ALL ABOUT PVC CABLES EASY EXPLANATION103

PVC CABLES: INSULATED (HEAVY DUTY) ELECTRIC CABLES

These PVC cables are generally used up to & including 11 kV installations. The insulation material used is polyvinyl chloride (PVC) and conductors are made from electrical-grade aluminum or copper. To give flexibility, the conductors of PVC cables are stranded. The PVC cables are used where a combination of ambient temperature and temperature rise due to load results in a conductor temperature not exceeding 70°C under normal operation and 160°C under short circuit conditions.

Core Identification

Different cores in a PVC cable are identified by the colours of PVC insulation. Accepted colour codes for PVC cables are as follows.

• Single core: Red, yellow, blue, or black.
• Twin core: Red and black
• Three cores: Red, yellow, and blue.
• Four cores: Red, yellow, blue, and black.
• Five core: Red, yellow, blue, black, and grey.

In 3.5-core PVC cables, there are three main cores are colored red, yellow, and blue to represent the three phases R, Y, and B respectively, and the reduced core is colored black which indicates the neutral N.

For PVC cables of voltage grade up to and including 6.6 kV, the method of core identification shall be as follows:

• Different colouring of the PVC insulation or
• Colored strips applied on the cores or
• By numerals (1,2,3), either application the numbered strips or printing the numbers on the cores.

For PVC cables of voltage grade of 6.35/11 kV, the method of core identification shall be as follows:

• Colored strips applied on the cores or
• By numerals (1,2,3), either application the numbered strips or printing the numbers on the cores.

Ratings and Applications

PVC insulated power cables are designed and manufactured in a voltage rating ranging from 650/1100 volts up to and including 6.35/11 kV and the number of cores are 1, 2, 3, 3.5, 4, or 5 cores. The nominal area of aluminum conductors for single-core cables ranges from 1.5 to 1000 sq. mm and from 2.5 to 630 sq. mm for multicore cables.

PVC unarmoured single-core and multicore cables are particularly useful for the delivery of power to various equipment in power stations, substations, house service connections, street lighting, building wiring, etc. They can be installed indoors or outdoors, in the air, or in cable ducts.

PVC armored single-core and multicore cables are useful for the power delivery in power generating stations, power transmission substations, distribution systems, street lighting, industrial installations, etc. The armouring of these cables can withstand forces due to rough installation, operating conditions, and various stresses. They can be laid in water or buried directly in the ground even on steep slopes.

TYPE OF INSULATION

Type A

General purpose insulation for maximum rated conductor temperature 70°C intended for cables with rated voltages U₀/U up to and including 3.3/3.3 kV.

Type B

General purpose insulation for maximum rated conductor temperature 7O°C intended for cables with rated voltages U₀/U above 3.3/3.3 kV.

Type C

Heat resisting insulation for maximum rated conductor temperature 85°C intended for cables with rated voltages up to and including 1100 volts.

CLASSIFICATION OF CONDUCTORS USED IN PVC CABLES

The conductors of PVC cable in various classes are discussed below:

• Cables for fixed installations Classes 1 and 2
• The Flexibles Classes 5 and 6
• Copper welding cables Class 6

Aluminum conductors for welding cables have not been assigned any class number.

Solid Conductor (Class 1)

The conductor shall consist of a single wire of plain or tinned annealed copper or plain aluminum. The solid copper conductor shall be of circular cross-section. Solid aluminum conductors of sizes from 10 mm² up to and including 35 mm² shall be of circular cross-section. Sizes above 35 mm² may be of either circular or shaped cross-section.

Stranded Circular Non-Compacted Conductors (Class 2)

The conductor shall consist of plain or tinned annealed copper or plain aluminum. The wires in the conductor shall have the same nominal diameter before the stranding process.

Stranded and Compact Circular Conductors and Shaped Conductors (Class 2)

The conductor shall consist of plain or tinned annealed copper or plain aluminum. The ratio of the diameters of two wires before stranding in the same conductor must be less than 2.

Flexible Conductors (Classes 5 and 6)

The conductor shall consist of plain or tinned annealed copper. The wires in the conductor shall have the same nominal diameter before bunching.

Flexible Aluminum Conductors for Welding Cables

The conductor shall consist of plain aluminum. The conductor wires must have the same nominal diameter before stranding.

TYPE OF SEATHS

Seaths are an external layer of protection made up of mostly PVC intended to provide protection to the inner conductors. Types of seaths are discussed in brief below:

Type ST1

General purpose sheath intended for use in cables operating at a maximum rated conductor temperature of 70°C.

Type ST2

Heat-resisting sheath intended for use in cables operating at a maximum rated conductor temperature of 90°C.

Type of Armour

Galvanized round steel wires are used as armours , where the calculated diameter below armouring does not exceed 13 mm.

Galvanized round steel wires or galvanized steel strips are used as armours, where the calculated diameter below armouring is greater than 13 mm.

Application of armour is done over the insulation in the case of single-core cables and over the inner sheath in the case of multicore PVC cables.

In the case of single-core cables for use on A.C. power systems, the armouring material shall be of a non-magnetic type.

A cross-sectional view of some of the PVC insulated cables is given below:

PVC insulated and PVC sheathed, low voltage unarmoured multi-core cable:

PVC insulated and PVC sheathed, low voltage armoured single core cable:

PVC insulated and PVC sheathed, low voltage armoured multi-core cable:

PVC insulated and PVC sheathed, medium voltage three-core cable

CROSS-SECTIONAL AREA OF REDUCED CONDUCTOR