Interview Questions.

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

Answer :

Conductor:Conductor is a modern carrying element made of Aluminium or Copper with a selected go phase for the assigned rating, having resistance / km within certain exact limits.

Electrical Insulation (dielectric): Insulation is supplied over the conductors to electrically isolate them from each other. Various varieties of insulating materials used are : PVC, XLPE (Cross Linked Polyethylene), Rubber, and so on.

An insulated conductor is termed as Core. A cable might also have one or more cores. In a more than one core cable , the cores are helically stranded collectively. In dual, 3 & multi-core cables, the cores are laid up collectively with a appropriate lay; the outer most layer has right-hand lay and the successive layers are laid with opposite lay path.

Inner sheath (bedding): Cables with stranded cores are furnished with Inner Sheath implemented both by using extrusion or by means of wrapping. It is ensured that the form is as circular as possible. Inner Sheath is so applied that it fits closely at 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 totally on calculated diameter over laid-up cores.

Armour: A cord, strip or a tape applied helically over the cable, to guard the cable from penetration by means of sharp objects, crushing forces, and damage from rodents or dull insects, is called as Armour.

Armour is implemented over the insulation in case of unmarried center cables & over inner sheath in case of dual, 3 & multi middle cables.

Outer Sheath: Outer sheath /Jacket is normally an extruded plastic cover over the laid-up or armoured center. PVC is a not unusual sheathing cloth. Outer sheath presents mechanical, thermal, chemical and environmental protection. No electric feature is assigned to Outer sheath. The colour of outer sheath is normally black.

Question 2. What Are Different Cable Types And Categories?

Answer :

Cables may be divided into big quantity of kinds primarily based on a combination of classifications as follows:

Based at the voltage ratings as low voltage, excessive voltage, more excessive voltage cables, and many others.
Based at the conductor material, Copper conductor or Aluminium conductor.
Based at the insulating cloth as PVC insulated, Rubber insulated, XLPE insulated, and so forth.
Armoured or Unarmoured cables
Based at the sheathing cloth, as PVC Sheathed, Rubber Sheathed, Lead Sheathed, Aluminium Sheathed, etc.
Based on the number of cores as single core, two center, 3 middle, 3-and-a-1/2 middle, four core, multicore, etc.
Based on the cross-phase of the conductor.
Based at the kind of conductor, strong, stranded, area fashioned, and many others.
From above it's miles obtrusive that the forms of cables will vary widely depending upon different factors concerned. To facilitate identity and description of the sort of cable it is popular practice to adopt some shape of kind designations. With these designations it becomes less difficult to deliver in some words the right sort of cable.

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Question three. Comparison Of Xlpe Cables With Pvc Cables?

Answer :

The vital distinction is the greater toughness of insulation and, specifically, the ability to face up to a good deal high temperature with out deformation because of mechanical stress. The higher bodily houses of XLPE enable the insulation thickness to be reduced and consequently average length of the cable. The non-stop temperature rating is elevated from 70°C to 90°C and the temperature for brief circuit ratings for the cable from 160°C to 250°C.

In popular, XLPE insulated cables are competitive alternative to PVC cables for commercial use and Paper insulated cables for public deliver structures.

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

Answer :

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

Potential grading and restricting of electrical fields
Conduction of price and discharge currents
To satisfy these functions, the screening commonly incorporates a aggregate of undertaking layers with steel factors.

The importance of electric pressure and the diploma of sensitivity of the insulation material towards partial discharge govern the type of screening of the insulation with accomplishing layers.

Above certain voltages, as a way of containing the electrical subject within the insulation, semiconducting displays are implemented over the conductor & insulation. Screens are supplied to achieve symmetrical dielectric fields inside the cable shape & carry present day for the duration of brief circuit. By this it's far viable to dispose of any electric discharges arising from air gaps adjoining to the insulation.

The coefficient of expansion of polyethylene & EPR is about ten times greater than that of either Copper or Aluminium, and while the conductor is at its most working temperature of ninety°C a sufficiently massive gap is shaped among the insulation and the surface of the conductor to enable electrical discharge to occur. This discharge web site & any others which can be fashioned around a conductor while conductor is bent may be eliminated with the aid of applying a semiconducting layer over the conductor. Similarly, any discharges bobbing up from air gaps between laid-up cores can be nullified through the use of a screen over the insulation.

During the early 1960s semiconducting tapes have been carried out the conductor but those have considering the fact that been outmoded by using an extruded layer. This has the benefit of imparting each a smoother end and, because it fills the interstices between the wires, a circular envelop across the conductor. By lowering the awareness of the flux lines across the man or woman wires, the electrical stress round conductor is decreased by means of between 10% to 15%. The semiconducting layer is well matched with, and bonds to, the insulation and a nominal thickness of zero.7 mm is regular.

Question five. What Is Frls H Cable?

Answer :

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

Special functions

Reduced flame propagation
Low smoke emission
Low acid fuel technology
Formulation for the FRLS compounds, which might be specifically for the sheathing materials, require unique elements. These cables can also have insulation of PVC or XLPE, however sheath is PVC based totally, certainly compounded to fulfill FRLS H necessities.

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Question 6. What Are The General Packing Practices Followed?

Answer :

Cables are normally acquired on timber/metal drum. There is an arrow painted on the flanges of the drum which suggest the direction in which the drum must be rolled. The cable will unwind and grow to be free if the drum is rolled inside the contrary route. All drums should be stored in the sort of way as to depart enough space among them for air circulation. In no case must the drums be saved ‘ at the flat’ i.E. With flange horizontal.

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

Answer :

Conductor is a cutting-edge carrying element made up of Aluminium or Copper with a selected pass phase for the assigned score, having resistance / km inside sure distinctive limits.

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

Answer :

Conductor choice depends on numerous parameters like contemporary carrying capacity , device voltage, voltage drop, flexibility, form, and economics.

The most commonly used metals are Copper and Aluminium.

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

                       R= þ x l / A

Where

þ= Resistivity of the conductor material.

L= Length of conductor.

A = move sectional location of conductor.

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

Answer :

Double compression glands provide more assist to the heavy armored cables coming into or exiting the panel at the same time as single compression glands are used for mild armored cables.
Normal Cable Gland is also known as Single Compression Cable Gland. As the name indicates, while you tighten the gland, the grip or compression is effected only at one p [lace (i.E.) on the cable armour handiest. There is scope for moisture and corrosive vapour to enter the gland and hence into the cable.
Whereas in Double-Compression Gland, the compression takes place both on the cable armour in addition to on the inner sheath. This is type of two sealing. Hence, probabilities of moisture or vapour access are minimized. Hence those glands are also known as Weather-evidence cable glands or Flame-evidence cable glands.
The basic difference between unmarried and double compression is in Single comp there no cone and cone ring.
The mechanical guide for the cable is simplest Neoprene rubber seal, When you tighten the cable.
In double camp gland the mechanical guide to the cable most effective cone and cone ring. When we're 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 idea of area type. Those who're affiliated with oil and gas sector they will without problems apprehend about location type.
In sector 0 in which the presence of hydrocarbon is obvious (IIC) double compression gland is used because the flame course in case of double compression gland is a whole lot more than in case of unmarried compression gland.
The good judgment at the back of this is that if there may be any explosion inside the terminal field of the motor no flame should be able to come out through the cable gland with a purpose to save you hearth dangers however in which there may be no presence of hydrocarbons i.E. No risk of hearth risks (IIA/ IIB) unmarried compression glands are used.
It has nothing to do with mechanical electricity. Even in case of lighting fixtures used in IIC area double compression glands are used.
Question eleven. 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
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Question 12. What Are The Type Of Cable And How The Gland To Be Used?

Answer :

Unarmored: Unarmored Cable would require outer seal inside Gland to not simplest Provide ingress safety however also degree of retention.

Armored: Gland that required clamping mechanism to terminate the armored each robotically and electrically.

The Gland will generally be required to offer ingress safety through sealing outer sheath and retention by way of clamping amour.

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Question 13. What Is Cable Gland?

Answer :

A device designed to allow the entry of cable in to electrical device which offers sealing, retention and ear issue, bonding, grounding, insulation, strain relief or aggregate of these types of. Gland have to maintain standard integrity of enclosure in to which it's miles to be fitted.

Question 14. How To Select The Cable Gland?

Answer :

Gland need to be decided on on following Points:

Type of Cable
Gland Size
Entry Type/Thread Specification of software
Ingress Protection required.
Material
Question 15. What Is The Function Of Conductor / Insulation Screen And Material Used?

Answer :

Function of Conductor / Insulation Screen:

The conductor guard is a layer of semi-accomplishing fabric. Semi-conducting materials do not conduct strength properly sufficient to be a conductor however will not hold back voltage.

It “smoothes” out the surface irregularities of the conductor. The conductor protect makes the voltage at the interior of the insulation the same. Industry specifications define the performance of conductor defend. Good insulation shields are extruded in tandem with the insulation.

The insulation defend includes two components. These components are the extruded (auxiliary) defend and the metallic (primary) protect.

The extruded guard consist of a semi-accomplishing layer similar to the conductor guard. It makes the voltage at the outdoor of the insulation the equal.

The primary defend can consist of steel tape, drain wires or concentric impartial (CN) wires. Grounding the primary protect makes the voltage on the outdoor of the insulation floor. The Copper of the protect is typically naked, but may be coated with lead or tin. Some number one shields consists of drain wires and tape. Aluminium and lead also can be used as the protect.

Concentric neutral wires serve a two-fold reason. They function because the metal issue of the insulation defend and as a conductor for the impartial go back current. Their go sectional region must be sized if you want to function as the impartial conductor.

Cables with PVC Insulation: The inner carrying out layer consists of PVC compound having high carbon black content material. For the outer engaging in layer, a cowl of accomplishing tapes is favored.

Cables with PE or XLPE Insulation: Because of higher sensistivity to partial discharge the dependable nicely adhesive hole and hollow space unfastened bonding to conducting layers is of greatest significance. The internal carrying out layer consists of polymer compound made conductive by way of adding carbon black. And the outer engaging in layer is formed by using semi-carrying out compound at the side of semi-accomplishing tapes.

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Question sixteen. What Are Different Types Of Insulating Material?

Answer :

Insulation is furnished to electrically isolate the person cores from each other. The carried out insulation have to carry out competently within the distinct temperature variety, and its dielectric electricity have to be sufficient to sustain the electric stresses.

Cable insulation need to have:

High Dielectric Strength
Low dielectric consistent
Good Mechanical homes
Resistance to Ageing
High temperature withstandability
Insulating substances are categorized as thermoplastic or thermoset. Thermoplastic materials lose their shape upon heating. Thermoset substances hold their form in spite of heating. Various sorts of insulating substances used are : PVC, XLPE, Rubber, Impregnated Paper, and so forth.

Polyvinyl Chloride (PVC):

Polyvinyl chloride (PVC or vinyl) is a thermoplastic. PVC compound is the same old insulation for cables rated at 11000 volts or much less & sheathing of entire range of cables. PVC compound is a mixture of PVC resin, plasticizer, fillers, stabilizers, lubricant, pigment. The quantity and kind of every aspect determines the houses. A huge range of electrical, physical and chemical properties is viable. PVC has precise electrical houses. It is difficult and resistant to flame, moisture, and abrasion. Resistance to ozone, acids, alkalis, alcohol, and maximum solvents is also adequate. PVC may be made resistant to oils and gasoline.

PVC has the downside of getting a high dielectric steady and dissipation factor. Also plasticizer loss can purpose hardening and cracking.

Crosslinked Polyethylene:

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

Elastomer:

Elastomeric cloth are used for insulation and for sheaths. They are applied mainly wherein the product has to be specific flexible. A extensive variety of elastomers is in recent times available to the cable enterprise. This makes possible the manufacture of compounds with particular properties, including abrasion and oil resistance, climate and warmth resistance and flame resistance, blended with exact average electrical and mechanical charateristics.

The classical elastomeric fabric, natural rubber, has declined in importance in recent years. In its place, the synthetic elastomers produced with the aid of the co-polymerisation of ethylene and propylene, are continuously finding new regions of application in cable engineering. This co-polymers, are generally referred to as EPR.

Rubber become the first insulant to be used in Electric cable manufacture however gave manner to different insulants like paper, PVC, XLPE and so forth. Rubber remains taken into consideration the preferred insulation for bendy cables and cables where very small bending diameter is favored.

Paper:

Paper tapes of unique thickness and appropriate widths are lapped across the conductor. The thickness of constructed up insulation relies upon at the rated voltage of the cable. Paper insulated cores are dried and impregnated the use of mass impregnating non-draining compound.

Question 17. What Are The Different Types Of Conductor?

Answer :

Conductors are divided into distinct training , the flexibility of the conductor will increase with the magnificence number.

These are as follows:

Cables for fixed installations: training 1 and a couple of
The flexibles: training five and six
Solid Conductor (Class 1):

The conductor includes unmarried cord of undeniable or tinned annealed Copper and its cross-phase is round. Solid Aluminium conductor of sizes 1.Five mm2 , up to and along with 16 mm2 is of round go-section. Sizes 25 mm2 and above may be either circular or shaped go-section.

Stranded Circular Non-Compacted Conductors ( Class 2 ):

The conductor consists of simple or tinned annealed Copper or undeniable Aluminium. The variety of wires within the conductor aren't much less than the suitable minimal variety as distinctive inside the requirements.

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

The conductor consists of simple or tinned annealed Copper or undeniable Aluminium. The range of wires in the conductor aren't much less than an appropriate minimum number as certain in the requirements.

Flexible Conductors(Classes 5 and six ):

Conductor includes simple or tinned annealed Copper. The diameter of the wires in any conductor does not exceed the precise maximum cost as given in the standards.

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