Trade-based questions for ITI trades such as electrician, fitter, mechanic, electronics mechanic, turner, machinist, wireman, welder, refrigeration and AC and other notified trades

Electrician Trade

The Electrician trade syllabus covers a wide range of topics essential for understanding and working with electrical systems. This includes fundamental principles of electricity, safety practices, circuit theory, AC and DC motors and generators, wiring, installation, testing, and troubleshooting. A strong grasp of these concepts is crucial for passing the CBT-2 Part B exam for this trade.

Basic Electrical Principles

Understanding Ohm's Law, Kirchhoff's Laws, and the concepts of voltage, current, and resistance is fundamental. Ohm's Law ($V = IR$) states that the voltage across a conductor is directly proportional to the current flowing through it and its resistance. Kirchhoff's Current Law (KCL) states that the algebraic sum of currents entering a node is zero, while Kirchhoff's Voltage Law (KVL) states that the algebraic sum of voltages around any closed loop is zero. These laws are the bedrock of circuit analysis.

Key concepts include power ($P = VI = I^2R = V^2/R$), energy, and electrical safety. Always remember that electricity can be dangerous, and proper safety precautions, such as using insulated tools, wearing personal protective equipment (PPE), and de-energizing circuits before working on them, are paramount.

AC and DC Circuits

Direct Current (DC) circuits involve current flowing in one direction, typically from batteries or DC power supplies. Alternating Current (AC) circuits involve current that periodically reverses direction, commonly supplied by power grids. Understanding AC concepts like frequency, voltage, and current amplitude, as well as impedance, reactance, and phase, is vital for analyzing AC circuits.

Series and parallel circuits behave differently. In a series circuit, components are connected end-to-end, and the current is the same through all components, while the total resistance is the sum of individual resistances. In a parallel circuit, components are connected across each other, providing multiple paths for current; the reciprocal of the total resistance is the sum of the reciprocals of individual resistances.

Electrical Machines

DC motors convert electrical energy into mechanical energy, and their speed can be controlled by varying the applied voltage or field current. DC generators do the opposite, converting mechanical energy into electrical energy. AC motors, such as induction motors and synchronous motors, are widely used. Understanding their working principles, types, starting methods, and speed control is essential.

Transformers are used to step up or step down AC voltages. The turns ratio determines the voltage and current transformation: $V_p/V_s = N_p/N_s = I_s/I_p$. They operate on the principle of mutual induction.

Wiring and Installation

This section covers the practical aspects of electrical installations, including types of wiring (e.g., concealed, surface), wiring accessories (switches, sockets, junction boxes), types of cables, and wiring diagrams. Knowledge of Indian Electricity Rules and National Electrical Code (NEC) standards is important for safe and compliant installations. Proper earthing or grounding is critical for safety, providing a low-resistance path for fault currents to flow to the ground, preventing electric shock.

Testing and Troubleshooting

Testing involves using instruments like multimeters, megger (insulation tester), tong testers, and oscilloscopes to check voltage, current, resistance, insulation resistance, and waveform. Troubleshooting is the process of identifying and rectifying faults in electrical circuits or equipment. This requires a systematic approach, starting from understanding the symptoms, checking common fault points, and using diagnostic tools.

Fitter Trade

The Fitter trade is a foundational mechanical trade. It involves working with machines, tools, and equipment to assemble, install, maintain, and repair various mechanical systems. Key areas include fitting, machining, sheet metal work, welding, plumbing, and the use of measuring instruments. Precision and attention to detail are critical in this trade.

Fitting and Assembly

Fitting involves shaping, filing, marking, drilling, and assembling metal parts to precise dimensions. This requires skill in using hand tools like files, hacksaws, chisels, hammers, and measuring tools such as rulers, calipers, and micrometers. Assembly involves putting together components to form a complete machine or system, ensuring proper alignment and fit.

Machining Operations

Machining involves using machine tools to shape metal parts. Common machines include the lathe, drilling machine, milling machine, and shaping machine.

• Lathe Machine: Used for turning, facing, threading, and drilling operations on cylindrical or conical surfaces.
• Drilling Machine: Used to create holes in metal parts.
• Milling Machine: Used to cut flat or irregular surfaces using rotating cutters.
• Shaping Machine: Used for producing flat surfaces with a reciprocating cutting tool.

Understanding machine operations, cutting tools, speeds, and feeds is essential for achieving desired shapes and finishes.

Measuring Instruments

Accurate measurement is fundamental to fitting work. Common measuring instruments include:

• Steel Rule: For basic linear measurements.
• Vernier Caliper: For precise measurements of internal and external dimensions, and depth, with accuracy up to 0.02 mm.
• Micrometer: For highly precise measurements of external dimensions, typically with accuracy up to 0.01 mm.
• Dial Indicator: Used to measure small variations or deviations from a surface, useful for checking flatness and alignment.
• Surface Plate: A precision flat surface used as a reference for layout and inspection.

Knowledge of least count and proper usage of these instruments is vital.

Sheet Metal Work

This involves cutting, shaping, and joining thin sheets of metal. Operations include marking, shearing, bending, folding, and riveting. Tools like sheet metal shears, snips, hammers, and stakes are commonly used.

Welding and Joining

Fitters often need to join metal parts. This includes various welding processes like arc welding (SMAW), gas welding (oxy-acetylene), and brazing. Riveting and bolting are also common joining methods. Understanding the principles of different joining techniques and safety precautions is important.

Safety Practices

Working with heavy machinery, sharp tools, and hot processes requires strict adherence to safety regulations. This includes wearing appropriate PPE (safety glasses, gloves, safety shoes), understanding machine guards, lockout/tagout procedures, and fire safety.

Mechanic (Motor Vehicle) Trade

The Mechanic (Motor Vehicle) trade focuses on the diagnosis, repair, and maintenance of automobiles. This involves understanding the various systems of a vehicle, including the engine, transmission, braking system, suspension, steering, electrical system, and fuel system.

Engine Systems

Internal Combustion Engines (ICE) are the heart of most vehicles. Understanding the working principles of four-stroke and two-stroke engines, gasoline (petrol) and diesel engines, is fundamental. Key components include the cylinder block, pistons, connecting rods, crankshaft, cylinder head, valves, camshaft, and timing system. Maintenance involves tasks like oil changes, filter replacements, and tune-ups.

Fuel Systems

This covers the delivery of fuel to the engine. For gasoline engines, it includes carburetors and fuel injection systems (port injection, direct injection). For diesel engines, it involves fuel pumps, injectors, and glow plugs. Understanding emission control systems like catalytic converters is also important.

Electrical Systems

Vehicle electrical systems include the battery, starting system (starter motor), charging system (alternator), ignition system (spark plugs, coils, ECU), lighting, and accessories. Diagnosing electrical faults often requires using multimeters and specialized diagnostic tools.

Transmission and Drivetrain

This includes the clutch, gearbox (manual and automatic), propeller shaft, differential, and axles. The transmission allows the driver to control the vehicle's speed and torque. Understanding how these components work together to transfer power from the engine to the wheels is crucial.

Braking and Suspension Systems

Braking systems (disc brakes, drum brakes, ABS) are critical for safety. Suspension systems (springs, shock absorbers) provide a smooth ride and maintain tire contact with the road. Knowledge of hydraulic systems and components is important for both.

Steering System

This system allows the driver to control the direction of the vehicle. It includes the steering wheel, steering column, steering gear (rack and pinion, steering box), and tie rods. Power steering systems assist the driver.

Diagnostic Tools and Techniques

Modern vehicles rely heavily on electronic control units (ECUs) and onboard diagnostics (OBD-II). Mechanics use scan tools to read fault codes, monitor sensor data, and perform system tests. Understanding diagnostic procedures is key to efficient repair.

Electronics Mechanic Trade

The Electronics Mechanic trade deals with the installation, maintenance, and repair of electronic equipment and systems. This includes understanding basic electronics, digital electronics, communication systems, microprocessors, and troubleshooting electronic circuits.

Basic Electronic Components

A strong foundation in passive components like resistors, capacitors, and inductors is necessary. Understanding active components such as diodes, transistors (BJT, MOSFET), and operational amplifiers (Op-Amps) is also critical. Knowledge of their symbols, characteristics, and applications is essential.

Ohm's Law ($V=IR$) and Kirchhoff's Laws apply here too. Understanding series and parallel combinations of these components is fundamental for circuit analysis.

Semiconductor Devices

Diodes allow current flow in one direction and are used for rectification. Transistors act as switches or amplifiers. Understanding their different types (NPN, PNP for BJTs; enhancement, depletion for MOSFETs) and how they function in circuits is key.

Digital Electronics

This area covers logic gates (AND, OR, NOT, NAND, NOR, XOR), Boolean algebra, combinational circuits (adders, decoders), and sequential circuits (flip-flops, counters, registers). Understanding binary, octal, decimal, and hexadecimal number systems is also important.

Microprocessors and Microcontrollers

These are the "brains" of many electronic devices. Understanding their architecture, instruction sets, memory interfacing, and input/output operations is vital. Microcontrollers are often used in embedded systems.

Communication Systems

This includes principles of analog and digital modulation/demodulation (AM, FM, ASK, FSK, PSK), transmission lines, antennas, and basic concepts of radio and television broadcasting, as well as modern wireless communication (e.g., Wi-Fi, Bluetooth).

Troubleshooting Electronic Circuits

This is a core skill. It involves using tools like oscilloscopes, multimeters, signal generators, and logic analyzers to diagnose faults. A systematic approach, starting from identifying the symptoms, checking power supplies, then signals, and component by component, is crucial. Understanding circuit diagrams is paramount.

Turner Trade

The Turner trade specializes in operating a lathe machine to produce cylindrical, conical, and other shaped parts with high precision. It involves setting up the workpiece, selecting and setting cutting tools, and performing various turning operations.

Lathe Machine Operations

The lathe is the primary machine. Key operations include:

• Plain Turning: Reducing the diameter of a workpiece.
• Step Turning: Creating steps of different diameters.
• Taper Turning: Producing conical surfaces.
• Facing: Machining the end surface of a workpiece to a specified length or flat finish.
• Threading: Cutting external or internal screw threads.
• Knurling: Producing a diamond or straight pattern on the surface for grip.
• Parting Off: Cutting a finished piece from the stock.

Understanding the different parts of the lathe (headstock, tailstock, bed, carriage, leadscrew) and their functions is essential.

Cutting Tools and Materials

Turner's tools are specialized for different operations. They are typically made of High-Speed Steel (HSS), Carbide, or Ceramic materials for durability and heat resistance. Understanding tool geometry (rake angles, clearance angles) is important for efficient cutting and good surface finish.

Speeds and Feeds

Cutting speed ($V_c$) is the peripheral speed of the workpiece relative to the cutting tool. Spindle speed ($N$) is determined by the cutting speed and workpiece diameter ($D$): $N = (1000 \times V_c) / (\pi \times D)$. Feed ($f$) is the distance the tool advances per revolution of the workpiece. Selecting appropriate speeds and feeds depends on the material being cut, the tool material, and the type of operation.

Measurement and Inspection

As with fitting, precise measurement is critical. Turners use calipers, micrometers, height gauges, depth gauges, and dial indicators to ensure their work meets specifications. Thread gauges are used for checking screw threads.

Work Holding Devices

Workpieces are held on the lathe using various devices like the three-jaw chuck, four-jaw chuck, collets, and faceplates, depending on the shape and size of the workpiece and the operation being performed.

Safety Practices

Operating a lathe involves risks from rotating machinery, sharp tools, and flying chips. Safety measures include wearing safety glasses, avoiding loose clothing, ensuring proper guarding, and never stopping the chuck by hand.

Machinist Trade

The Machinist trade is closely related to Turner and Fitter, but it often involves a broader range of precision machining operations on various machine tools, including lathes, milling machines, shapers, and grinders. Machinists work from blueprints to create parts with very tight tolerances.

Advanced Machining Operations

Machinists are proficient in all operations covered under the Turner trade. Additionally, they specialize in milling operations (creating complex shapes, slots, gears), grinding operations (achieving very fine finishes and high accuracy), and the setup and operation of CNC (Computer Numerical Control) machines.

Blueprint Reading

Understanding technical drawings and blueprints is a fundamental skill for machinists. This includes interpreting dimensions, tolerances, surface finish symbols, material specifications, and geometric dimensioning and tolerancing (GD&T).

Tooling and Fixtures

Machinists select and use a wide variety of cutting tools, measuring instruments, and work-holding devices (fixtures and jigs). They must understand how to set up machines accurately to produce parts as per the drawing specifications.

CNC Machining

Modern machinists often operate CNC machines. This involves understanding G-code and M-code programming, setting up tooling and workpieces, and monitoring the automated machining process. CNC machines offer high precision, repeatability, and efficiency for mass production.

Metrology and Quality Control

Metrology is the science of measurement. Machinists use sophisticated measuring instruments like coordinate measuring machines (CMMs), optical comparators, and precision gauges to ensure parts meet quality standards and tolerances.

Materials Science

Machinists need a basic understanding of different engineering materials (steels, alloys, plastics) and how their properties affect machinability. Heat treatment processes can also influence the material's characteristics.

Wireman Trade

The Wireman trade focuses on the installation, maintenance, and repair of electrical wiring systems in buildings, industrial plants, and other structures. This includes domestic, commercial, and industrial wiring, conduit bending, cable jointing, and troubleshooting electrical faults in wiring circuits.

Electrical Wiring Systems

This covers different types of wiring installations, including concealed wiring (in conduits embedded in walls) and surface wiring (using conduits or trunking on surfaces). Understanding wiring layouts, circuit diagrams, and the selection of appropriate cables, conduits, and accessories is crucial.

Conduit Bending and Installation

Conduits (metal or PVC pipes) protect wiring. Wiremen need skills in accurately bending conduits to follow building contours and connect to junction boxes, using tools like conduit benders.

Wiring Accessories and Components

Knowledge of switches (one-way, two-way, intermediate), sockets, junction boxes, distribution boards, MCBs (Miniature Circuit Breakers), MCCBs (Molded Case Circuit Breakers), and RCDs (Residual Current Devices) is essential for safe and functional installations.

Cable Jointing and Termination

This involves connecting different lengths of cables or terminating cables into equipment. Techniques include using crimp connectors, soldering, and specialized jointing kits, ensuring secure and insulated connections.

Earthing and Safety

Proper earthing (grounding) of the entire installation is a critical safety aspect. Wiremen must understand earthing electrode types, conductor sizes, and earthing continuity requirements as per Indian Electricity Rules and IS standards. Safety procedures during installation, like de-energizing circuits and using PPE, are mandatory.

Testing and Troubleshooting

After installation, wiring systems must be tested for continuity, insulation resistance (using a megger), and proper functioning of safety devices like RCDs. Troubleshooting involves identifying and rectifying faults such as short circuits, open circuits, or earthing failures in the wiring.

Welder Trade

The Welder trade involves joining metal parts using various welding techniques. This requires understanding different welding processes, metal properties, safety procedures, and the ability to produce strong, sound welds.

Welding Processes

Key welding processes include:

• Arc Welding (SMAW - Shielded Metal Arc Welding): Uses a consumable electrode coated with flux. Common for general fabrication.
• Gas Welding (Oxy-Acetylene Welding): Uses a flame produced by burning acetylene and oxygen. Also used for brazing and cutting.
• MIG/MAG Welding (GMAW - Gas Metal Arc Welding): Uses a continuous wire electrode and a shielding gas. Faster than SMAW.
• TIG Welding (GTAW - Gas Tungsten Arc Welding): Uses a non-consumable tungsten electrode and a shielding gas. Produces high-quality welds, suitable for thin materials and exotic metals.
• Resistance Welding: Uses heat generated by electrical resistance (e.g., spot welding).

Understanding the principles, equipment, and applications of each process is vital.

Welding Equipment and Accessories

This includes welding machines (power sources), electrodes, filler rods, shielding gases, welding torches, regulators, hoses, and welding accessories like clamps and positioners.

Welding Techniques and Positions

Welders must master techniques for creating different types of joints (butt, lap, T, corner) and performing welds in various positions (flat, horizontal, vertical, overhead). Each position presents unique challenges and requires specific electrode angles and travel speeds.

Weld Quality and Defects

A good weld should be strong, free from defects like porosity (gas pockets), cracks, lack of fusion (incomplete joining), and slag inclusions. Welders need to know how to identify these defects and adjust their technique to avoid them. Visual inspection and destructive/non-destructive testing methods are used to assess weld quality.

Safety Practices

Welding involves significant hazards: intense UV radiation (eye and skin burns), sparks and hot metal (fire risk), fumes (respiratory hazards), and electrical shock. Proper PPE (welding helmet with appropriate shade, gloves, apron, safety shoes), ventilation, and fire prevention measures are essential.

Refrigeration and Air Conditioning (R&AC) Mechanic

The R&AC Mechanic trade deals with the installation, maintenance, and repair of refrigeration and air conditioning systems. This involves understanding thermodynamics, refrigeration cycles, components like compressors, condensers, evaporators, and refrigerants.

Basic Principles of Refrigeration and Air Conditioning

Refrigeration is the process of removing heat from a space to lower its temperature. Air conditioning involves controlling temperature, humidity, and air purity. Key concepts include heat transfer, specific heat, latent heat, and the laws of thermodynamics.

Refrigeration Cycle

The vapor-compression refrigeration cycle is fundamental. It involves four main components:

• Compressor: Compresses the refrigerant vapor, increasing its pressure and temperature.
• Condenser: Rejects heat from the high-pressure refrigerant, causing it to condense into a high-pressure liquid.
• Expansion Valve (or Capillary Tube): Reduces the pressure and temperature of the liquid refrigerant.
• Evaporator: Absorbs heat from the space to be cooled, causing the low-pressure refrigerant to evaporate into a low-pressure vapor.

Understanding the P-h (Pressure-Enthalpy) and T-s (Temperature-Entropy) diagrams is helpful for analyzing the cycle.

Refrigerants

Refrigerants are working fluids that absorb and release heat. Common types include CFCs (e.g., R-12), HCFCs (e.g., R-22), HFCs (e.g., R-134a, R-410A), and natural refrigerants (e.g., ammonia, CO2, hydrocarbons). Environmental regulations (like the Montreal Protocol) have led to the phase-out of ozone-depleting substances. Knowledge of refrigerant properties, handling, and safety is crucial.

Components and Systems

This includes various types of compressors (reciprocating, rotary, scroll), condensers (air-cooled, water-cooled), evaporators (direct expansion, flooded), fans, motors, filters, and controls (thermostats, pressure switches).

Installation and Maintenance

Proper installation involves correct sizing of equipment, pipework, vacuuming the system, and charging with the correct amount of refrigerant. Maintenance includes cleaning coils, checking refrigerant levels, lubricating motors, and inspecting electrical connections.

Troubleshooting and Repair

Common issues include loss of cooling, strange noises, system leaks, and electrical faults. Troubleshooting involves checking pressures, temperatures, electrical circuits, and component performance using tools like manifold gauges, vacuum pumps, leak detectors, and multimeters.

General Safety and Workshop Practices

Across all trades, a strong emphasis on safety and good workshop practices is paramount. This ensures the well-being of the worker, the longevity of equipment, and the quality of work.

Personal Protective Equipment (PPE)

PPE is the last line of defense against workplace hazards. Essential items include:

• Safety Glasses/Goggles: Protect eyes from flying debris, sparks, and chemical splashes.
• Gloves: Protect hands from cuts, abrasions, heat, cold, and chemicals. Type varies by task (e.g., leather for welding, insulated for electrical work).
• Safety Shoes: Protect feet from falling objects and provide good grip.
• Aprons/Overalls: Protect clothing and skin from dirt, sparks, and chemicals.
• Hearing Protection: Earplugs or earmuffs in noisy environments.
• Respirators/Masks: Protect against dust, fumes, and vapors.

Fire Safety

Understanding fire prevention and response is crucial. This includes:

• Knowing the types of fire extinguishers (Class A, B, C, D, K) and their appropriate uses.
• Keeping the workspace clean and free of flammable materials.
• Proper handling of flammable liquids and gases.
• Awareness of emergency exits and assembly points.

Workshop Housekeeping

A clean and organized workshop is a safe workshop. This involves:

• Keeping floors clear of obstructions, spills, and debris.
• Storing tools and materials properly in designated locations.
• Regular cleaning of machinery and work areas.
• Proper disposal of waste materials.

Machine Safety

All machinery should be operated with guards in place. Workers must be trained on the specific machine they are operating and follow operating procedures. Never bypass safety interlocks or attempt repairs without proper authorization and de-energization.

Electrical Safety

For trades involving electricity, strict adherence to safety protocols is non-negotiable. This includes:

• Never working on live circuits unless absolutely necessary and with proper precautions.
• Using insulated tools.
• Ensuring proper earthing of equipment.
• Understanding lockout/tagout procedures to prevent accidental startup during maintenance.