are laid up together with a suitable lay; the outer most layer has right-hand lay and the successive layers are laid with opposite lay direction.

      Inner sheath (bedding): Cables with stranded cores are provided with Inner Sheath applied either by extrusion or by wrapping. It is ensured that the shape is as circular as possible. Inner Sheath is so applied that it fits closely on the laid up cores & it should be possible to remove it without damage to the insulation. Thickness of Inner Sheath is specified in relevant standard and is based on calculated diameter over laid-up cores.

      Armour: A wire, strip or a tape applied helically over the cable, to protect the cable from penetration by sharp objects, crushing forces, and damage from rodents or boring insects, is termed as Armour.

      Armour is applied over the insulation in case of single core cables & over inner sheath in case of twin, three & multi core cables.

      Outer Sheath: Outer sheath /Jacket is usually an extruded plastic cover over the laid-up or armoured core. PVC is a common sheathing material. Outer sheath provides mechanical, thermal, chemical and environmental protection. No electrical function is assigned to Outer sheath. The colour of outer sheath is normally black.

    2. Question 2. What Are Different Cable Types And Categories?

      Answer :

      Cables can be divided into large number of types based on a combination of classifications as follows:

      • Based on the voltage ratings as low voltage, high voltage, extra high voltage cables, etc.
      • Based on the conductor material, Copper conductor or Aluminium conductor.
      • Based on the insulating material as PVC insulated, Rubber insulated, XLPE insulated, etc.
      • Armoured or Unarmoured cables
      • Based on the sheathing material, as PVC Sheathed, Rubber Sheathed, Lead Sheathed, Aluminium Sheathed, etc.
      • Based on the number of cores as single core, two core, three core, three-and-a-half core, four core, multicore, etc.
      • Based on the cross-section of the conductor.
      • Based on the type of conductor, solid, stranded, sector shaped, etc.

      From above it is evident that the types of cables will differ widely depending upon various factors involved. To facilitate identification and description of the type of cable it is general practice to adopt some form of type designations. With these designations it becomes easier to convey in a few words the right type of cable.

    3. Question 3. Comparison Of Xlpe Cables With Pvc Cables?

      Answer :

      The important difference is the extra toughness of insulation and, in particular, the ability to withstand much high temperature without deformation due to mechanical pressure. The better physical properties of XLPE enable the insulation thickness to be reduced and hence overall size of the cable. The continuous temperature rating is increased from 70°C to 90°C and the temperature for short circuit ratings for the cable from 160°C to 250°C.

      In general, XLPE insulated cables are competitive alternative to PVC cables for industrial use and Paper insulated cables for public supply systems.

    4. Question 4. What Is Screening In Cable And Why It Is Required?

      Answer :

      Electrical Screening is necessary only for cables with phase voltage > 1 kv and fulfills the following functions.

      • Potential grading and limiting of electrical fields
      • Conduction of charge and discharge currents

      To satisfy these functions, the screening normally comprises a combination of conducting layers with metallic elements.

      The magnitude of electric stress and the degree of sensitivity of the insulation material against partial discharge govern the type of screening of the insulation with conducting layers.

      Above certain voltages, as a means of containing the electrical field within the insulation, semiconducting screens are applied over the conductor & insulation. Screens are provided to achieve symmetrical dielectric fields within the cable structure & carry current during short circuit. By this it is possible to eliminate any electrical discharges arising from air gaps adjacent to the insulation.

      The coefficient of expansion of polyethylene & EPR is approximately ten times greater than that of either Copper or Aluminium, and when the conductor is at its maximum operating temperature of 90°C a sufficiently large gap is formed between the insulation and the surface of the conductor to enable electrical discharge to occur. This discharge site & any others which are formed around a conductor when conductor is bent can be eliminated by applying a semiconducting layer over the conductor. Similarly, any discharges arising from air gaps between laid-up cores can be nullified by the use of a screen over the insulation.

      During the early 1960s semiconducting tapes were applied the conductor but these have since been superseded by an extruded layer. This has the advantage of providing both a smoother finish and, as it fills the interstices between the wires, a circular envelop around the conductor. By reducing the concentration of the flux lines around the individual wires, the electrical stress around conductor is reduced by between 10% to 15%. The semiconducting layer is compatible with, and bonds to, the insulation and a nominal thickness of 0.7 mm is typical.

    5. Question 5. What Is Frls H Cable?

      Answer :

      Flame Retardant Low Smoke and Low Halogen cables have improved flame resistant characteristics and emit lower smoke and toxic gases.

      Special features

      • Reduced flame propagation
      • Low smoke emission
      • Low acid gas generation

      Formulation for the FRLS compounds, which are mainly for the sheathing materials, require special ingredients. These cables may have insulation of PVC or XLPE, but sheath is PVC based, suitably compounded to meet FRLS H requirements.

    6. Question 6. What Are The General Packing Practices Followed?

      Answer :

      Cables are generally received on wooden/steel drum. There is an arrow painted on the flanges of the drum which indicate the direction in which the drum should be rolled. The cable will unwind and become loose if the drum is rolled in the opposite direction. All drums should be stored in such a manner as to leave sufficient space between them for air circulation. In no case should the drums be stored ‘ on the flat’ i.e. with flange horizontal.

    7. Question 7. What Are The Different Conductor Materials Used As Conductor?

      Answer :

      Conductor is a current carrying element made up of Aluminium or Copper with a specific cross section for the assigned rating, having resistance / km within certain specified limits.

    8. Question 8. What Is The Criterion For Selecting Particular Type Of Conductor?

      Answer :

      Conductor selection depends on various parameters like current carrying capacity , system voltage, voltage drop, flexibility, shape, and economics.

      The most commonly used metals are Copper and Aluminium.

      Resistance (R) of a conductor is inversely proportional to the area of cross section and is given by :

                             R= þ x l / A

      Where

      þ= Resistivity of the conductor material.

      l= Length of conductor.

      A = cross sectional area of conductor.

    9. Question 9. What Are The Parts Of Double Compression Gland?

      Answer :

      Parts of Double comp:

      • Gland body
      • Gland body Nut
      • Cone
      • Cone Ring
      • Neoprene Rubber seal
      • Rubber Washer
      • Check Nut

    10. Question 10. What Is Difference Between Single Compression And Double Compression?

      Answer :

      • Double compression glands provide extra support to the heavy armored cables entering or exiting the panel while single compression glands are used for light armored cables.
      • Normal Cable Gland is also called Single Compression Cable Gland. As the name suggests, while you tighten the gland, the grip or compression is effected only at one p [lace (i.e.) at the cable armour only. There is scope for moisture and corrosive vapour to enter the gland and thus into the cable.
      • Whereas in Double-Compression Gland, the compression happens both at the cable armour as well as at the inner sheath. This is sort of two sealing. Hence, chances of moisture or vapour entry are minimized. Hence these glands are also known as Weather-proof cable glands or Flame-proof cable glands.
      • The basic difference between single and double compression is in Single comp there no cone and cone ring.
      • The mechanical support for the cable is only Neoprene rubber seal, When you tighten the cable.
      • In double camp gland the mechanical support to the cable only cone and cone ring. When we are doing glanding the cable armor sits on the cone and cone ring act as a lock for armor.
      • Single compression and double compression glands are used on the basis of area classification. Those who are affiliated with oil and gas sector they will easily understand about area classification.
      • In zone 0 where the presence of hydrocarbon is obvious (IIC) double compression gland is used because the flame path in case of double compression gland is much more than in case of single compression gland.
      • The logic behind this is that if there is any explosion inside the terminal box of the motor no flame should be able to come out through the cable gland in order to prevent fire hazards but where there is no presence of hydrocarbons i.e. no danger of fire hazards (IIA/ IIB) single compression glands are used.
      • It has nothing to do with mechanical strength. Even in case of lighting fixtures used in IIC zone double compression glands are used.

    11. Question 11. What Are The Types Of Gland?

      Answer :

      • Brass Indoor Type Gland
      • Brass Outdoor Type Gland
      • Brass Straitening Unarmored Cable Gland
      • Brass Weather Proof Gland
      • PG Threaded Gland:
      • Industrial Type Gland

    12. Question 12. What Are The Type Of Cable And How The Gland To Be Used?

      Answer :

      Unarmored: Unarmored Cable will require outer seal within Gland to not only Provide ingress protection but also degree of retention.

      Armored: Gland that required clamping mechanism to terminate the armored both mechanically and electrically.

      The Gland will usually be required to provide ingress protection by sealing outer sheath and retention by clamping amour.

    13. Question 13. What Is Cable Gland?

      Answer :

      A device designed to permit the entry of cable in to electrical equipment which provides sealing, retention and ear thing, bonding, grounding, insulation, strain relief or combination of all these. Gland should maintain overall integrity of enclosure in to which it is to be fitted.

    14. Question 14. How To Select The Cable Gland?

      Answer :

      Gland should be selected on following Points:

      • Type of Cable
      • Gland Size
      • Entry Type/Thread Specification of application
      • Ingress Protection required.
      • Material

    15. Question 15. What Is The Function Of Conductor / Insulation Screen And Material Used?

      Answer :

      Function of Conductor / Insulation Screen:

      The conductor shield is a layer of semi-conducting material. Semi-conducting materials do not conduct electricity well enough to be a conductor but will not hold back voltage.

      It “smoothes” out the surface irregularities of the conductor. The conductor shield makes the voltage on the inside of the insulation the same. Industry specifications define the performance of conductor shield. Good insulation shields are extruded in tandem with the insulation.

      The insulation shield consists of two components. These components are the extruded (auxiliary) shield and the metallic (primary) shield.

      The extruded shield consist of a semi-conducting layer similar to the conductor shield. It makes the voltage on the outside of the insulation the same.

      The primary shield can consist of metal tape, drain wires or concentric neutral (CN) wires. Grounding the primary shield makes the voltage on the outside of the insulation ground. The Copper of the shield is usually bare, but may be coated with lead or tin. Some primary shields consists of drain wires and tape. Aluminium and lead can also be used as the shield.

      Concentric neutral wires serve a two-fold purpose. They function as the metallic component of the insulation shield and as a conductor for the neutral return current. Their cross sectional area must be sized in order to function as the neutral conductor.

      Cables with PVC Insulation: The inner conducting layer consists of PVC compound having high carbon black content. For the outer conducting layer, a cover of conducting tapes is preferred.

      Cables with PE or XLPE Insulation: Because of higher sensistivity to partial discharge the reliable well adhesive gap and cavity free bonding to conducting layers is of greatest significance. The inner conducting layer consists of polymer compound made conductive by adding carbon black. And the outer conducting layer is formed by semi-conducting compound along with semi-conducting tapes.

    16. Question 16. What Are Different Types Of Insulating Material?

      Answer :

      Insulation is provided to electrically isolate the individual cores from one another. The applied insulation must perform adequately in the specified temperature range, and its dielectric strength should be sufficient to sustain the electrical stresses.

      Cable insulation should have:

      • High Dielectric Strength
      • Low dielectric constant
      • Good Mechanical properties
      • Resistance to Ageing
      • High temperature withstandability

      Insulating materials are classified as thermoplastic or thermoset. Thermoplastic materials lose their form upon heating. Thermoset materials maintain their form in spite of heating. Various types of insulating materials used are : PVC, XLPE, Rubber, Impregnated Paper, etc.

      Polyvinyl Chloride (PVC):

      Polyvinyl chloride (PVC or vinyl) is a thermoplastic. PVC compound is the standard insulation for cables rated at 11000 volts or less & sheathing of entire range of cables. PVC compound is a mixture of PVC resin, plasticizer, fillers, stabilizers, lubricant, pigment. The quantity and type of each ingredient determines the properties. A broad range of electrical, physical and chemical properties is possible. PVC has good electrical properties. It is tough and resistant to flame, moisture, and abrasion. Resistance to ozone, acids, alkalis, alcohol, and most solvents is also adequate. PVC can be made resistant to oils and gasoline.

      PVC has the disadvantage of having a high dielectric constant and dissipation factor. Also plasticizer loss can cause hardening and cracking.

      Crosslinked Polyethylene:

      Crosslinked polyethylene (XLPE) is a thermoset. It is produced by compounding PE (polyethylene) with a crosslinking agent, like organic peroxide. The molecules of polyethylene are “crosslinked”, forming an interconnected network. The terms “cured” and “vulcanised” are also used for “crosslinked“.

      Elastomer:

      Elastomeric material are used for insulation and for sheaths. They are applied mainly where the product has to be particular flexible. A wide range of elastomers is nowadays available to the cable industry. This makes possible the manufacture of compounds with specific properties, such as abrasion and oil resistance, weather and heat resistance and flame resistance, combined with good overall electrical and mechanical charateristics.

      The classical elastomeric material, natural rubber, has declined in significance in recent years. In its place, the synthetic elastomers produced by the co-polymerisation of ethylene and propylene, are constantly finding new areas of application in cable engineering. This co-polymers, are generally known as EPR.

      Rubber was the first insulant to be used in Electric cable manufacture but gave way to other insulants like paper, PVC, XLPE etc. Rubber is still considered the preferred insulation for flexible cables and cables where very small bending diameter is desired.

      Paper:

      Paper tapes of specific thickness and suitable widths are lapped around the conductor. The thickness of built up insulation depends on the rated voltage of the cable. Paper insulated cores are dried and impregnated using mass impregnating non-draining compound.

    17. Question 17. What Are The Different Types Of Conductor?

      Answer :

      Conductors are divided into different classes , the flexibility of the conductor increases with the class number.

      These are as follows:

      • Cables for fixed installations: classes 1 and 2
      • The flexibles: classes 5 and 6

      Solid Conductor (Class 1):

      The conductor consists of single wire of plain or tinned annealed Copper and its cross-section is circular. Solid Aluminium conductor of sizes 1.5 mm2 , up to and including 16 mm2 is of circular cross-section. Sizes 25 mm2 and above may be either circular or shaped cross-section.

      Stranded Circular Non-Compacted Conductors ( Class 2 ):

      The conductor consists of plain or tinned annealed Copper or plain Aluminium. The number of wires in the conductor are not less than the appropriate minimum number as specified in the standards.

      Stranded Compacted Circular Conductors and Shaped Conductors (Class 2):

      The conductor consists of plain or tinned annealed Copper or plain Aluminium. The number of wires in the conductor are not less than the appropriate minimum number as specified in the standards.

      Flexible Conductors(Classes 5 and 6 ):

      Conductor consists of plain or tinned annealed Copper. The diameter of the wires in any conductor does not exceed the appropriate maximum value as given in the standards.

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