Suppliers, Distributors and Exporters of Low Tension PVC Cables

Low voltage cables are most widely used among all cables. Low voltage power cables are used in electric power distribution and control cables carry signals from electrical devices, switchgears, etc to control room. LT Cables or Low Tension PVC Cables are defined as per IS 1554 Part I having voltage grade up to 3.3kv. Cables of similar voltage range are also defined as LV Cables or Low Voltage Cables as per IEC-60502 part 1 and BS-6004

PVC insulated cables are generally manufactured up to 1000 sqmm(Single Core) and 630sqmm(Multi Core) conforming to IS, IEC & BS standards.

PVC insulated cables are suitable for use on AC single phase or three phase (earthed or unearthed ) systems for rated voltage upto and including 1100 volts. These cables can be used on DC systems for rated voltage up to and including 1500 volts to earth.

Advantages of PVC Cables

• A non-hygroscopic insulation almost unaffected by moisture.
• Non-migration of compound permitting vertical installation.
• Complete protection against most forms of electrolytic and chemical corrosion.
• A tough and resilient sheath with excellent fire resisting qualities.
• Good ageing characteristics.
• Not affected by vibration.

General Construction - LT PVC Power & Control Cables upto 1.1 KV

Conductor

The most acceptable metals for conductors are copper and aluminium due to their higher conductivity and ductility.

As copper has got higher affinity for sulphur, it corrodes in the atmosphere where sulphur fumes are present. In these conditions tinned copper should be used. Aluminium oxide film which is always present on Aluminium conductor surface acts as barrier and it protects the Aluminium conductor from corrosion in fumes laden atmosphere.

The following types of conductor construction is used in manufacture of LT cables

Insulation

The PVC covering over conductor is called insulation and is provided by extrusion process only. The insulated conductor is called core.

I.S. 1554 permits two types of PVC insulation as follows:

• Insulation with TYPE A PVC compound as per I.S. 5831 which is suitable for 70°C continuous operation.
• Insulation with TYPE C PVC compound as per I.S. 5831 which is suitable for 85°C continuous operation.

Laying Up

The cores are laid up with suitable lay. The final layer always has a right hand lay i.e. if you look along the cable, the cores move to your right hand.

Innersheath

Inner sheath of PVC either extruded / tape is provided over the overall shield as a bedding for the armour.

I.S. 1554 permits following methods of applying the innersheath of any thermoplastic material i.e. PVC, Polyethylene, etc.

Armouring

In case of armoured cables, generally galvanized steel wire / strip armouring is provided over the innersheath in multicore cables and Aluminium Round Wire or Aluminium Strip over the insulation in single core cables. It provides mechanical protection to inside cores and it carries earth return current in case of a short circuit of a core with armour.

As per I.S.1554 (Part I) round wire armouring is provided in cable, where calculated diameter under armour is upto 13 mm. Above this the armouring is either with round wire or strip of size 4 mm X 0.80 mm.

In mines, the resistance of the armour in no case should exceed the resistance of the main core by more than 33% for safety reasons. To achieve this, sometimes tinned hard drawn copper wires are required to be used along with galvanized steel wires. Sometimes two layers of Round Steel Wire or Steel Strip are applied in opposite direction with barrier tape in between are provided to give extra protection.

In case of single core armoured cables for use in AC circuits, the material for armouring has to be non magnetic, as in this case the return current is not passing through the same cable and hence it will not cancel the magnetic lines produced by the current. These magnetic lines which are oscillating in case of AC current will give rise to eddy current in magnetic armouring and hence armouring will become hot, and this may lead to the failure of the cable. Generally hard drawn aluminium wires / strip are used for armouring in this case.

Outersheath

The PVC covering over the armouring in case of armoured cables and over the Innersheath in case of unarmoured cables is called outersheath. The thickness of outer sheath is generally determine as per the relevant national and international standards. Many compounds can be used as sheath material. Different grades are available to meet specific working conditions.The following factors have to be evaluated to decide the outersheath material:

• Better abrasion resistance
• Type of installation – outdoor/ indoor, direct buried.
• Possible presence of humidity, oil, chemicals etc
• Behavior in case of fire (Fire Retardant, Fire Resistance,emission of gases and smoke)
• Range of temperature
• Better weatherproof properties. It must be stable against ultraviolet rays in case of exposure to sun.
• Cost

Considering the above the most acceptable material for outer sheath is PVC compound. It has good fire resistance due to its chlorine content. It burns when the flame is applied but fire gets extinguished immediately on removal of flame.

Fire resistance of plastics is expressed by their Oxygen Index. Oxygen Index indicates the percentage of Oxygen required in air, so that the plastic will burn like a candle at room temperature. The Oxygen Index of normal PVC used in cable is 25% while that of Polyethylene is 19%. Oxygen Index decreases with the rise in temperature and at a particular temperature it will drop to 20% and will burn like a candle. This temperature in degree celsius is known as temperature Index. Temperature Index of PVC in cable is 250°C.

Over the year the size of Petrochemical, Chemical and Power plant has increased tremendously. Moreover the automation has also increased. As a result now many cable are bunched in the cable shafts and on the cable trays. In case of a fire in these cable, the fire become self-sustaining. Moreover due to burning of PVC a dense corrosive smoke is emitted which makes firefighting difficult due to poor visibility and toxic nature of the smoke. The HCL content of smoke not only damages other nearby costly equipment but also penetrates the RCC structure and corrodes its steel reinforcement due to this there is an extensive damage to the human life and property.

To overcome these deficiencies of PVC sheath, FR (Fire Retardant) PVC compound having a minimum Oxygen Index of 29% was developed, by adding Antimony Trioxide at compounding stage. FR PVC is preferred in Petroleum and Petro Chemical Plant which are open to the sky. FRLS (Fire Retardant Low Smoke) PVC compound is a further development where Aluminium Trihydrate (ATH) and some chemical are added at compounding stage to increase the Fire Resistance of the PVC and to decrease the smoke emission and toxicity of smoke. But again this is a PVC compound and hence toxic black smoke cannot be eliminated completely.

Zero Halogen Fire Retardant (ZHFR) Compound

As discussed above, PVC has got better fire resistance due to its chlorine (Halogen) Content but it creates other problem during fire. To overcome these deficiencies ZHFR compounds were developed. Here Polyethylene or Ethylene Vinyl Acetate (EVA) plastics which are having zero halogen are imparted fire resistance properties by compounding them with certain chemicals. These materials when burn, emit little nontoxic smoke. This is the most preferred sheathing compound for underground Metros, Stations, Airports, Theatres, and Hospitals etc where human density is more.

Polyethylene Outersheath

Due to poor abrasion and fire resistance Polyethylene sheaths are generally not used. Moreover minimum 2.5% carbon black content is required in Polyethylene to prevent its degradation due to ultra violet rays when exposed to sunlight. It is mainly used where better chemical and water resistance are required.

Nylon & Polyurethane Sheaths

These plastics have better abrasion resistance and are used when there are specific requirement.

Colour of Outersheath

By default it is black as it imparts weatherproof properties. In case of cable used for intrinsically safe systems blue sheath is provided. Sometimes the clients specify Grey or Red sheath to differentiate the instrumentation cable from the normal cables.

Cable Code

The following codes are used for designating the cables.

Examples

• YWY means copper conductor, PVC insulated, round wire armoured, PVC sheathed cable
• AYFY means aluminium conductor, PVC insulated, Flat Strip Armoured. PVC sheathed cables

Due to the massive daily use of society in terms of electrical equipment’s in residential areas and commercial and industrial places the demand of electric power cables has grown consistently in the last decades

LT Cables designed to be used underground directly, buried in ducts, trenches or in tunnels for electric power transmission, are used in many applications including:

• Infrastructure
• Industries
• Power Generation
• Automation
• Lighting
• Sound and security
• Video surveillance
• Fire alarm
• Some LT cables with Special Fire Properties are used in Oil, Gas and Petroleum Sector and in application areas where fire safety is of critical importance.

Contact us for more information on Low Tension PVC Cables or to discuss your requirements. Enquiries are solicited for India, UAE and Africa on following Email id web@aakashpower.com