Low Voltage Electric Cables Paul Chaplin Proud to be an Australian - - PowerPoint PPT Presentation

Low Voltage Electric Cables

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Paul Chaplin Proud to be an Australian Family Business Owner Switches Plus Components

Electric Cables are not just Electric Cables

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Electric Cable Construction

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Electrical Conductors

A conductor is an object or type of material that allows the flow of an electrical current in one or more directions. Materials include Copper, Aluminium, Gold, Silver.

• Electrolytic-Tough-Pitch (ETP) is the most common copper used for electrical applications.

ETP is required to be 99.9% pure. To go to 99.99% pure copper is more expensive and provides at best a 1% increase in conductivity.

• When metal is cold worked or formed, it becomes work hardened, or strain hardened.

Copper conductors go through a considerable amount of work hardening as the copper rod is drawn down through ever decreasing die sizes until the required conductor dimension is

• achieved. Copper in this state is known as hard drawn copper.
• Hard drawn copper is difficult to work with. The stranding and bunching of the finer wires in

this state would be very difficult. By heat treating the copper at the correct temperatures the ductility can be restored to make the copper soft and flexible again. This heat treating process is known as annealing and the resulting metal is known as soft annealed copper. The degree of annealing is controlled by temperature and time, copper wire is used with different degrees of annealing depending on the application.

• Hard drawn copper has a significantly higher tensile strength than soft annealed copper and

is used as overhead wire whereas the soft annealed copper is flexible and has somewhat improved conductivity over hard drawn copper conductor.

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Operating Temperatures of Electric Cable

The operating temperature of an electrical cable normally refers to the minimum and maximum temperature that the cable can safely operate at for a sustained period of time. This operating temperature is determined by the insulation and/or sheathing material around the cable.

• Each material type will have an upper and lower range of temperatures

within which it continues to be suitable for use. This varies widely depending on the material type as well as whether or not the cable is required to be flexible at these temperatures. Generally, materials soften at higher temperatures and become rigid at lower temperatures making the material less suitable for applications involving flexing at either low or high temperatures.

• A typical PVC insulation material has a temperature range of -15°C to 70°C

for applications. Silicone rubber typically has a temperature range of -60°C to 180°C for fixed applications

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Life Expectancy of Electric Cables

There are many different environmental and operational conditions which are likely to influence the longevity of electrical cables in service.

• The insulation and sheathing materials of cables will degrade over time

when exposed to heat, UV light, ozone, various chemicals, excessive flexing, or mechanical action, not to mention in certain situations cables may be exposed to attack by termites, birds and rodents.

• When a current passes through the cable conductor it generates heat - the

higher the current the more heat will be generated. This will have a significant impact if the conductor is undersized or continuously at or near the cable’s maximum permissible resistance or rated load, degrading the insulation and sheathing materials over time until they become dangerous and require replacement.

• Although it is primarily the condition of the insulation and sheathing

materials rather than the actual conductors that determine the longevity

• f the cables, water ingress and poor fixings can also cause corrosion and

damage.

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Electrical Insulating materials - Properties of Thermal Endurance.

better known as “useful lifespan”

IEC 60216 -1 page 11 Introduction

• The listing of the thermal capabilities of electrical insulating materials, based on

service experience, was found to be impractical, owing to the rapid development of polymer and insulation technologies and the long time necessary to acquire appropriate service experience. Accelerated ageing and test procedures were therefore required to obtain the necessary information. The IEC 60216 series has been developed to formalize these procedures and the interpretation of their results.

• Physical-chemical models postulated for the ageing processes led to the almost

universal assumption of the Arrhenius equations to describe the rate of ageing. Out

• f this arose the concept of the temperature index (TI) as a single-point

characteristic based upon accelerated ageing data. This is the numerical value of the temperature in °C at which the time taken for deterioration of a selected property to reach an accepted end-point is that specified (usually 20,000 h).

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Common cable insulating materials operating temperature defined by the IEC60216 test method

• PVC

= 75°C

• XLPE

= 90°C

• EPR, CPE, CSP, Rubbers

= 90°C

• Silicon Rubber

= 180°C Cable insulation degradation caused by thermal aging

Electrical Insulating materials - Properties of Thermal Endurance.

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Understanding why PVC is rated at 70°C and why XLPE is rated at 90°C we now better understand why AS/NZS3008-1-1:2017 calculate current ratings for PVC based on a 70°C conductor temperature and for XLPE/EPR based on a 90°C conductor temperature: Perhaps what is not highlighted by this standard is that the elongation reduction to 50% absolute is calculated on 20,000 hours exposure time at this temperature (which is only 2.3 years). In fact this standard does not really expect engineers to use the cables at (PVC) 70°C

• r (XLPE) 90°C continuously or the cable lifespan will be exceptionally short. They assume

usage will be on a basis of discontinuous loading where it is not anticipated the cables will be fully loaded 100% of the time. This pragmatic approach is the only way polymeric cable insulations can be economically viable. A common ‘rule of thumb’ for cable polymer insulation aging is that a reduction of 10°C in the average cable operating temperature across its life span will double the insulation life time to the 50%EB (Elongation at Break) point: i.e:

Electrical Insulating materials - Properties of Thermal Endurance.

AS/NZS 3008.1/1:2017 Cl 3.5.6 states : The ratings given are for continuous loading. The question that needs to be asked is “How long is continuous ?”

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Thermoplastic V 75-PVC / TPE-7 operated continuously at: 75°C will degrade to 50%EB in 20,000 hours (2.3 yrs) 65°C will degrade to 50%EB in 40,000 hours (4.6 yrs) 55°C will degrade to 50%EB in 80,000 hours (9.2 yrs) 45°C will degrade to 50%EB in 160,000 hours (18.4 yrs) XLPE 90, R-EP 90, CPE/CSP-90 operated continuously at: 90°C will degrade to 50%EB in 20,000 hours (2.3 yrs) 80°C will degrade to 50%EB in 40,000 hours (4.6 yrs) 70°C will degrade to 50%EB in 80,000 hours (9.2 yrs) 60°C will degrade to 50%EB in 160,000 hours (18.4 yrs)

NOTE: a 50% EB represents a reduction in the materials original property of ≈80%

Electrical Insulating materials - Properties of Thermal Endurance.

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Bending Radius of Electric Cables

The cable bending radius is a measurement of the smallest radius a cable can be bent around without damaging the cable.

• Factors which influence the minimum bending radius include the cable size,

the cable construction, the conductor type and the sheathing and insulation types used.

• The bending radius is normally expressed as a factor of the overall dimension
• f the cable for example, 6D or 6x the outer diameter of the cable.
• The cable manufacturer will determine a minimum bending radius so as to

protect the integrity and performance of the cable. Where the cable bending radius has been exceeded during installation - the cable can show kinking or

• ther sheath damage as an indication of other possible problems such as hot

spots, which combined with over-stressed insulation and sheath may result in premature ageing and potential cable failure.

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Impedance in Electric Cables

• Impedance is measured in Ohms and represents the total resistance that

the cable presents to the electrical current passing through it. Impedance is associated with AC circuits.

• At low frequencies the impedance is largely a function of the conductor

size (resistance), but at high frequencies, conductor size, insulation material and insulation thickness all affect the cable's impedance. Matching impedance is very important, for example, if the system is designed to be 100 Ohms, then the cable should match that impedance,

• therwise error-producing reflections are created at the impedance

mismatch, seen as lower return loss in bidirectional signal cables.

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Capacitance in Electric Cables

• Two conductors which are separated by a distance can store an electric charge between
• them. A cable with two or more wires can also store a charge, and this can affect the way the

cable performs. Capacitance describes the ability of two conductors, separated by an insulating material, to store charge. Capacitance in cables is usually measured in pf/m (pico farads per meter) The lower the capacitance the better the cable performance.

• Capacitance is a particular problem with data or signal cables. When a voltage signal is

transmitted through a twisted pair or a coaxial type cable, a charge builds up across the insulation between the conductors. The charge that builds up in the cable over a period of time is due to the inherent capacitance this results in a delay causing interference in the signal transmission. Digital data pulses which are square in shape are transformed to form a shape similar to “saw teeth” due to the ramp up and discharge, this may result in the circuitry failing to recognise the digital pulses. There are a number of ways to reduce the capacitance in cable design including:

• Increase the insulation thickness
• Decrease the conductor diameter
• Use an insulation with a lower dielectric constant
• Usually a combination of all three is used as either method has its limitations.
• Having a metallic shield over the cable introduces a further capacitance, that of core to

shield, which can significantly increase the overall capacitance of the cable.

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Attenuation in Electric Cables

Attenuation is generally associated with data cables and refers to any reduction in signal loss, calculated as a ratio of the power input signal to

• utput signal, which is measured in decibels per unit length (db/ft).

Attenuation is very dependent on signal frequency, a cable that performs very well with low frequency data may demonstrate poor performance at higher data rates, cables with lower attenuation provide improved performance. Attenuation occurs on computer networks for several reasons including:

• Range for wireless or length of run for wired networks
• Interference from other networks or physical obstructions for wireless

systems

• Wire size, thicker wires are better.

Reducing attenuation in an electrical system and improving performance can be achieved by increasing the power of a signal through a signal amplifier or repeaters.

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Braiding of Electric Cables

Cables are braided for one of two reasons, either to electrostatically screen the cable or to provide mechanical strength to the cable.

• Applying a braid of metallic wires in the cable’s construction to achieve

electrostatic screening and/or mechanical strength as opposed to applying metal tapes is that the braiding maintains the cables flexibility. The design of the crossing, interwoven wires allows for bending and stretching of the braiding without buckling, folding or kinking in the way the tapes might do as a result of a flexible application.

• Where the braiding is designed to provide an electrostatic screen to ensure

signal integrity it is composed of an excellent electrical conductor such as copper, tinned copper or aluminium. If the braiding is designed to provide mechanical strength or toughness it can be composed of a number of different materials, such as steel wires, nylon strands or glass fibres.

• When applied as a covering to the cable a braid can also serve to provide

increased protection against hot surfaces, offering resistance to abrasion and cutting, or helping prevent attack by rodents and birds.

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Insulation resistance testing is a key test for electrical cables as it is a measure

• f how effectively the cable is insulated. Poor insulation may result in short

circuit, electric shock or fire. Cable insulation tests are conducted to test the insulation at the cable's maximum operating temperature. This maximum operating temperature is defined by the material types used in insulation and sheathing. At temperatures over-and-above this maximum operating temperature the material will not be suitable for continuous operation and will eventually break down causing premature cable failure.

Insulation Resistance Testing of electric Cables

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Thermoplastic & Thermoset Insulation for Electric Cables

Plastic or polymers used in cable insulation are either thermoplastic or thermoset.

• Thermoplastic material is softened by heating and can be shaped, with the shape then

maintained by cooling. The important characteristic of thermoplastic material is that this process can be repeated with the material re-softened and reshaped over and over. Thermoplastic materials can be easily recycled. Thermoplastic types commonly used are PVC (Polyvinyl Chloride) and PE (Polyethylene).

• Thermoset materials are softened by heating and can be shaped and then cooled to retain a

new shape however unlike thermoplastic material, this can only be done once. This is due to a chemical reaction that has taken place during the polymerisation. Thermoset types include rubber insulations such as; silicone rubber and EVA (Ethylene-Vinyl Acetate).

• PE and PVC can be cross-linked making them thermoset types. PVC and XLPE materials once

cross-linked have enhanced resistance to temperature, improved dielectric strengths & resistance to chemicals.

• The dielectric strength of a material is a measure of the electrical strength of an insulator. It

is defined as the maximum voltage required to produce a dielectric breakdown through the material and is expressed in terms of Volts per unit thickness. The higher the dielectric strength of a material the better an electrical insulator it makes. IEC 60243 is a standard referred to for a method of testing dielectric strength of a material

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The Benefits of PVC Insulated electric Cables

PVC (Polyvinyl chloride) is widely used in electrical cable construction for insulation, bedding and sheathing. PVC is easy to process & recycle, cost-effective and also has excellent ageing properties and typically exceeds a 25 to 30 year service life.

• Cable with a PVC insulation or sheath is normally flame retardant, which is an important

consideration for electric cables in most applications. PVC can be made resistant to a wide range of chemicals including oils, acids and alkalis, and is tough, durable and resistant to abrasion. The addition of various additives can improve its temperature range, typically from -40 to 105°C, as well as the resistance to sunlight, reduced smoke emission and improved water resistance.

• As an insulation material cables often come down to a choice between XLPE or PVC (a

thermoplastic and a thermoset material). There are thermoset versions of PVC which are cross-linked, typically with electron beam technology but they are more expensive to use and so when specified they are typically in high-spec applications in industries such as public infrastructure, defence and automotive. Thermoset or cross-linked PVC has an improved temperature resistance, is tougher, and has a better dielectric strength, which means that a thinner coating or insulation layer can be applied making the overall cable dimension smaller.

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The Benefits of PE Insulated Electric Cables

Polyethylene (PE) is a semi-crystalline polymer available in a wide variety of versions with differing chemical structures, molecular weights and densities determined by the various methods of polymerisation.

• PE has excellent dielectrics – high dielectric strength, low dielectric constant, and

low dissipation factor at all frequencies. This makes it an ideal insulation across a range of different cable types for shigh speed transmission, high frequency signal and in low, medium and high voltage power cables & overhead lines.

• PE naturally has a poor fire resistance but, it can be significantly improved by the

addition of fillers; both halogenated, or non halogenated types.

• PE can also be compounded to include additives which enhance other properties

such as resistance to sunlight, weathering and chemical degradation. PE is a hard and abrasion-resistant material which makes it useful as a sheathing material in various applications. Where a more flexible material is required the addition of small amount of butyl or ethylene propylene rubber (EPR) can improve flexibility. The toughness of the PE also makes it suitable for direct burial in the ground.

• The temperature range is typically -65°C to +75°C but cross-linking the polyethylene

(to make XLPE) can extend this temperature range to +90°C.

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The Benefits of XLPE Insulated electric Cables

XLPE or Cross-linked polyethylene is a thermoset insulation material. Crosslinking polymers is a process which changes the molecular structure of the polymer chains so that they are more tightly bound together. Crosslinking is done either by chemical or physical means.

• Chemical crosslinking involves the addition of chemicals or initiators such

as silane or peroxide to generate free radicals which form the crosslinking.

• Physical crosslinking involves subjecting the polymer to a high energy

source such as high-energy electron or microwave radiation.

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XLPE VS PVC electric Cable Insulation

XLPE is suitable for voltage ranges from low to extra high voltage, surpassing

• ther insulation materials such as PVC, Ethylene Propylene Rubber (EPR) and

silicone rubbers. Cross-linking the polyethylene enhances it’s chemical and oil resistance at elevated temperatures and makes it suitable for use as a Low Smoke Zero Halogen material.

• The mechanical properties of the XLPE are superior to many other

insulations, offering greater tensile strength, elongation and impact

• resistances. The addition of carbon black can be used to further enhance

hot deformation and cut through resistance. XLPE insulation will not melt or drip, even at the temperatures of soldering irons. It has increased flow resistance and improved ageing characteristics.

• Improved water-tree resistance is another benefit of XLPE insulation for LV

& MV Cables over PE insulations. Water treeing is a defect which is the result of imperfections in the insulation where fracture lines occur and grow in the direction of the electric field, increasing with electrical stress. It should be noted that this effect is not just limited to PE materials.

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The Benefits of Rubber Insulated Cables

Rubber has been used as cable insulation and sheathing materials long before other insulations such as PVC and PE. It remains widely used across industrial applications.

• All synthetic rubbers are thermoset or cross-linked by a process referred to as
• Vulcanisation. As thermoset materials they do not soften or melt when exposed to

heat.

• The properties of synthetic rubbers can be significantly changed through the addition of

various additives including fillers, vulcanising agents, accelerators, antioxidants, and antiozonants.

• Typical rubber cable compounds include Natural rubber, SBR or Styrene-Butadiene

Rubber, Butyl, Ethylene Propylene Rubber (EPR), Silicone Polychloroprene Chlorosulphonated Polyethylene (PCP) and Fluorocarbon.

• The principle advantage of all rubber cables over other insulated cables is their

excellent flexibility in a wide temperature range. They also have very good water resistance properties. Many rubber cables also have superior abrasion & weathering resistance making them particularly suitable in harsh environments as trailing leads for portable electrical appliances, power tools, pumps and generators. Rubber cables are also compounded to give excellent resistant to oils and other chemicals.

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The Benefits of PUR Sheathed Electric Cables

PUR or Polyurethane is a thermoplastic material with superior physical properties to that of even the toughest thermosetting rubber. Being thermoplastic makes it recyclable.

• PUR is not suitable as an electrical insulation material but has some outstanding

properties as a cable sheathing, making it suitable for high performance electrical cables in the most challenging of environments. It is very flexible throughout a broad temperature range, typically between -40°C and +125°C.

• PUR sheathing is extremely wear-resistant and mechanically tough, it’s very difficult to

cut or tear. It has excellent resistance against; environmental humidity, ozone, UV radiation, microbes, and a wide range of chemicals and oils. A useful characteristic of PUR as a sheathing material is its anti-kink property, ideal for any flexible or retractable cables.

• Cables sheathed with PUR are ideal for a range of applications such as sensor and

control cables, drag cables for automatic equipment, automation cables for robots and handling tools, energy cable & spiral applications as well as use in railways, airports, off shore, open cast mining and nuclear power stations.

• PUR is a low smoke halogen free material so make ideal safety cables. PUR is also

microbe resistant so are ideal for use in the food, beverage, dairy, scientific and medical industries

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The Benefits of Silicone Insulated Electric Cables

Silicone rubber insulated cables have an outstanding thermal range of up to 200oC and down to -90°C. Silicone rubber cables have excellent flexibility. Whilst silicone rubber insulation doesn’t offer the same mechanical toughness and cut-through resistance when compared to most other elastomers, this can be compensated for with the addition of a glass fibre braid and silicone varnish.

• The mineral nature of silicone rubber insulation makes themuniquely suitable for

fire resistant cables that must maintain circuit integrity in the event of a fire. When the cable is in a fire situation a film of fused silica is deposited onto the conductor providing substantial insulation properties. The addition of specialist additives can enhance the strength of this fused silica around the conductor. Silicone cables are LSZH - low smoke zero halogen materials - an additional benefit that makes them particularly suitable for fire situations.

• Silicone insulation also has good oil, solvent, ozone and weathering resistance.

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The Benefits of EPR Insulated Electric Cables

Ethylene Propylene Rubber (EPR) is a generic term for a wide range of polymers based on copolymers of ethylene and propylene. It is one of a number of rubber insulation materials. EPR polymers can be tailored for different applications.

• EPR is widely used as an insulation material due to its high dielectric strength but it is

also used as a sheathing material exhibiting excellent ozone and weathering resistance. EPR has a wide thermal range typically in the region of -55°C to 150°C. Unlike other

• rganic rubbers, the copper conductor does not need to be tinned to prevent

deterioration of the rubber.

• EPR rubber is noticeably softer than Natural rubbers and Styrene-Butadiene rubbers so

can be used as a replacement material in many applications. Where greater hardness is required, the EPR compound can be blended with polyethylene (PE) or polypropylene (PP) to achieve improved physical properties. Mechanical properties include resistance to compression, cutting, impact, tearing and abrasion.

• Although EPR does not offer a good resistance to oils, it is resistant to a wide range of
• ther chemicals including many acids, alkalis and organic solvents. It is also highly

resistant to moisture.

• Like XLPE insulation, EPR insulation is suitable for many higher voltage applications and

whilst its dielectric properties are not as good as those of XLPE it does have some important advantages over XLPE including extra flexibility, reduced thermal expansion, and low sensitivity to water treeing.

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The Benefits of PCP Insulated Electric Cables

Polychloroprene (PCP) was one of the first commercially available synthetic rubbers and is an exceptionally tough and flexible sheathing material with resistance to tears, abrasions, impact, crushing and chipping.

• PCP has a broad temperature range and doesn’t become brittle even at

temperatures as low as -40°C nor degrade at temperatures as high as 120°C. It is also suitable for even higher temperatures for brief or intermittent periods. It has very good resistance to swelling and to a wide range of chemicals including both natural oils and aliphatic hydrocarbons, making it particularly useful as a sheathing material for applications such as trailing cables used in mining, the oil & gas

• industries. It is also resistant to a range of solvents, acids and alkalis, mildew,

fungus and many other biological agents, making it ideal for use in chemical plants. As a sheathing material it provides the cable with superior weathering resistance and has proven to have excellent ageing properties in permanent outdoor applications.

• Whilst PCP doesn’t offer very good insulation properties it can be blended

with natural rubber materials to enhance the toughness. This material also has very good fire resistant properties and doesn’t support combustion.

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The Benefits of CSPE Insulated Electric Cables

CSPE stands for Chlorosulfonated polyethylene – it is also referred to as CSP.

• CSPE is a thermoset cross-linked insulation and sheathing material with excellent

electrical and physical properties. It is typically used as an insulation for cables with a voltage rating up to 600V as well as being a sheathing material for almost any type of

• cable. It has a wide temperature range from -40°C up to +148°C and can be

compounded to achieve even higher temperatures than this.

• It is resistant to cold flow - the viscous flow of a solid at ordinary temperatures due to

pressure from external loading such as clamping. Other mechanical properties include resistance to impact, abrasion, crushing and chipping. CSPE is regarded as having superior mechanical properties even amongst the other elastomers. Ideal for outdoor use, the sheathing has extremely low water absorption properties, is not effected by

• zone, and has very high resistance to ageing by both sunlight and oxidation.
• CSPE sheathed cables are favoured in processing facilities where airborne chemicals

attack ordinary-duty sheathing materials and metal conduits. It is also resistant to hydrocarbons, oils, greases and fuels and exhibits excellent fire resistant properties. It is ideal for use in mines and in oil & gas applications.

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Electrical Cables Suitable for Outdoors

• Cables for external use have been designed to survive the adverse

conditions in the outdoor environment. The outer layers of the cable must serve to protect the cable from external influences such as mechanical damage, water, extremes of temperatures, rodent, bird or insect attack, UV exposure from sunlight, and ozone in the atmosphere.

• There are a wide range of cables suitable for outdoor use. As a minimum,

they must be weather resistant, which includes protection against the typical ambient temperature range, UV light, ozone and water. PVC and Polyethylene can be made to be suitable with the addition of specific additives or stabilisers such as, carbon black.

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Electric Cables suitable for use in Water

Cables designed to be submerged in water, or in constant contact with water are usually designed to be both laterally and longitudinally

• watertight. Laterally watertight ensures that water can’t penetrate into the

cores of the cable. Longitudinally water tight cable is designed with a barrier to the spread of moisture along the cable length. Longitudinal and lateral water-tightness can be achieved in a number of ways including the use of water-blocking or water swellable tapes and water swellable powders. Lateral water tightness can also be achieved with certain water resistant rubber sheathing materials.

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Hydrocarbon Resistant Electric Cables

Hydrocarbons are organic compounds that are made of hydrogen and carbon atoms. They are notably found in crude oil and natural gas.

• Hydrocarbons are either aliphatic or aromatic types, the difference between them is

associated with the chemical bonding, with the two types reacting very differently.

• Oil can be particularly damaging to cables. Two different processes can take place,

either the plasticiser may migrate from the cable sheathing into the oil causing embrittlement and cracks in the cable sheathing. Alternatively, the oil may be absorbed by the cable sheathing and insulation materials causing swelling and softening of the material effecting their mechanical and electrical properties.

• Hydrocarbon resistant cables, also referred to as MUD resistant cables, are particularly

used in the marine industry where cables have traditionally been made with a lead sheathing layer. The sheathing material serves as a barrier to moisture ingress and is resistant to hydrocarbons and many other chemicals. It should be noted that, where used, lead has many disadvantages, including environmental concerns, weight, cost and the requirement for large bending radii.

• FEP, Fluorinated Ethylene Propylene has excellent resistance to hydrocarbons and has

been replacing lead sheathing in many applications. There are other sheathing materials used as composite or multi-layer sheathing, which may also achieve the same or similar chemical and moisture barriers to Hydrocarbons.

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Electric Cables Terminations

There are several different ways to terminate cables. The termination method will depend on the system installed, the type of cable, and the device it is being terminated to. Using the proper termination method is essential for maintaining the electrical and mechanical integrity of the cable.

• A solder type connection allows for a strong, solid mechanical and electrical connection. The solder

is applied with a soldering iron and care must be taken that this is hot enough to ensure a proper liquid flow of solder around the jointing parts.

• Crimping of terminals, lugs, links and electrical contacts are the most frequently used, and applied

by mechanical force around the conductor ends. This method is ideal for terminating solid and stranded conductors. Crimp Type terminals may also grip both the insulation and the conductor. The choice of crimp size and crimp tool is important to make sure that the cable is neither under crimped which would result in a poor or loose connection or, over crimped which would result in damage to the cable and the terminal, lug, link or electrical contact being used.

• Insulation displacement is a means of making a connection without having to cut the cable.

Connection pins are pushed through the sheath and/or the insulation and onto the conductor. This type of termination / connection is only suitable for certain types of cable.

• Direct connection using spring clamp & screw termination terminal blocks or junction blocks is

growing in poularity. This technique is ideal for solid and stranded conductors. For stranded cables a cable ferrule (boot lace ferrule) should be crimped onto the wire, to ensure a good connection is applied to all the strands of the conductor.

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Electric Cables Joints

• Cable joints are used to connect low voltage, medium and high voltage
• cables. There are several different types of jointing methods and the right

method will depend on the size, shape and configuration of the cable, the voltage rating, the structure, the insulation type, the particular application, and the number of cores to be jointed.

• The joint should provide electrical insulation and mechanical protection, it

may also need to provide a barrier to water ingress.

• The conductors may be joined by either welding, crimping, soldering or

using mechanical connectors. The jointing insulation applied over the conductors must be compatible with the cable voltage and materials and may include heat or cold shrinkable insulations, moulded types or special tapes.

• The structure of the joint will depend upon whether the intention is for a

simple straight-through connection between two cables or if there is a requirement to have a branch take-off for connections to other cables.

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Earthing & Bonding Of Electric Cables

• Earthing is a safety measure to prevent electric shock or damage to

equipment by providing a low resistance path for electric current to flow to earth in the event of a fault. For example if there is an electrical fault in an appliance such as a cook top then the fault current flows to earth through a protective conductor. A protective device such as a Circuit Breaker, Residual Current Device or a combination of both in the consumer unit switches off the electric supply to the cook top rendering it safe.

• Bonding is simply a term used for connecting together all the metallic

parts that are not supposed to be carrying electric current to the same electrical potential. This means that no electrical current can flow between these parts. The primary reason for bonding is to prevent a person getting a shock when they touch two metal pieces of equipment at different potentials. By earthing these bonded elements it protects people and equipment from harmful electrical faults.

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Protecting Cables Against Mechanical & Environmental Damage

Electrical cables are installed in a wide variety of environments and it is often necessary to provide protection for these cables to prevent mechanical and environmental damage. Some of the methods for protection include:

• Braided Sleeving: Flexible braiding such as polyamide fibres which offers

protection from heat and abrasion.

• Plastic conduit: Lightweight tubing suitable for light mechanical protection

and chemical resistance. This type of conduit is typically used in domestic applications.

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Protecting Cables Against Mechanical & Environmental Damage

• PTFE Conduits: these are used for protection against extreme conditions and offer

excellent chemical resistance, high and low temperature resistance, very good tensile and fatigue strength and resistance to fire, moisture, vibration and abrasion.

• Flexible Metal and Rigid Conduit: This is a heavier duty conduit tubing usually

galvanised to prevent corrosion. This offers significant mechanical protection and fire resistance.

• Cable ducts: Cable ducting is also a means of offering mechanical and environmental

protection to cables, ducts can be plastic, metal or concrete and can be of sufficient size to offer protection to many different cables and electrical circuits.

• Other cable accessories are available to offer protection to cables at particular points

such as in wiring panels and lighting fixtures and include edge protectors and grommets.

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