WAZIPOINT Engineering Science & Technology: March 2019

Wednesday, March 27, 2019

Why Capacitor and Capacitance are Used Electrical and Electronic Circuit?

The Purpose of Capacitors Using in Electrical Circuit.

Capacitor:

Capacitor is an electrical or electronic device that used to store an electric charge, consisting of one or more pairs of conductors separated by an insulator is known as capacitor.

How Many Types of Capacitor Possible?
Fig- Different Types of Capacitor
Simply we can define, single or multiple conductors or metallic parts when placed in parallel then it form a capacitor.

Capacitance:

The effect or action of capacitance, or the behavior of capacitance is known as capacitance.


By definition of capacitance we can say, a capacitor is a passive two-terminal electronic component that stores electrical energy in an electric field and the effect of a capacitor is known as capacitance. 


The basic formula to calculate the capacitance of parallel plate capacitor is as below:


Equation of Parallel Plate Capacitance Measurement

What is Different Types of Capacitors & Their Characteristics?


The most common kinds of capacitors as per named using dielectric materials and/or anode or cathode are: 


Ceramic capacitors have a ceramic dielectric; Film and paper capacitors are named for their dielectrics; Aluminum, tantalum and niobium electrolytic capacitors are named after the material used as the anode and the construction of the cathode (electrolyte).

Ceramic capacitor:
Ceramic CapacitorThe Ceramic Capacitor is named as uses a ceramic material as the dielectric for capacitor which is a fixed-value capacitor where the ceramic material acts as the dielectric.. In Electronic Engineering, the Ceramic capacitors are the most widely used capacitors in the electronic circuits. These capacitors are mainly used where Ceramics were one of the first materials to be used in the proudhon of capacitors.

Electrolytic capacitor: 

Electrolytic capacitor
An electrolytic capacitor is a type of capacitor that uses an electrolyte to achieve a larger capacitance than other capacitor types. An electrolyte is a liquid or gel containing a high concentration of ions. 

An electrolytic capacitor in short named e-cap which is a polarized capacitor whose anode or positive plate is made of a metal that forms an insulating oxide layer through anodization. This oxide layer acts as the dielectric of the capacitor.

Metallized film Capacitor

Metallized film Capacitor: 

Metallized plastic film capacitors come in a variety of forms, using different materials. They are useful in many applications, especially as leaded components. Film capacitors are those kind of capacitors which use a thin plastic film as the dielectric. This film is especially made extremely thin using a sophisticated film drawing process.


Axial Leaded Film foil Capacitor: 


Film foil Capacitor



Type WPP axial-leaded, polypropylene flm/foil capacitors incorporate non-inductive extended foil construction with epoxy end seals. Type WPP is rated for continuous-duty operation over the temperature range of –55 ºC to 105 ºC without voltage derating. Low ESR, low dissipation factor and the inherent stability make Type WPP ideal for tight tolerance, pulse and high frequency applications. 

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Tantalum Capacitor:

Tantalum Capacitor


A tantalum electrolytic capacitor is an electrolytic capacitor, a passive component of electronic circuits. It consists of a pellet of tantalum metal as an anode, covered by an insulating oxide layer that forms the dielectric, surrounded by liquid or solid electrolyte as a cathode.

Silver Mica Capacitor:

Silver Mica Capacitor


The silver mica capacitor provides close tolerance values with low levels of value change with temperature. Silver mica capacitors are high precision, stable and reliable capacitors

The silver mica capacitor provides close tolerance values with low levels of value change with temperature and are available in small values, and are mostly used at high frequencies

Supercap:
Super-capacitors or in short SuparCap is made with graphene as the conducting plate are capable of storing a charge similar to lithium-ion batteries.



Amazing Facts About Capacitor and Capacitance

  1. A capacitor is an electrical or electronic circuit component that made of two conducting plates separated by a dielectric or non-conducting insulator material;
  2. Capacitor shapes are fixed, either flat or cylinder;
  3. The Leyden jar was the first capacitor created, invented in 1745 by Pieter van Musschenbroek;
  4. The characteristics of a capacitor is also known as capacitance measured in unit farad;
  5. A capacitor’s conducting surfaces are made of a thin film of conductive metal or aluminum foil;
  6. The positively charged plate is known as the anode and the negatively charged plate is known as the cathode;
  7. To get higher capacitance values dielectric materials should be higher dielectric constant;
  8. The example of dielectric materials used in capacitors are ceramic, air, vacuum, paper impregnated with oil or wax, mylar, polystyrene, mica, glass etc.;
  9. When a capacitor is connected to a power source, positive charges transfer to one of the conducting surfaces, and negative charges are transferred to the other conducting surface;
  10. Normally a capacitor can absorb energy from a circuit and store it temporarily and then return the energy to the circuit;
  11. Capacitor can store the energy for long time that used as data memory circuit in computer technology;
  12. Capacitors discharge very slowly, but many can store a charge for years;
  13. Handling a larger size charged capacitor in the wrong way can result in burns or even death;
  14. A capacitor is discharged slowly when a resistor is connected to each leg of capacitor;
  15. Capacitors are measured in a unit named farad after the scientist Michael Faraday; 
  16. Super-capacitors made with graphene as the conducting plate are capable of storing a charge similar to lithium-ion batteries.
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What is the Largest Capacitor in the World?


The Sunvault Energ company collaboration with Edison Power is developing graphene-based super-capacitor technology for use in solar cell arrays. In November 2015 Sunvault announced that announced the creation of the world's largest 10,000 Farad Graphene Supercapacitor. The companies declared that this development is the most significant breakthrough in the development of Graphene Super-capacitors till to date. 


Capacitor Formula:

The formula of capacitor means the total capacitance of a capacitor measured by it's place area and current relations that defined early.
Now, we will find the resultant capacitance when multiple capacitor connect in series or parallel:

Capacitor in Parallel Parallel Capacitor Connection


Capacitor in Series
Capacitor in Series Connection

What is a Capacitor Used for? How is a Capacitor Used in a Motor Circuit?


A run capacitors primary function is to bring the start winding in phase with the run winding. It also adds 30-40 percent more starting torque. But the starting torque is its secondary purpose. Also, the voltage rating of the capacitor- 370 or 440, is the amount of cemf,(counter electromotive force) produced by the windings, magnets, armature, etc of the motor, that the capacitor can handle. 

If a motor produces a back voltage over 370, you must use a 440 rated capacitor. If not, the capacitor will fail. Phase problems occur when a capacitor is either weak or too large for the motor. If a  motor calls for a 7.5 mfd capacitor and the capacitor is weak, the motor will often still start but the capacitor will not be able to bring the star.

Capacitor Working Principle

The capacitance depends on the geometry of the conductors and nature of the medium. A capacitor is a device for storing electric charges. 
Capacitor Working Principle

Consider an insulated conductor (Plate A) with a positive charge ‘q’ having potential V (Fig-a). The capacitance of A is C = q/V.


When another insulated metal plate B is brought near A, negative charges are induced on the side of B near A. An equal amount of positive charge is induced on the other side of B (Fig-b). 


The negative charge in B decreases the potential of A. The positive charge in B increases the potential of A. But the negative charge on B is nearer to A than the positive charge on B. So the net effect is that, the potential of A decreases. Thus the capacitance of A is 
increased.


If the plate B is earthed, positive charges get neutralized (Fig-c). Then the potential of A decreases further. 

Thus the capacitance of A is considerably increased. The capacitance depends on the geometry of the conductors and nature of the medium. A capacitor is a device for storing electric charges.

Sunday, March 17, 2019

Smart Grid Technology and Application

Smart Grid
Fig-Transformer Connection

What is Smart Grid Technology?

A smart grid is an electricity network which includes a variety of equipped and energy measures including smart meters, smart appliances, renewable energy resources, and energy efficiency resources based on digital technology that is used to supply electricity to consumers via two-way digital communication. The term smart-Grid also known as digital-grid that refers to the new digital technology or to modernize the electrical network grid.

How Smart Grid Uses in Electricity Network System?


The expression Smart-grid usually refers to a category of technology folk’s square measure exploitation to bring utility electricity delivery systems into the twenty first century, exploitation computer-based device and automation. 

These systems square measure created potential by two-way communication technology and PC process that has been used for many years in alternative industries. 


They’re getting down to be used on electricity networks, from the facility plants and wind farms all the thanks to the shoppers of electricity in homes and businesses. 


They provide several advantages to utilities and shoppers -principally seen in huge enhancements in energy potency on the electricity grid and within the energy users’ homes and offices.
For a century, utility firms have had to send employees bent on gather a lot of the info required to produce electricity. 

The employees browse meters, explore for broken instrumentality and live voltage, as an example. 


Most of the devices utilities use to deliver electricity have however to be machine-driven and computerized. Now, several choices and product square measure being created out there to the electricity business to modernize it.

Smart Technology Association to Smart Grid


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The grid amounts to the networks that carry electricity from the plants wherever it's generated to shoppers. The grid includes cables, substation-equipment like- transformers, switches, control system and so on.

Much within the approach that smart- phones are recently suggests that a phone with a PC in it, good grid suggests that computerizing the electrical utility grid. It includes adding two-way electronic communication technology to devices related to the grid. 

Every device on the network are often given sensors to collect knowledge (power meters, voltage sensors, fault detectors, etc.), and two-way electronic communication between the device within the field and also the utility’s network operations center. 


A key feature of the good grid is automation technology that lets the utility change and management every individual device or variant devices from a central location.
The number of applications which will be used on the good grid once the info engineering is deployed is growing as quick as creative firms can produce and turn out them. 

Advantages embrace increased cyber-security, handling sources of electricity like wind and alternative energy and even integration electric vehicles onto the grid. 


The businesses creating good grid technology or providing such services embrace technology giants, established communication companies and even greenhorn technology companies.

Smart Grid System in Bangladesh

As a modern concept smart grid which refers mainstream power transmission network system solution in Bangladesh, transmission system engineers should be acquainted with the knowledge of Smart transmission or smart grid System.

In its national leadership role, Power Grid may have partnered with key stakeholders from business, academia, and state governments to modernize the nation’s electricity delivery system. Power Grid and its partners determine analysis and development (R&D) priorities that address challenges and accelerate transformation to a better grid, supporting demonstration of not solely good grid technologies however additionally new business models, policies, and social group advantages. Power Grid has incontestable leadership in advancing this transformation through cooperative efforts with energy regulatory authority on good Grid.

Aligning Stakeholders to Achieve Smart Grid Network


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In leading a national transformation to a better grid, Power Grid may begin to outline not solely a vision for the long run electrical delivery system however additionally the practical characteristics. 

Power Grid take initiative to form a practicum involving regulators, utilities, vendors, legislators, analysis establishments, universities, and alternative stakeholders to forge a standard vision and scope for the good grid. 


This biennial effort must result in identification of the principal good grid practical characteristics that comprise the muse of Power Grid’s good grid program.

As outlined by the principal characteristics, Power Grid can encompass a vision of a wise grid that uses digital technology to boost reliability, resiliency, flexibility, and potency (both economic and energy) of the electrical distribution system. The strategy to realize this vision hinges upon activities that directly address the technical, business, and institutional challenges to realizing a better grid.

Smart grid demonstrations and preparation activities cash in of the chemical action impact of considerable investments within the producing, getting and installation of devices and systems. 

These activities leverage efforts below approach within the analysis and development activity space and can facilitate develop important performance and proof-of-concept knowledge. 


This activity space is additionally developing a framework for analyzing good grid metrics and advantages, which are important to assist, build the business case for cost-efficient good grid technologies.
Research and development activities advance good grid practicality by developing innovative, next-generation technologies and tools within the areas of transmission, distribution, energy storage, power physics, and cyber security and also the advancement of precise time-synchronized measures of sure parameters of the electrical grid.
Interoperability and Standards activities make sure that new devices can interoperate in very secure surroundings as innovative digital technologies square measure enforced throughout the electricity delivery system, advancing the economic and energy security of us. 

The continuing good grid ability method guarantees to steer to versatile, uniform, and technology-neutral standards that modify innovation, improve client selection, and yield economies of scale. 


Ability and standards activities don't seem to be restricted to technical info standards; they need to be advanced in conjunction with business processes, markets and also the restrictive surroundings.
Interconnection coming up with and analysis activities produce larger certainty with relation to future generation, as well as characteristic transmission necessities below a broad vary of other electricity futures (e.g., intensive application of demand-side technologies) and developing semi permanent interconnection-wide transmission growth plans.
Monitoring national progress activities establish metrics to point out progress with relation to overcoming challenges and achieving good grid characteristics. 

TRANSMISSION AND DISTRIBUTION OF ELECTRICAL POWER EFFICIENT AND SMARTLY

High Voltage Power Transmission Tower

Transmission and Distribution of Electrical Power Efficient and Smartly.

Considering the main parts of a typical Transmission & Distribution network, here are the average values of power losses at the different steps:


1-2% – Step-up transformer from generator to Transmission line

2-4% – Transmission line
1-2% – Step-down transformer from Transmission line to Distribution network
4-6% – Distribution network transformers and cables

The overall losses between the power plant and consumers is then in the range between 8 and 15%.

Except some isolated individual normal generation, most of national grid electricity is not used in the same place where it is generated. Meaning is that some individual normal scale generator may produce electricity for industrial, commercial or residential purposes where it used; but mass scale produced electricity actually generates far distance from consumer or city center.   Sense is that long-distance electrical transmission and distribution systems are necessary; that is ours topic today Transmission and Distribution of Electrical Power Efficient and Smartly.

There are many obligations, advantages and disadvantages of electrical power generation, transmission and distribution from distance to consumer end; but todays focus only energy losses due to transmitting electricity over distance via networks. Electrical energy losses are very well known to us as system loss.

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There is a myth here in Bangladesh, system losses means it is causes of some dishonest employees of the utility company. Fact is that without system losses electrical network is not possible ever. Following efficient and smart electrical energy transmission and distribution system this losses may keep in economic level, not in zero level.

In presence of high electrical power demand compare to less power generation in Bangladesh we need to minimize this loss to achieve the main goals: Reduce resource consumption while delivering more power to users. Reducing consumption can be done in at least two ways: deliver electrical energy more efficient and smartly and change consumer habits.

Transmitting electrical energy from generating station to user’s end through electrical transmission and distribution network require power cable, power transformer, operating and protective equipments which create three types of energy loss:

Energy is lost as heat in copper or aluminium conductor, causes joule effect;

Energy dissipates into a magnetic field which is magnetic loss;

Energy is absorbed in insulating materials, causes of dielectric effect.

Above-mentioned causes for loss of electricity is totally technical, expert and engineers only can control this type of losses. Others way electricity user also can control the loss and reduce their consumption just changing their habits.

Changing consumer habits needs smart awareness-raising programmes, taking undertaken by governments or activist groups over and over again. Simple things, such as turning off lights in unoccupied rooms, or switching off the television/electronic devices at night (not just putting standby mode), use water pump/ laundry at non-peak hour, or setting the air-conditioner temperature at 25oC.


Technology is changing and improving day by day, of course also for electrical energy transmitting system. More efficient and smart conductors, transformers and equipments are building for energy transmission and distribution network. High efficiency transformers, superconducting transformers, high temperature superconductor are new smart and efficient technologies in this side.

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Just getting idea, conductor losses about 2.5% to 3%, transformer and equipment losses about 1% to 2%. Imagine what is our benefit if 1% energy is saved or loss is reduced; say our electricity generation is 10,000 mega watts. 1% loss means 100 mega watts that can electrify more 20,000 houses, in rural area it may be 100,000 houses. So, you electricity user can efficient and smart your electrical power transmission and distribution of system and light up more houses just switching off your un-occupied rooms. 

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OUTDOOR STRUCTURE FOR HIGH VOLTAGE POWER CABLE

Outdoor Steel Structure for 132kV HV Power Cable
Fig-A Typical Outdoor Grid Substation

Outdoor Steel Structure Design and Installation for HV & EHV Power Cable

The structures shall be designed to carry cable sealing ends, cables and cleats, earthing bars, earth disconnecting links, sunshields and other fittings  should be followed an adequate design manner.

Each sealing end should be provide with a separate structure which be positioned so as to align with the phase center distances of the substation equipment but not less than the minimum electrical and safety clearness as international standard like specified in BS 162.

All structures should be equipped with a suitable framework mounted immediately below the sealing ends to accommodate a phase plate in a conspicuous position. All phase plates shall be manufactured from mild steel sheet with vitreous enameled finish.

Don’t compromise to provide for fixing and bonding copper fittings as may be necessary to accommodate all apparatus affixed thereto and to secure the structures to their foundations.

Factors of Safety on Outdoor Structure for 132kV Power Cable

The factor of safety for each complete structure and foundation should not be less than 2.0, based upon the maximum working loadings specified and described below.

In calculations of the factor of safety the strength of compression members should be based on the crippling loads as International Standard formula.

The strength of both tension and compression members should be based on the elastic limit and the rate of unsupported length to their least radius of gyration should not be more than:
120 - for main members
200 - for braces
250 - for redundant members
350 - for members loaded in tension only

Maximum Simultaneous Working Loads on Outdoor Structure

The assumed maximum simultaneous working loads on the structures should be reckoned as follows:

Wind Loading of Structure

i) A wind pressure of 1427 N/m2 applied at right angles to the lines on the whole projected areas of phase conductors of 1686 n/m2 in the case of earth wires. A wind pressure of 1427 N/m2 shall also be applied to the projected area of each insulator set.

ii) A wind pressure of 4280 N/m2 on the whole projected area of any one face of the structure.

Vertical Loading on Structure

Vertical loadings should include dead weight of all conductors insulator and equipment and the self weight of the structure. 

All structures also should be capable of supporting a loading of 150 kg per phase to allow for imposed loads of men and tools during maintenance however this loading is not to be combined with other loadings in checking the overall factor of safety.


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Design of Outdoor Steel Structure for 132 kV Power Cable Installation

132kV Power Cable Outdoor Steel Structure Design
Fig-CAD drawing for steel structure
The compression members shall consist of rolled steel sections and the tension members of rolled steel sections or flats. The design shall be such as to keep the number of different parts as small as 

Pockets or depressions likely to hold water shall be avoided and if not avoidable shall be properly drained.

Steel structures should be fabricated from either mild steel BS4360 grade 43A or high tensile steel BS 4360 part 2 grade 50C. Notable that all material should be free from blisters, scale or other defects.

All members should be stamped or marked for erection purposes.
All members, fittings, bolts, washers, screwed rods, nuts etc., should be galvanized.

All parts shall be secured by means of bolts and nuts and screwed rods whose minimum diameter shall be 12.5 mm. All nuts and pins shall be locked in position by means of lock washers or other approved devices. Taper washers should be provided where necessary.

When in position, all bolts or screwed rods shall project through the corresponding nuts but by no more than 10 mm. Bolt heads rather than nuts shall be on the outer faces of members.

No bolts hole shall be more than 1.5 mm larger than the diameter of the bolt, but after galvanizing sufficient clearance shall be left for insertion of the bolts.

During erection care shall be taken to ensure that the structures are not strained or damaged in any way and that the treated surfaces are not injured. Rust streaks and foreign matter deposited on galvanized surfaces during transport and storage shall be removed.

Workmanship of Steel Structure

All members shall be cut to jig and all holes shall be drilled or punched to jig so that when the members are in position the holes will be truly opposite each other before being bolted up. Drifting or reaming of holes will not be allowed.

The drilling, punching, cutting and bending of all steelwork and the removal of sharp edges and burrs shall take place before galvanizing.

Approved steel gauges of the stud type shall be provided to enable checking of members as may be considered necessary by the qualified Engineer.

Built members shall when finished be true and free from al kinks, twists and open joints and the material shall not be defective or strained in any way.

In order to check the workmanship, not less than 1% of the members corresponding to each type of support shall if required be selected at random and assembled to form complete supports in the presence of the qualified Engineer at the manufacture’s works.

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Sun-shields on Structure for Power Cables

At places where power cables are brought above ground level e.g. sealing end structures, proper sun shields shall be provided and fitted. These shall comprise of perforated cable trays galvanized and fitted externally to each. Sealing end structure such as to shield the cable from sunlight and allow air flow over the cable.

Marking on Steel Structure Sections

All steel sections, fish-plates and gusset plates should be indelibly marked with an assembly code number or letter, or a combination of both, to facilitate quick recognition and correct assembly. If this identification is stamped on to the member, it’s may  applied before galvanizing.

Wednesday, March 13, 2019

What is the Meaning of XLPE for Power Cable?

What Is XLPE or Cross Linked Polyethylene?

In straight, the meaning of XLPE is cross-linked polyethylene. Cross-linked polyethylene is widely used as electrical insulation in power cables. Especially for medium to High and Extra-high Voltage power cable recently using XLPE insulation. Actually XLPE is the most common polymeric insulation material.

Generally Low Voltage- 11 kV and below cable system use PVC and medium to high and extra-high voltage- 33kv and above uses XLPE as their insulation.

Main Feature of XLPE and PVC Insulation Cable


PVC insulated Cable can work at maximum 70 Centigrade temperature, where XLPE insulated Cable can works at 90 Centigrade.

During short circuit condition around three second (3 sec) PVC insulated Cable can last up to at 160 Centigrade where XLPE insulated Cable up to 250 Centigrade.


Usually service life of XLPE insulated cable is longer than PVC insulated cable.


XLPE insulated Cable is more environment friendly than PVC insulated Cable because XLPE is not containing chlorine which will release toxic gases at burning time.



PVC insulated cable is better to prevent penetrated environment like water proof performance than the XLPE insulated cable.


XLPE insulated cable usually little costlier than PVC insulated cable.



Electrical Properties of XLPE



The study functioning on black concentration and temperature in heating-cooling cycles found that


Fine black- the resistivity and PTC (positive temperature coefficient) effect did not significantly change, whereas coarse black-  effect of crosslinking‐was to significantly increase the resistivity and reduce the PTC effect.

The main advantages of XLPE is good electrical re-productivity and to practically eliminate the NTC -negative temperature coefficient effect.

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More properties about XLPE

Density (g/cm3) 0.93
Surface Hardness              SD58
Tensile Strength (MPa)    18
Flexural Modulus (GPa)   0.6
Notched Izod (kJ/m)        1.06+
Linear Expansion  (/°C x 10-5)       20
Elongation at Break (%)  350
Strain at Yield (%)             N/Y
Max. Operating Temp. (°C)            90
Water Absorption (%)      0.01
Oxygen Index (%)              17
Flammability UL94           HB
Volume Resistivity (log ohm.cm)  16
Dielectric Strength (MV/m)           21
Dissipation Factor 1kHz   0.0004
Dielectric Constant  1kHz               2.2
HDT @ 0.45 MPa (°C)       60
HDT @ 1.80 MPa (°C)       60
Material. Drying  hrs @ (°C)       NA
Melting Temp. Range (°C)    150 - 170
Mould Shrinkage (%)        3

Mould Temp. Range (°C) 20 -  80


Equipment Grounding for De-energized Construction and Maintenance


Importance of  Equipment Grounding for De-energized Construction and Maintenance:



Why grounding Is Require?
Electricity never give you the second chance. So, for safety 99.99% is not enough until 100%. Working with electrical equipment, switch off the power line is not enough for safe; it is very much essential to ensure de-energized the line by grounding.

How Does Grounding Work?

Sometime we even an expert also make mistake to grounding which electricity may get chance to takeaway our valuable life and property. So, no more literature; come and join the Hubbell Power Systems provided video clip to keep safe all of our colleagues:  Video Clip 

What Is Pipe Earthing And Plate Earthing?

Pipe Earthing is the best form of earthing. This is very cheaper than others in cost. In this method of earthing, a galvanized and perforated pipe of approved length and diameter is placed up right in a permanently wet soil.

The size of pipe depends upon the current following amount  to be supposed  and the type of soil condition, dry or wet. If the moisture of soil is very low ( or decreases in Summer ), in such case the resistance of earth is increases.

Plate Earthing an earthing plate of copper of generally dimensions 60cm×60cm×3mm or of galvanized iron of dimensions 60cm×60cm×6mm is buried into the ground with its face vertical to a depth of not less than 3 meter from ground level. High surface area allow the system to allow the high amount of current flow through the earth without any difficulty.

A normal masonry brick wall enclosure with a cast iron cover on top or an RCC pipe round the earth plate is provided to facilitate it .

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Specifications for Earth Electrodes

Generally we follow the following Earth Electrode specifications: The earthing electrode should not be placed near the building whose installation system is earthed more than 1.5 m away. The resistance of the earth wire should not be more than 1 ohm. The wire use for electrode and circuit should be made up of the same material. The electrodes should be placed in vertical position so that it can touch the layers of the earth. Better to select the size of the conductor should not be less than 2.6 sqmm or half of the wire used for electrical wiring. Bare copper wire is used for earthing and grounding for it's long lasting and good conductive properties. Green 6 THHN (Thermoplastic high heat neutral coating wire) and gauged copper wire of different sizes like 2,4,6,8 etc. are also used for earthing and grounding.

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