Wire joint soldering and UG cable Fundamental of electricity

 Fundamental of electricity - conductors - insulators - wire size measurement - crimping 

• Introduction : - Electricity is one of the today’s most useful sources of energy. Electricity is of utmost necessity in the modern world of sophisticated equipment and machinery. Electricity in motion is called electric current. Whereas the electricity that does not move is called static electricity. 
• Examples of static electricity 

1. Shock received from door knobs of a carpeted room. 
2. Attraction of tiny paper bits to the comb. 

• Structure of matter; - Electricity is related to some of the most basic building blocks of matter that are atoms (electrons and protons). All matter is made of these electrical building blocks, and, therefore, all matter is said to be ‘electrical’.
• Atom  :- Matter is defined as anything that has mass and occupies space. A matter is made of tiny, invisible particles called molecules. A molecule is the smallest particle of a substance that has the properties of the substance. Each molecule can be divided into simpler parts by chemical means. The simplest parts of a molecule are called atoms. Basically, an atom contains three types of sub-atomic particles that are of relevance to electricity. They are the electrons, protons and neutrons. The protons and neutrons are located in the centre, or nucleus, of the atom, and the electrons travel around the nucleus in orbits

• Atomic structure 
  
  
  

1. The Nucleus The nucleus is the central part of the atom. It contains the protons and neutrons in equlal numbrs shown in fig 
2. Protons The proton has a positive electrical charge.  It is almost 1840 times heavier than the electron and it is the permanent part of the nucleus; protons do not take an active part in the flow or transfer of electrical energy
3. Electron It is a small particle revolving round the nucleus of an atom (as shown in Fig ). It has a negative electric charge. The electron is three times larger in diameter than the proton. In an atom the number of protons is equal to the number of electrons.
4. Neutron A neutron is actually a particle by itself, and is electrically neutral. Since neutrons are electrically neutral, they are not too important to the electrical nature of atoms.
5. 
   
   
   
   
   
   
   
   In an atom, electrons are arranged in shells around the nucleus. A shell is an orbiting layer or energy level of one or more electrons. The major shell layers are identified by numbers or by letters starting with ‘K’ nearest the nucleus 97 and continuing alphabetically outwards. There is a maximum number of electrons that can be contained in each shell. Fig  illustrates the relationship between the energy shell level and the maximum number of electrons it can contain sequence. For example, a copper atom which has 29 electrons would have four shells with a number of electrons in each shell as shown in Fig

• Electron distribution The chemical and electrical behaviour of atoms depends on how completely the various shells and sub-shells are filled. Atoms that are chemically active have one electron more or one less than a completely filled shell. Atoms that have the outer shell exactly filled are chemically inactive. They are called inert elements. All inert elements are gases and do not combine chemically with other elements.
• Metals possess the following characteristics.

1.   They are good electric conductors. 
2.  Electrons in the outer shell and sub-shells can move more easily from one atom to another. 
3.  They carry charge through the material

• . The outer shell of the atom is called the valence shell and its electrons are called valence electrons. Because of their greater distance from the nucleus, and because of the partial blocking of the electric field by electrons in the inner shells, the attracting force exerted by nucleus on the valence electrons is less. Therefore, valence electrons can be set free most easily. Whenever a valence electron is removed from its orbit it becomes a free electron. Electricity is commonly defined as the flow of these free electrons through a conductor. Though electrons flow from negative terminal to positive terminal, the conventional current flow is assumed as from positive to negative.

• Conductors, insulators and semiconductors
• Conductors  A conductor is a material that has many valance electrons permitting electrons to move through it easily. Generally, conductors have many valence shells of one, two or three electrons. Most metals are conductors. Some common good conductors are Copper, Aluminium, Zinc, Lead, Tin, Eureka, Nichrome, are conductors, where as silver and gold are very good conductors 
• Insulators  An insulator is a material that has few, if any, free electrons and resists the flow of electrons. Generally, insulators have full valence shells of five, six or seven electrons. Some common insulators are air, glass, rubber, plastic, paper, porcelain, PVC, fibre, mica etc.

• Semiconductors A semiconductor is a material that has some of the characteristics of both the conductor and insulator. Semiconductors have valence shells containing four electrons. Common examples of pure semiconductor materials are silicon and germanium. Specially treated semiconductors are used to produce modern electronic components such as diodes, transistors and integrated circuit chips.
• Simple electric circuit  A simple electrical circuit is one in which the current flows from the source to a load and reaches back the source to complete the path. As shown in Fig , the electrical circuit should consist of the following. 
  
  
  
  
• An energy source (cell) to provide the voltage needed to force the current through the circuit.
• Conductors through which the current can flow.
•  A load (resistor ‘R’) to control the amount of current and to convert the electrical energy to other forms. 
• A control device (switch ‘S’) to start or stop the flow of current.
• In addition to the above, the circuit may have insulators (PVC or rubber) to confine the current to the desired path, and a protection device (fuse ‘F’) to interrupt the circuit in case of malfunction of the circuit (excess current).

• Electric current
  
  Fig  shows a simple circuit which consists of a battery as the energy source and a lamp as the resistance. In this circuit, when the switch is closed, the lamp glows because of the electric current flows from the +ve terminal of the source (battery) via the lamp and reaches back the –ve terminal of the source.   Flow of electric current is nothing but the flow of free electrons. Actually the electrons flow is from the negative terminal of the battery to the lamp and reaches back to the positive terminal of the battery. However direction of current flow is taken conventionally from the +ve terminal of the battery to the lamp and back to the –ve terminal of the battery. Hence, we can conclude that conventional flow of current is opposite to the direction of the flow of electrons. Throughout the Trade Theory book, the current flow is taken from the +ve terminal of source to the load and then back to the –ve terminal of the source.

• Ampere The unit of current (abbreviated as I) is an ampere (symbol A). If 6.24 x 1018 electrons pass through a conductor per second having one ohm resistance with a potential difference of one volt causes one ampere current has passed through the conductor.
• Ammeter We know the electrons cannot be seen and no human being can count the electrons. As such an instrument called ammeter is used to measure the current in a circuit. As an ammeter measures the flow of current in amperes it should be connected in series with the resistance (Load). as shown in Fig . For the decimal and decimal sub multiples of the ampere we use the following expressions.   
  
  
  
  
• 1 kilo-ampere = 1 kA = 1000 A = 1 x 103 A 
• 1 milli-ampere = 1 mA = 1/1000 A = 1 x 10–3A 
• 1 micro-ampere = 1 μA = 1/1000000 A = 1 x 10–6A
• In order to move the electrons in a circuit- that is to make the current to flow, a source of electrical energy is required. In a torch light, the battery is the source of electrical energy. The terminals of the battery are indicated in the circuit symbol by two lines, the longer line for the positive and the shorter for the negative terminal. Within the battery the negative terminal contains an excess of electrons whereas the positive terminal has a deficit of electrons.
   
  
  The battery is said to have an electromotive force (emf) which is available to drive the free electrons in the closed path of the electrical circuit. The difference in the distribution of electrons between the two terminals of the battery produces this emf.                                                                         In Simple, Electromotive force (EMF) is the electrical force, which is initially available in elecrical source, cause to move the free electrons in a conductor Its unit is ‘Volt’ It is denoted by letter ‘E’ It cannot be measured by any meter. It can be only calculated by using the formula E = Potential Difference (P.D) + V. drop = p.d + V.drop  E = V + IR Electromotive force is essential to drive the electrons in circuit This force is obtained from the source of supply i.e. Torch lights, dynamo System International (SI) unit of electromotive force is Volts (symbol ‘E’)

• You're asking about the differences between EMF (Electromotive Force), Potential Difference (PD), and Terminal Voltage. These terms are often used in the context of electrical circuits and can be a bit confusing because they are all measured in Volts.

  Here's a breakdown of each, followed by a comparative chart. Unfortunately, I cannot provide an image directly in this text-based format. However, the descriptions and chart below should give you a clear understanding.

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  Understanding the Concepts

  1. Electromotive Force (EMF or $ϵ$)

  • Definition: EMF is the maximum potential difference that a source (like a battery, generator, or solar cell) can provide when no current is being drawn from it (i.e., in an open circuit).¹ It represents the energy per unit charge converted from other forms of energy (chemical, mechanical, light) into electrical energy within the source.
  • Nature: It's the "cause" or the driving force that establishes a potential difference. It's essentially the ideal voltage of the source.
  • Measurement: Ideally measured with a potentiometer or a high-resistance voltmeter when no current flows.²
  • Relation to Internal Resistance: EMF is independent of the circuit's external resistance.³ It's the inherent property of the source.

  2. Potential Difference (PD or $V$)

  • Definition: Potential Difference, often simply called "voltage," is the amount of work done or energy dissipated per unit charge as it moves between two points in an electrical circuit.⁴ It represents the "drop" in electrical potential energy as charge moves through a component (like a resistor, bulb, or motor).⁵
  • Nature: It's an "effect" or the actual voltage drop across a component when current is flowing through it.
  • Measurement: Measured with a voltmeter connected in parallel across the two points.⁶
  • Relation to Resistance: The potential difference across a component is directly proportional to the current flowing through it and its resistance (Ohm's Law: $V=IR$).⁷

  3. Terminal Voltage ($V_{terminal}$)

  • Definition: Terminal voltage is a specific type of potential difference.⁸ It's the actual voltage measured across the terminals of a source (like a battery) when current is being drawn from it (i.e., in a closed circuit).
  • Nature: It's the voltage available to the external circuit.
  • Relation to EMF and Internal Resistance: When a current (I) flows through a source with internal resistance (r), some voltage is "lost" due to this internal resistance.⁹ This "lost voltage" is Ir. Therefore, the terminal voltage is always less than the EMF when current is flowing.¹⁰
    • Formula: $V_{terminal}=ϵ-Ir$
    • If no current is flowing ($I=0$), then $V_{terminal}=ϵ$.
  • Measurement: Measured with a voltmeter across the terminals of the source while it is connected to a load.¹¹

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  Comparative Chart: EMF vs. Potential Difference vs. Terminal Voltage

  Feature	Electromotive Force (EMF, ϵ)	Potential Difference (PD, V)	Terminal Voltage (Vterminal​)
  Definition	Maximum potential difference of a source when no current is drawn.	Energy dissipated per unit charge between two points in a circuit.	Actual voltage across the terminals of a source when current is drawn.
  Nature	Cause; ideal voltage of the source.	Effect; voltage drop across a component.	Actual voltage delivered to the external circuit by the source.
  Measured When	Circuit is open (no current flowing).	Current is flowing through the component.	Current is flowing from the source to the external circuit.
  Symbol	ϵ (epsilon) or E	V	Vterminal​ or V (when referring to source output under load)
  Unit	Volt (V)	Volt (V)	Volt (V)
  Magnitude	Constant characteristic of the source.	Varies depending on the component's resistance and current.	Always less than EMF when current flows ($V_{terminal}=ϵ-Ir$). Equal to EMF when no current flows.
  Dependence on Circuit Resistance	Independent of external circuit resistance.	Depends on the resistance of the specific component.	Depends on the external load resistance and internal resistance.
  Energy Conversion	Converts non-electrical energy (chemical, mechanical, light) to electrical energy.	Converts electrical energy to other forms (heat, light, mechanical) in a component.	Represents the electrical energy available to the external circuit.
  Analogies	The "push" of the pump in a water circuit.	The pressure drop across a pipe or valve.	The actual pressure available at the outlet of the pump after considering losses within the pump itself.

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  • EMF is the fundamental potential generated by a source.¹²
  • Potential Difference is the general term for voltage drop across any part of a circuit.
  • Terminal Voltage is the specific potential difference across the source's terminals when it's supplying current, which is EMF minus the voltage drop due to the source's internal resistance.¹³

• Resistance (R) In addition to the current and voltage there is a third quantity which plays a role in a circuit, called the electrical resistance. Resistance is the property of a material by which it opposes the flow of electric current.

• International Ohm It is defined as that resistance offered to an unvarying current (DC) by a column of mercury at the temperature of melting ice (i.e. 0°C), 14.4521 g in mass, of constant crosssectional area (1 sq. mm) and 106.3 cm in length.

• International ampere One international ampere may be defined as that unvarying current (DC) which when passed through a solution of silver nitrate in water, deposits silver at the rate of 1.118 mg per second at the cathode.

• Internation volt It is defined as that potential difference which when applied to a conductor whose resistance is one international ohm produces a current of one international ampere. Its value is equal to 1.00049V

• Conductance The property of a conductor which conducts the flow of current through it is called conductance. In other words, conductance is the reciprocal of resistance. Its symbol is G (G = 1/R) and its unit is mho represented by Ʊ . Good conductors have large conductances and insulators have small conductances. Thus if a wire has a resistance of R , its conductance will be 1/R

• Quantity of electricity As the current is measured in terms of the rate of flow of electricity, another unit is necessary to denote the quantity of electricity (Q) passing through any part of the circuit in a certain time. This unit is called the coulomb (C). It is denoted by the letter Q. Thus Quantity of electricity = current in amperes (I) x time in seconds (t) or Q = I x t 

• Coulomb It is the quantity of electricity transferred by a current of one ampere in one second. Another name for the above unit is the ampere-second. A larger unit of the quantity of electricity is the ampere-hour (A.h) and is obtained when the time unit is in hours                                                                       1 A.h = 3600 Asec or 3600 C

• Types of supply 

  AC (Alternating Current) vs. DC (Direct Current) Supply

  Parameter	AC (Alternating Current)	DC (Direct Current)
  Flow of Current	Changes direction periodically	Flows in one direction only
  Waveform	Sine wave (also triangular or square)	Straight line
  Source Examples	Generators, power plants, mains supply	Batteries, solar cells, DC generators
  Frequency	50 Hz (India), 60 Hz (USA)	Zero (no frequency)
  Voltage Level	Can be stepped up/down easily using transformers	Hard to change without converters
  Transmission	Efficient over long distances	Not suitable for long-distance transmission
  Applications	Home appliances, industrial equipment	Electronics, battery-powered devices
  Power Loss	Less over distance (high voltage, low current transmission)	More over distance due to resistance
  Polarity	Alternates polarity	Fixed polarity (+ and -)
  Conversion	Can be converted to DC using rectifiers	Can be converted to AC using inverters

  AC Power Sources:

  These include generators and power plants that produce alternating current.

  

  

  
  

  DC Power Sources:

  These include batteries and solar cells that produce direct current.

   
  

  
  
  

  

  
  

• It is crucial to understand the concept of polarity in electrical circuits, especially when dealing with both Alternating Current (AC) and Direct Current (DC) supplies. While the nature of polarity differs between the two, its importance remains paramount for safety, proper device function, and preventing damage.

  AC Supply Polarity:

  Nature of AC Polarity:

  • Alternating Direction: In AC, the direction of current flow and the voltage polarity (positive and negative) constantly reverse periodically. This is typically represented as a sine wave. For example, in North America, standard AC switches direction 120 times per second (60 Hz).
  • No Fixed Positive/Negative: Unlike DC, there isn't a fixed positive or negative terminal in the way we think of a battery. The "hot" or "live" wire continuously changes polarity, while the "neutral" wire is typically bonded to ground near the source, maintaining a potential close to zero.

  Importance of AC Polarity (for safety and specific applications):

  • Safety (Hot and Neutral): Even though AC "alternates," there's a convention for "hot" (line) and "neutral" wires in household wiring. The "hot" wire carries the fluctuating voltage, while the "neutral" wire serves as the return path and is typically at or near ground potential.
    • Proper Wiring: Correctly wiring a device ensures that safety features like switches and fuses are placed on the "hot" line, interrupting the power flow effectively when the device is turned off. If hot and neutral are reversed, the device's internal wiring might remain live even when the switch is off, posing a shock hazard.
    • Polarized Plugs: Many two-prong AC plugs are "polarized," meaning one prong is wider than the other. This ensures the plug can only be inserted one way, aligning the appliance's internal wiring with the "hot" and "neutral" lines of the outlet for safety.
    • Grounding: In three-prong plugs, a dedicated ground wire provides an additional safety path, preventing electric shock if a fault occurs and the appliance's metal casing becomes energized.
  • Audio Equipment: In sensitive audio systems, correct AC polarity can influence sound quality by reducing induced noise and ensuring proper grounding.
  • Specific AC Loads: While many simple AC loads (like incandescent light bulbs) are not sensitive to the "hot" and "neutral" orientation for their basic function, some devices with internal electronics or switches are designed with specific polarity in mind for safety and optimal performance.

  DC Supply Polarity:

  Nature of DC Polarity:

  • Fixed Direction: In DC, current flows in a single, constant direction, from the positive terminal to the negative terminal (conventionally).
  • Fixed Positive and Negative: DC sources (like batteries, power adapters, solar panels) always have a distinct positive (+) and negative (-) terminal.

  Importance of DC Polarity:

  • Device Functionality: Most electronic components and devices that operate on DC are designed to receive power with a specific polarity.
    • Semiconductors (Diodes, Transistors, ICs): Components like diodes, LEDs (Light Emitting Diodes), transistors, and integrated circuits (ICs) are highly sensitive to polarity. Reversing the polarity can prevent them from functioning correctly or, more commonly, cause immediate and irreversible damage (e.g., burning out).
    • Motors: DC motors typically rotate in a specific direction based on the applied polarity. Reversing the polarity will usually reverse the direction of rotation.
    • Batteries: Batteries store chemical energy and are designed for current to flow into them during charging (positive to positive, negative to negative) and out of them during discharge. Connecting a battery with reverse polarity can damage the battery itself, lead to overheating, or even cause a fire or explosion.
  • Charging Circuits: Battery chargers and devices with rechargeable batteries strictly require correct DC polarity for safe and effective charging. Incorrect polarity can damage both the charger and the battery.
  • Electrolytic Capacitors: These types of capacitors are polarized and must be connected with the correct polarity. Connecting them backward can cause them to overheat, bulge, leak, or even explode.
  • System Integrity and Protection: Many DC power systems incorporate reverse polarity protection circuits (e.g., using diodes or MOSFETs) to prevent damage if a user accidentally connects the supply backward. However, these protection circuits might not always be present or robust enough for severe misconnections.
  • Solar Panels: Solar panels generate DC power, and their output has a defined positive and negative. Proper polarity is essential for connecting them to charge controllers, inverters, and batteries in a solar power system. Reversing polarity in a solar string can lead to short circuits and damage to modules or inverters.

  Consequences of Incorrect Polarity (especially for DC):

  • Component Damage: The most common consequence is the destruction of sensitive electronic components (IC's, transistors, diodes, etc.) due to excessive current or voltage in the wrong direction.
  • Overheating and Fire Hazard: Incorrect polarity can lead to short circuits, excessive current draw, and overheating, which can result in smoke, fire, or explosions.
  • Malfunction or Non-Operation: The device simply might not work, or it might exhibit erratic behavior.
  • Battery Damage: Batteries can be permanently damaged, lose capacity, or become a fire hazard if connected with reverse polarity.
  • Safety Risks: Direct contact with incorrectly wired AC systems can lead to severe electric shocks.

  
  

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  Effects of Electric Current

  • Chemical Effect: Current decomposes conducting liquids (electrolytes). Used in electroplating, battery charging, metal refining.
  • Heating Effect: Resistance of conductors converts electrical energy into heat. Applied in heaters, lamps, electric presses.
  • Magnetic Effect: Current creates a magnetic field, deflecting compasses or forming electromagnets. Essential for motors, fans, electric bells.
  • Gas Ionization Effect: Electrons ionize gases, causing them to emit light. Seen in fluorescent tubes, neon lamps.
  • Special Rays Effect: Electric current can generate specialized radiation like X-rays and laser rays.
  • Shock Effect: Current passing through living bodies can cause shock or death. (Note: The text's mention of "give light" for controlled current is likely a misstatement; it refers to other controlled medical applications).
    
    
    Conductors - insulators - wires - types

• Conductors:

  • Definition: Materials with high electron mobility (many free electrons) that can carry an electric current.
  • Examples: Silver, copper, aluminum, and most other metals.
  • Regulations: Their use and insulation are governed by IE regulations and BIS (ISI) code of practice in India, ensuring safety from electrical hazards.
  • Common Forms: Wires and cables are the most prevalent types, manufactured in various forms for different applications.
  • Function: They create an unbroken path for electricity from generation to consumption.
  • Materials: Typically made of copper or aluminum.
  • Heat Generation: Current flowing through a conductor generates heat, proportional to the square of the current and the conductor's resistance ($H\propto I^{2}R$).
  • Cross-sectional Area:
    • Needs to be large enough for low resistance to minimize heat generation.
    • Needs to be small enough to keep cost and weight down.
    • Optimal size balances current carrying capacity with acceptable voltage drop and heat generation.
  • Insulation Temperature Limit: Each type of insulation has a maximum safe operating temperature it can withstand.
  • BIS (ISI) Code: Specifies safe maximum current for different conductor sizes, insulation types, and installation environments.
  • Size Specification:
    • Typically specified by diameter in mm or cross-sectional area (e.g., 1.5 sq.mm, 2.5 sq.mm).
    • In India, the old method of using Standard Wire Gauge (SWG) numbers for diameter is still common.
  • Classification: Can be classified by their covering.
  • Bare Conductors:
    • Have no covering.
    • Commonly used in overhead electrical transmission and distribution lines, and for earthing.

  Insulators:

  • Definition: Materials with low electron mobility (few or no free electrons) that cannot easily allow electric current to pass through them.
  • Examples: Wood, rubber, PVC, porcelain, mica, dry paper, and fiberglass.

  Key Concepts Highlighted:

  • Electron Mobility: The fundamental difference between conductors and insulators.
  • Safety Regulations: The importance of standards (IE regulations, BIS/ISI code) for electrical safety.
  • Heat Generation in Conductors: A critical consideration for conductor sizing and material selection.
  • Balancing Design Factors: The trade-offs involved in determining the optimal cross-sectional area of a conductor (resistance, cost, weight, current capacity, voltage drop, heat).
  • Insulation's Role: Crucial for safety and performance, with temperature limits being a key factor.
  • Conductor Sizing: The practical application of electrical principles to ensure safe and efficient operation.

• Insulated Conductors:

  • Feature an insulating coating that electrically isolates the conductor from others and the environment.¹
  • Enables safe grouping of conductors.
  • Additional coverings can provide mechanical strength and protection from elements, moisture, and abrasion.

  Solid and Stranded Conductors:

  • Solid: Contains a single conductor in its core.
  • Stranded: Composed of multiple smaller conductors twisted together to form the core.
  • Number of conductors: 3 to 162.
  • Conductor diameter: 0.193 mm to 3.75 mm (depends on current capacity, cable/overhead line use).
  • Designation (Stranded):
    • Expressed in sq. mm (e.g., 10 sq. mm) for cross-sectional area.
    • Also by number of conductors/diameter in mm (e.g., 7/1.40, where 7 is number of conductors and 1.40 mm is diameter).
    • Alternatively, diameter can be in Standard Wire Gauge (SWG) number (e.g., 7/17).
  • Advantages of Stranded: More flexible and possess better mechanical strength.
  • Current stipulation: Cable size should be in sq. mm or number of conductors/diameter in mm.

  Cable:

  • A length of one or more insulated conductors (single or stranded), laid together.
  • May or may not have an overall mechanical protective covering.

  Cable (Armoured):

  • Features a metal wrapping (tape or wire) for mechanical protection.

  Cable (Flexible):

  • Contains one or more cores, each made of a group of wires.
  • Small core and wire diameters provide flexibility.

  Core:

  • Central part of a cable, typically one or multiple stranded conductors for high conductivity.
  • Common core counts: 1, 2, 3, 3.5, and 4.
  • Each core is individually insulated, with overall insulation around the cores.

  Wire:

  • A solid conductor or an insulated conductor (solid or stranded) subjected to tensile stress, with or without a screen.

  Copper and Aluminium (Conductors):

  • Primary materials used in electrical work.
  • Silver is a better conductor but too expensive for general use.
  • Electrical copper is highly pure (e.g., 99.9%).

  Characteristics of Copper:

  1.Best conductivity after silver.
  2.Highest current density per unit area, requiring less volume for a given current/length.
  3.Can be drawn into thin wires and sheets.
  4.High resistance to atmospheric corrosion, ensuring long service life.
  5.Can be joined without special provisions for electrolytic action.
  6.Durable and has high scrap value.

  Characteristics of Aluminium:

  • Good conductivity, second to copper (60.6% of copper's conductivity). Requires larger cross-section for same current capacity as copper.
  • Lighter weight.
  • Can be drawn into thin wires and sheets, but loses tensile strength with reduced cross-sectional area.
  • Requires precautions when joining.
  • Low melting point 
  • cheaper than copper .

  Property	Copper (Cu)	Aluminium (Al)
  Colour	Reddish	White brown
  Electrical Conductivity (MHO/m)	56	35
  Resistivity at 20°C (Ω·m, 1 mm² cross-section)	0.01786	0.0287
  Melting Point	1083°C	660°C
  Density (kg/cm³)	8.93	2.7
  Temp. Coefficient of Resistance (per °C)	0.00393	0.00403
  Linear Expansion at 20°C (per °C)	17 × 10⁻⁶	23 × 10⁻⁶
  Tensile Strength (N/mm²)	220	70

  
  

• Fundamental Properties of Insulating Materials

  1. Insulation Resistance

     • Resistance to the flow of electrical current through the insulating material.

     • Measured in megohms (MΩ) using a megohmmeter (Megger).

     • Indicates the condition or health of insulation.

  2. Dielectric Strength

     • Maximum potential difference the insulation can withstand without breakdown.

     • Expressed as breakdown voltage.

     • A critical factor in preventing electrical failure.

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  Desirable Characteristics of Insulating Materials

  • High dielectric strength

  • Temperature resistance

  • Flexibility

  • Mechanical strength

  No single material meets all needs, so various insulating materials are used based on application.

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  Types of Insulating Tapes

  1. Rubber Tape

     • Used for insulating joints.

     • Applied under tension to bond layers.

     • Restores insulation but not mechanically strong.

  2. Friction Tape

     • Cotton cloth with adhesive, applied over rubber tape.

     • Lacks insulating properties of rubber tape.

     • Used for mechanical protection, not primary insulation.

  3. Plastic Tape (PVC Tape)

     • Most commonly used insulating tape.

     • Benefits:

       • High dielectric strength

       • Thin and flexible

       • Conforms to shapes and contours

  4. Varnished Cambric Tape

     • Cloth tape with varnish; no adhesive.

     • Comes in sheets or rolls.

     • Ideal for motor lead insulation.

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  Measurement of Wire Sizes – Standard Wire Gauge & Outside Micrometer

  Necessity of Measuring Wire Sizes

  Accurate measurement of wire sizes is crucial for ensuring safety and efficiency in electrical installations. Before executing any wiring job, proper planning is essential. This includes understanding the requirements of the house owner, followed by the preparation of a detailed wiring layout and cost estimate.

  A reliable estimate should include:

  • Determination of current required for various electrical loads.

  • Correct selection of cable type based on the application.

  • Accurate measurement of wire size to ensure it can safely carry the intended current.

  • Estimation of wire quantity required for the project.

  Errors in any of these areas can lead to:

  • Defective wiring, which may not function as intended.

  • Fire hazards, due to overheating wires.

  • Customer dissatisfaction, resulting in conflict and potential rework.

  • Increased costs for both materials and labor.

  Standard Wire Gauge (SWG) Chart:

SWG No.	mm	inch	SWG No.	mm	inch
7/0	12.7	0.500	23	0.61	0.024
6/0	11.38	0.464	24	0.56	0.022
5/0	10.92	0.430	25	0.50	0.020
4/0	10.16	0.402	26	0.46	0.018
3/0	9.45	0.372	27	0.41	0.0164
2/0	8.83	0.348	28	0.38	0.0148
0	8.23	0.324	29	0.36	0.0136
1	7.62	0.300	30	0.31	0.0124
2	7.01	0.276	31	0.30	0.0120
3	6.4	0.252	32	0.27	0.0108
4	5.89	0.232	33	0.25	0.0100
5	5.38	0.212	34	0.23	0.0092
6	4.88	0.192	35	0.20	0.0080
7	4.47	0.176	36	0.19	0.0076
8	4.06	0.160	37	0.18	0.0072
9	3.66	0.144	38	0.15	0.0060
10	3.25	0.128	39	0.14	0.0056
11	2.95	0.116	40	0.12	0.0048
12	2.64	0.104	41	0.10	0.0040
13	2.34	0.092	42	0.09	0.0036
14	2.03	0.080	43	0.08	0.0032
15	1.83	0.072	44	0.07	0.0028
16	1.63	0.064	45	0.06	0.0024
17	1.42	0.056	46	0.05	0.0020
18	1.22	0.048	47	0.04	0.0016
19	1.02	0.040	48	0.03	0.0012
20	0.91	0.036	49	0.02	0.0008
21	0.81	0.032	50	0.01	0.0004
22	0.71	0.028

• Standard Wire Gauge (SWG) The size of the conductor is given by the standard wire gauge number. According to the standards each number has an assigned diameter in inch or mm. This is given in Table .
  
  
  The standard wire gauge, shown in Figure 1 could measure the wire size in SWG numbers from 0 to 36. It should be noted that the higher the number of wire gauge the smaller is the diameter of the wire.  For example, SWG No. 0 (zero) is equal to 0.324 inch or 8.23 mm in diameter whereas SWG No.36 is equal to 0.0076 inch or 0.19 mm in diameter. While measuring the wire, the wire should be cleaned and then inserted into the slot of the wire gauge to determine the SWG number (Fig ). The slot in which the wire just slides in is the correct slot and the SWG number could be read in the gauge directly. In most of the wire gauges to save the trouble of referring to the table, the wire diameter is inscribed on the reverse of the gauge.
• Measurement of wire size by Outside micrometers A micrometer is a precision instrument used to measure a job, generally within an accuracy of 0.01 mm. Micrometers used to take the outside measurements are known as outside micrometers. 
  
  The parts of a micrometer Frame The frame is made of drop-forged steel or malleable cast iron. All other parts of the micrometer are attached to this. Barrel/sleeve The barrel or sleeve is fixed to the frame. The datum line and graduations are marked on this. Thimble The thimble is attached to the spindle and on the bevelled surface of the thimble, the graduation is marked.Spindle One end of the spindle is the measuring face. The other end is threaded and passes through a nut. The threaded mechanism allows for the forward and backward movement of the spindle. Anvil The anvil is one of the measuring faces which is fitted on the micrometer frame. It is made of alloy steel and finished to a perfectly flat surface. Spindle lock-nut The spindle lock-nut is used to lock the spindle at a desired position. Ratchet stop The ratchet stop ensures a uniform pressure between the measuring surfaces.
• Skinning of cables : The installation technique for aluminium cables is the same as that for copper cables. Certain additional precautions are necessary as aluminium has low mechanical strength, less current carrying capacity for the same area of cross-section, low melting point, and is quicker in forming oxides on the surface than copper. Accordingly, while, using aluminium cables proper care is to be taken regarding the following. 

 Handling

 Skinning of the cables 

Connecting the cable ends 

• Handling: Remember that aluminium conductors when compared to copper conductors have less tensile strength and less resistance to fatigue. As such, bending or twisting of aluminium conductors while laying the cables should be avoided as far as possible.
• Skinning of cables: While skinning the insulation from the cables, knicks and scratches should be avoided. As shown in Fig 1, the insulation should not be ringed as there is a danger of nicking the aluminium conductor while ringing the insulation with a knife. Using the knife as shown in Fig 2 at an angle of 20° to the axis of the core will avoid knicking of the conductor.
• Connecting the cable ends The following problems are encountered while connecting aluminium cables to the accessories. The termination holes in the accessories may be undersized. This normally happens in old accessories as they are designed for copper cable ends. Hence, while selecting accessories, a thorough check is necessary of all accessories to ensure whether the holes in the terminating connectors as shown in Fig 4 are suitable to accommodate the specified aluminium conductors. In any case, the strands should not be cut or the conductor filed as shown in  enable insertion in the undersized hole as this operation results in the heating of the cable end on load condition. Joints in electrical conductors are necessary to extend the cables, overhead lines, and also to tap the electricity to other branch loads wherever required

• Cable Selection & Current Carrying Capacity

  The current-carrying capacity of a cable depends on several critical factors:

  1. Key Factors Affecting Cable Rating:

  • Type of conductor: Copper or aluminium.

  • Type of insulation: PVC or other materials.

  • Installation condition: In conduit, buried, or on open surface.

  • Phase configuration: Single-phase or three-phase circuits.

  • Type of overcurrent protection:

    • Coarse (less sensitive, slower response)

    • Close (more sensitive, faster response)

  • Ambient temperature: Higher temperatures reduce current-carrying capacity.

  • Number of cables grouped together: Affects heat dissipation.

  • Length of circuit: Important for voltage drop (covered later).

  ---

  Impact of Overcurrent Protection Type

  PVC-Insulated Cables:

  PVC can degrade if overheated even briefly, so overcurrent protection must limit temperature rise.

  Types of Protection:

  1. Coarse Excess Current Protection

  • Allows operation at 1.5× rated load for up to 4 hours.

  • Devices:

    • Rewirable fuses with fusing factor >1.5

    • Old-style fuse carriers and bases

  2. Close Excess Current Protection

  • Trips within 4 hours at 1.5× load.

  • Devices:

    • HRC fuses

    • Miniature Circuit Breakers (MCBs)

    • Moulded Case Circuit Breakers (MCCBs)

  Government preference: Inspectors recommend close protection (e.g. MCBs) to reduce fire risks.

  ---

  Rating Factors for Cable Capacity

  Protection Type	Rating Factor
  Coarse Excess Current	0.81
  Close Excess Current	1.23

  Formula:

  $$\text{Permissible Current} = \text{Normal Current Capacity} \times \text{Rating Factor}$$

  ---

  Example Calculation:

  • Cable: 1.5 sq.mm Copper

  • Normal rating: 16 A

  With Coarse Protection:

  $$16 \times 0.81 = 13 \text{ A}$$

  With Close Protection:

  $$16 \times 1.23 = 19.7 \approx 20 \text{ A}$$

  ---

  Conversion Between Rating Types:

  To convert a current value between coarse and close protection ratings:

  $$\text{Close protection rating}=\frac{\text{Coarse protection rating}}{0.81}\times 1.23$$

Wire joints - Types - Soldering methods

Joints in electrical conductors are necessary to extend the cables, overhead lines, and also to tap the electricity to other branch loads wherever required. 

• Definition of joint: A joint in an electrical conductor means connecting/tying or interlaying together of two or more conductors such that the union/junction becomes secured both electrically and mechanically.
• Types of joints: In electrical work, different types of joints are used, based on the requirement. The service to be performed by a joint determines the type to be used. Some joints may require to have good electrical conductivity. They need not necessarily be mechanically strong.
• Example : The joints made in junction boxes and conduit accessories. On the other hand, the joints made in overhead conductors, need to be not only electrically conductive but also mechanically strong to withstand the tensile stress due to the weight of the suspended conductor and wind pressure. Some of the commonly used joints are listed below.

1. Pig-tail or rat-tail 2. twisted joints 3. Married joint 4.Tee joint 5.Britannia straight joint 6.Britannia tee joint 7.Western union joint 8.Scarfed joint 9.Tap joint in single stranded conductor

• Pig-tail/Rat-tail/Twisted joint: (Fig ) This joint is suitable for pieces where there is no mechanical stress on the conductors, as found in the junction box or conduit accessories box. However, the joint should maintain good electrical conductivity 
  
  
  
• Married joint: (Fig ) A married joint is used in places where appreciable electrical conductivity is required, along with compactness As the mechanical strength is less, this joint could be used at places where the tensile stress is not too great.

  

  
  

  
  
• Tee joint : This joint could be used in overhead distribution lines where the electrical energy is to be tapped for service connections.