18 | Conductors & Cable

“ cable ” means a length of insulated single conductor, whether solid or stranded, or of two or more such conductors, each provided with its own insulation, which are laid together; the insulated conductor or conductors may or may not be provided with an overall covering for mechanical protection;

Component of cable

Cables consist of three major components:

conductor
insulation
protective jacket or additional insulation material on outer cable

Conductor Material

These material are materials that permit electrons to flow freely from particle to particle, some material used as conductors for all kind of windings required in electrical machines, apparatus and devices. These material are also used as conductor in transmission and distribution of electrical energy.

Conductor material can be categorized into two.

low resistivity

Silver
Copper
Gold
Aluminum
Iron
Steel
Sea water
Concrete (not all)

high conductivity materials.

Platinum
Brass
Bronze
Graphite
Dirty water

Silver has the highest electrical conductivity of all metals. However this material not used to make electric wires because it is expensive. Therefore is commonly operated under DC supply.
Copper are good conductor for AC supply system. However it have weak thermal properties. Maximum operating temperature is 60 deg. Celsius. If temperature kept rising, the material will change form to liquid state.
Gold are rated as the third, this material is not good when AC supply is applied. This material are commonly found in DC electronics circuits and IC due to it capability to operate high frequencies signals and processes. Example of high frequency application like computer chips and mobile phones.
Aluminum have good thermal properties, it is commonly used as heat sinks device in common electronics circuit board. However in AC supply, this material can handle higher voltage properties compare to other materials and the operating temperature can range from 40 ~ 150 deg.Celsius.
Iron are commonly used as contacts in both AC and DC supply. These material are fragile and soft, if current flow on these material may generate heat which can easily break or cause open line. When short happen on the iron, it will explode or causes contact to weld permanently on the contact point.
Steel are hard material which have lower properties in electrical.

Insulator Material

Material which restricts current to flow. Insulator material must have a good protection for electrical conductor.

Insulator material used for electrical installation.

Conductor material refer to material that allows current to flow though it.

Rubber
Glass
Pure water
Oil
Air
Diamond
Dry wood
Dry cotton
Plastic
Asphalt

Other strong insulators

Fiberglass
Dry paper
Porcelain
Ceramics
Quartz

1. Rubber

Rubber is insulated with vulcanised natural rubber (VIR). Good insulation properties which can handle temperature up to 90 deg.Cel. This insulator be use on indoor or outdoor installations. This cable insulation material is also known as weather proof. When (ordinary) electrical potentials are applied at the opposite ends of such rubber, the electrons of the valence band are hardly elevated into the conduction band and hence no flow of electrical charge is possible across the rubber matrix.

2. Polyvinyl Chloride (or PVC)

Characteristics maximum up to 60 deg. Cel and withstand chemical environment. P.V.C. operating temperature must not be allowed to exceed 70°C else it will damage the insulation material. When this cable is exposed to sunlight it may be degraded by ultra-violet radiation and cause cable insulation to crack and brited.

3. Paper

Good insulation properties able to absorb moisture and vapor. This type of insulator is best for power cable especially for underground cables. Example of paper insulated material is paper insulated lead covered (PILC).

4. Mineral Insulation

Magnesium oxide powder which is a non-aging factor and able to handle high current and voltage. This material is known as fire-proof compound because it can handle temperature up to 250 deg.Cel. or greater. Since it is hygroscopic (it absorbs moisture from the air) this insulation is kept sealed within a copper sheath. The benefits of MI cable are;

small diameters
great mechanical strength
waterproof,
resistant to radiation and electromagnetic pulses, corrosion resistant.

5. Cross-link polyethene (thermosetting compound)

Cross-linked polyethylene (XLPE) is a thermosetting compound which has better electrical properties and is used for medium and high voltage applications. Thermal setting compound which can handle high voltage and temperature for conductor. Maximum voltage up to 1000V (or 1kV). For power cable the voltage rated up to 500 kV. This cable is also known as PEX, XPE. It is used predominantly in building services pipework systems, hydronic radiant heating and cooling systems, domestic water piping, and insulation for high tension (high voltage) electrical cables. It is also used for natural gas and offshore oil applications, chemical transportation, and transportation of sewage and slurries.

6. Low smoke fume (LSF)

This cable able to reduce fire smoke compare to other insulator material. This is recommended for high rise building office or apartment for purpose of safely evacuate the building in event of fire.

7. Polythene (or polyethylene )

This is a good electrical insulator,the most common plastic material. This material has reduce its production because it becomes easily electrostatics charged.

8. Oil

This is a good insulation material which purpose to reduce arc or spark formation during switching. Commonly used on high voltage and it store in a container body.

Properties of Insulation material

Extreme of current or temperature.
A corrosive or similarly harsh environment.
Higher voltages than the rest of the circuit.

9. Cross-linked Polyolefin

This cable insulations is referred to as XLPO, is a form of insulation that is created through both heat and high pressure. The most important attribute of XLPO is that it is halogen free. The importance of a halogen free cable is one that it will not emit toxic gases when exposed to fire.

Cable constructions

Basic constructions of cable are;

(a) solid conductor is solid material example like copper or aluminum. This solid conductor commonly applied on power cables. Some large size of conductor are harder to bend and required specific pressure to avoid damage.

(b) multi strands inside a single core cable, the number of strands can be 3, 7, 15, 26, 32, 50 or more strand constructed depending on current requirement of any electrical applications. Today all multi-strand cable used for electrical installation must be greater than 7 strand of copper conductor according to cable manufacturing standards. The more strand means more current and less damage on the conductor when stress on bend part of the conductor.

(c) braided wire this cable have a outer layer of wire mesh act as grounding protection and to reduce electrostatic or magnetic charge on its cable. Example of this cable are video coaxial cable or RF cable. The conductor are commonly copper or silver depending on applications.

For reference only.

Stranded wire is composed of smaller strands of solid copper wire twisted together to form a single, larger conductor.

Cable sizing calculations

Cross sectional area (c.s.a) unit is milimeter square (or mm² )

Formula 1: Cross sectional area (c.s.a)

c.s.a = s x 3.144 (pi) x (diameter x diameter) ÷ 4

where ;

s number of strand

pi 3.144

dia each diameter size of conductor per strand

Formula 2 : Area of conductor

A = pi x R²

where ;

R as ref to =( dia ² ÷ 4)

pi - 3.144

dia each diameter size of conductor per strand

For reference only

AC cable types

Common electrical cable can be used for Alternating Current (A.C) or Direct Current (D.C).

There are different type of cables design available in local market.

twin flex rubber cable (red and black color, single core)
armour cable - for underground laying of cables.
non-armoured cable - for power cable rating more than 40 ampere.
multicore flex PVC cable - for signalling or control cables.

Standard Color of conductor standard in Malaysia

Red ( live ) or phase conductor (in three phase it is identified as Line 1)
Black ( neutral ) or phase conductor
Green ( earth) or protective conductor
Yellow ( live ) or phase conductor (in three phase it is identified as Line 2)
Blue ( live ) or phase conductor (in three phase it is identified as Line 3)

Color of conductor for Direct Current (DC) standard in Malaysia

Red ( +ve ) or positive cable
Black ( -ve ) or negative cable
Green ( earth) or grounding

Standard cable length by manufacturer

Standard length of cable for domestic wiring purpose are : 90 to 100 meter per roll sale in the market today.

Cable pricing are subjected to global copper pricing.

Genuine cable are more expensive but the copper conductor is pure 90~96%, commonly this cable are use for sub main cabling.

Precaution : There are many cheap cable sold, beware of such supplier as some conductor material are not pure copper and may cause fire or short circuit fault to happen.

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