Maharashtra SSC Electrical & Hardware Installation Tech Pre-Voc/NSQF cheat sheet

Electric shock severity depends on current through the body, path, and duration: roughly 1 mA is perceptible, 10-30 mA causes muscle tetany (inability to let go), and 50 mA and above across the heart can cause ventricular fibrillation.

Body resistance dry skin is about 100,000 ohm; wet or broken skin can fall to about 1,000 ohm, so the same voltage becomes far deadlier in wet conditions.

Rule of thumb: currents above about 30 mA are treated as potentially fatal; earth-leakage protection is set near this threshold for human protection.

First aid sequence for a shock victim: isolate the supply, do not touch the casualty while still in contact with live parts, call for help, check breathing and pulse, begin CPR if trained, and place an unconscious breathing casualty in the recovery position.

For electrical burns, cool the area with clean running water for about 10-20 minutes, do not burst blisters or apply oil, and always send the casualty for medical review because internal injury may exceed visible burns.

Fire classes: Class A solid combustibles (water, foam), Class B flammable liquids (foam, CO2, dry powder), Class C gases, Class D metals, and electrical fires use CO2 or dry powder only, never water or foam.

Lockout/tagout rule: isolate the circuit, lock the isolator, attach a warning tag with the holder's name, prove dead with a tester on all conductors, then discharge and earth before work.

Personal protective equipment for electrical work: insulating gloves tested to the working voltage, helmet, safety footwear, arc-rated clothing, and insulated tools; PPE supplements safe isolation, it never replaces it.

Portable ladder rule: metal ladders are prohibited near live conductors; use wooden or fibreglass ladders and maintain the statutory clearance from overhead lines.

Ohm's law: V = I x R, I = V / R, R = V / I, where V is in volts, I in amperes, R in ohms.

DC power: P = V x I = I squared x R = V squared / R, in watts.

Single-phase AC: apparent power S = V x I in volt-amperes; real power P = V x I x cos(phi) in watts; reactive power Q = V x I x sin(phi) in var.

Three-phase power: P = square root of 3 x V(line) x I(line) x cos(phi); at unity power factor P equals 1.732 x V x I.

Series circuit: current is the same in all elements, voltages add, total resistance R = R1 + R2 + ...; voltage divides in proportion to resistance.

Parallel circuit: voltage is the same across all branches, currents add, and total resistance is given by 1/R = 1/R1 + 1/R2 + ...; for two resistors R = R1R2/(R1+R2).

Energy is power x time: 1 kWh = 1000 W for 1 hour = 3.6 x 10^6 joules; an electricity bill is charged on kWh units.

Conductor resistance R = rho x L / A: resistance rises with length and resistivity, falls with cross-sectional area; temperature rise increases resistance of metals.

Kirchhoff's laws: at any node the sum of currents entering equals the sum leaving; around any closed loop the algebraic sum of voltages is zero.

Copper resistivity is about 0.0172 ohm-mm squared per metre; aluminium is about 0.0282, roughly 1.6 times higher, so aluminium needs a larger area for the same current.

Annealed copper is the standard reference conductor (100% IACS conductivity); aluminium is lighter and cheaper but needs anti-oxidant paste and bimetallic connectors at joints.

Common insulators and their limits: PVC about 70 degrees C, XLPE about 90 degrees C, rubber flexible cables about 60 degrees C; class ratings for motor insulation run Y=90, A=105, E=120, B=130, F=155, H=180 degrees C.

Cable size is chosen by three checks: current-carrying capacity, permissible voltage drop (about 3% for domestic final circuits), and short-circuit withstand.

Standard flexible cable cores use colour coding: old Indian practice red/yellow/blue for phases, black for neutral, green for earth; IEC practice brown phase, blue neutral, green-yellow earth.

Wiring accessories: a switch is rated by current and voltage (for example 6 A or 16 A, 240 V); a socket outlet is rated the same way; a ceiling rose provides the loop-in termination for a light.

A two-way switch has three terminals (common, L1, L2) and is used in pairs for staircase lighting; an intermediate switch has four terminals for three-point control.

A miniature circuit breaker is marked with rated current (In), trip curve (B, C, D) and breaking capacity in kA; a fuse is marked with rated current and voltage.

Conduit and casing: PVC conduit is used for concealed wiring, steel conduit provides mechanical protection and earthing continuity, and casing-and-capping is used for surface wiring.

Insulated hand tools must carry a voltage marking (commonly 1000 V) and be visually inspected before use; cracked insulation means the tool is withdrawn from service.

A screwdriver must match the slot or recess size; a loose fit slips and damages the screw head, and a screwdriver must never be used as a chisel or pry bar.

Pliers: combination pliers for gripping and cutting, long-nose pliers for reaching into boxes, side cutters for wire cutting, and wire strippers set to the conductor size to avoid nicking copper.

A multimeter measures voltage in parallel with the load and current in series; measuring voltage while the meter is set to current or resistance range can blow the internal fuse or damage the meter.

Continuity and resistance tests are done with the circuit dead; an insulation resistance test uses a megger at 500 V DC for LV circuits and expects at least 1 megohm.

A clamp meter measures current by surrounding one conductor only; clamping a cable carrying live and neutral together reads near zero because the fields cancel.

A megger (insulation resistance tester) is never used on a live circuit or on equipment containing electronics without disconnection, because its test voltage can destroy components.

An earth tester measures earth electrode resistance; a socket tester checks polarity and earth presence but does not prove insulation quality.

Calibration and range: always start on the highest range for an unknown quantity, and check the meter's CAT rating against the circuit's overvoltage category before measuring.

Domestic supply in India is single-phase 230 V, 50 Hz with three wires: phase (live), neutral and earth; three-phase 400 V is used where loads demand it.

Final circuits are separated: lighting circuits typically 5-6 A, socket circuits 16 A, and fixed appliances such as geysers and air conditioners on dedicated circuits.

Protection is coordinated from the supply end: service fuse or main breaker, then energy meter, then main switch, then residual current device, then individual MCBs for each circuit.

An MCB protects against overload and short circuit; an RCCB or RCD protects people against earth leakage and is rated by sensitivity (30 mA for personal protection, 100-300 mA for fire protection).

An MCB does not protect against earth leakage and an RCD does not protect against overload; an RCBO combines both functions in one device.

Earthing systems: pipe earthing and plate earthing are common in India; earth wire size for a circuit is generally half the phase conductor up to a limit, and earth resistance should be as low as practicable (commonly 1 ohm for substations, a few ohms for domestic).

Wiring system choices: cleat wiring for temporary work, casing-and-capping and conduit for permanent surface or concealed work, and batten or conduit for lighting points.

A staircase circuit uses two two-way switches at the ends and, if a third control point is needed, an intermediate switch between them.

A bell circuit uses a push button in series with the bell and a step-down transformer or bell battery; the push button is a momentary make contact.

Screw sizing: the first number is the gauge (diameter) and the second is length in millimetres, for example 8 x 50 means gauge 8, 50 mm long; wood screws are tapered, machine screws are parallel.

Rawl plugs and wall anchors are selected by the screw gauge and the base material: plastic anchors for brick and plasterboard, metal anchors for concrete and heavy loads.

A wall plug hole should be drilled to the plug diameter and slightly deeper than the plug; the screw must engage the full plug length, not bottom out in the hole.

Fastener materials: zinc-plated steel for indoor dry use, stainless steel for damp or outdoor locations, and brass for decorative or corrosive environments.

A masonry drill bit with a hammer action is used for concrete; the bit diameter must equal the plug or anchor diameter, and drilling near an edge risks breakout.

Fixture mounting: ceiling fans and heavy luminaires need a hook or bracket fixed to the structural slab or a rated anchor, never to plasterboard alone; the fan hook must carry the fan's weight with margin.

Torque rule: over-tightening shears screws and cracks plugs, under-tightening leaves joints loose; a loose electrical terminal heats and can start a fire.

Level and plumb: switch and socket boxes are set at consistent heights (commonly 1200-1300 mm for switches, 300 mm for sockets in Indian practice) using a spirit level and plumb line.

Cable routing: cables are run in straight lines, horizontally or vertically, with at least 50 mm clearance from gas and water pipes, and are never buried diagonally where a drill could hit them.

A heating appliance such as an iron, geyser or heater is essentially a resistive element: power P = V squared / R, so element resistance sets the wattage at a given supply voltage.

A fan motor is an induction motor with a capacitor in the auxiliary winding; failure to start with a humming sound commonly means a failed capacitor or a seized bearing.

A mixer grinder uses a universal (brush) motor; sparking at the brushes, loss of speed or a burning smell points to worn brushes, a shorted field coil or a faulty speed regulator.

An electric iron with a thermostat cycles the element on and off to hold temperature; a faulty thermostat gives no heat or uncontrolled overheating, and the sole plate must be cleaned only when cold.

Preventive maintenance schedule: inspect plugs and cords for damage, tighten terminal screws, clean vents and filters, check earthing continuity, and test the RCD trip function periodically.

Motor maintenance: keep windings dry and clean, check insulation resistance with a megger, lubricate bearings per schedule, and verify the cooling fan and terminal box gasket.

A capacitor start capacitor run motor has two capacitors; a bulged or leaking capacitor must be replaced with the same microfarad value and voltage rating, never a lower voltage.

Wiring a plug: connect live to the live pin, neutral to neutral, earth to the earth pin; the earth conductor is left longer so it is the last to be pulled out under strain.

Fault finding sequence: confirm supply, check fuse or breaker, check plug and cord continuity, check the switch, then the appliance; isolate before every step.

Standard symbols: a circle with a cross is a lamp, a circle with an M is a motor, a rectangle with a diagonal is a resistor, and two parallel plates are a capacitor.

A switch symbol drawn open means the normal (de-energised) state; a push button is drawn as a momentary contact, normally open or normally closed.

Earth is drawn as three decreasing horizontal lines or a circle with an earth symbol; the protective earth conductor is identified by green-yellow.

A schematic (circuit) diagram shows electrical connections without regard to physical position; a wiring diagram shows the actual terminal-to-terminal connections; an installation or layout plan shows physical positions on the building plan.

Single-line diagrams are used for power distribution, showing the source, main switch, meter, distribution board and outgoing circuits on one line.

Ladder or line diagrams read left to right with the live rail at the top and neutral at the bottom; each rung is one control circuit.

Terminal marking: in a contactor, A1 and A2 are the coil, and the main contacts are numbered 1-2, 3-4, 5-6; the auxiliary normally open contact is 13-14 and normally closed is 21-22.

Drawing conventions: conductors are drawn as straight horizontal or vertical lines, joints are shown as dots, and crossing lines without a dot are not connected.

A distribution board schedule lists each circuit's rating, cable size and purpose, and must match the physical board labelling.

A curriculum vitae for a technician lists trade qualification (for example NSQF level or ITI), practical skills, tools handled, safety training and any apprenticeship, with dates and employers.

A job application and covering letter follow a formal structure: sender details, date, recipient, subject line, body stating the post applied for and suitability, closing and signature.

Interview behaviour: arrive early, carry original certificates, answer with specific examples of work done, and ask clarifying questions about the role and safety responsibilities.

Workplace communication uses clear, short instructions and confirms understanding by repeating back; written handover notes record the work done, the isolation applied and any pending faults.

Teamwork and escalation: report hazards and near misses immediately to the supervisor, record them, and never bypass a safety rule to meet a deadline.

Entrepreneurship basics: a small electrical contracting business needs a costing sheet covering material, labour, travel and overhead, plus a margin, before quoting a job.

Statutory and licensing awareness: electrical contracting in India requires a licence under the Central Electricity Authority regulations, and GST registration applies above the turnover threshold.

Customer relations: give a written estimate, explain the fault in plain language, provide a bill with material and labour separated, and honour the warranty period.

Record keeping: maintain an invoice book, a stock register for tools and material, and a job register; these support loan applications and repeat business.

Rescue rule: switch off the supply first; if that is impossible, use an insulated object to separate the casualty from the conductor, and never grasp the casualty with bare hands.

Cardiopulmonary resuscitation for an adult: 30 chest compressions at 100-120 per minute to a depth of 5-6 cm, then 2 rescue breaths; continue until help arrives or the casualty recovers.

Recovery position is used for an unconscious casualty who is breathing normally; it keeps the airway open and prevents choking on vomit.

Burns first aid: cool with clean running water, cover with a sterile non-stick dressing, do not apply ice, oil or toothpaste, and do not remove clothing stuck to the burn.

Fire extinguisher use follows PASS: Pull the pin, Aim at the base of the fire, Squeeze the handle, Sweep side to side; electrical fires use CO2 or dry powder only.

Emergency numbers in India: 112 for the all-in-one emergency helpline, 108 for ambulance, and 101 for fire; display these numbers at the workplace.

Housekeeping and 5S: sort, set in order, shine, standardise, sustain; a clean work area reduces trips, cuts and tool loss.

Manual handling rule: bend the knees, keep the load close to the body, do not twist while lifting, and use a trolley for heavy items such as cable drums.

Near-miss reporting is mandatory practice: a near miss is a warning of a future accident and must be recorded and investigated even when no injury occurred.

Frequency in India is 50 Hz, so one cycle lasts 20 ms and the RMS value of a sine wave is peak divided by square root of 2, about 0.707 of peak.

Inductive reactance X_L = 2 x pi x f x L and capacitive reactance X_C = 1 / (2 x pi x f x C), both in ohms.

Impedance Z = square root of (R squared + (X_L - X_C) squared); at resonance X_L equals X_C and Z equals R, giving unity power factor.

Power factor cos(phi) = P / S; a low power factor draws more current for the same real power, so capacitors are added in parallel to correct it.

In a purely inductive circuit current lags voltage by 90 degrees; in a purely capacitive circuit current leads voltage by 90 degrees; in a resistive circuit they are in phase.

Star and delta: in star, line voltage equals square root of 3 times phase voltage and line current equals phase current; in delta, line current equals square root of 3 times phase current and line voltage equals phase voltage.

A transformer changes voltage in the ratio of turns: V1/V2 = N1/N2, and power is approximately constant, so current changes inversely with voltage.

Instrument transformers: a current transformer steps current down for measurement (for example 100/5 A) and its secondary must never be open-circuited while energised.

Energy meter constant is revolutions per kWh; it is used to check accuracy by timing a known number of revolutions against a known load.

Cable current-carrying capacity depends on installation method: the same cable carries less current in conduit in a wall than clipped in free air, so the derating factor must be applied.

Voltage drop calculation for a single-phase circuit: V_drop = 2 x I x L x rho / A, using the total out-and-back length; keep it within the permitted percentage.

A distribution board is fed from the main switch and divided into outgoing ways; each way has its own MCB rated for the cable it protects, not for the appliance.

Discrimination rule: the upstream device must have a higher rating and slower time-current characteristic than the downstream device so a fault trips only the nearest breaker.

Short-circuit current is limited by the source impedance and the cable impedance; the breaker's breaking capacity in kA must exceed the prospective fault current.

Earthing conductor continuity must be verified after installation; a broken earth path leaves the appliance casing live if a fault occurs.

Testing sequence for a new installation: visual inspection, continuity of protective conductors, insulation resistance, polarity, earth electrode resistance, then functional test of RCDs and breakers.

A residual current device is tested with its built-in test button and by an independent RCD tester; the test button only proves the trip mechanism, not the earthing path.

Lighting circuits are wired loop-in at the ceiling rose, with the switch in the phase conductor only; switching the neutral is a defect because the lamp stays live when off.

Anchor pull-out strength depends on base material, embedment depth and hole cleanliness; blow the dust out of a drilled hole before inserting a chemical or mechanical anchor.

A chemical anchor uses a resin capsule or cartridge; it needs the full curing time at the ambient temperature before any load is applied.

A toggle or spring-tog anchor is used for hollow walls and plasterboard; it spreads the load over a large area behind the board.

A self-drilling screw is used for sheet metal and light sections; a self-tapping screw forms its own thread in plastics and thin metal.

A bolt and nut joint needs a washer under the nut and, where vibration exists, a spring washer or thread-locking compound to prevent loosening.

A conduit saddle or clip is spaced according to conduit size, commonly about 1 m for 20 mm conduit on horizontal runs, with a clip within 300 mm of every box or bend.

A junction box must remain accessible after installation; it is never buried in plaster or concrete without an inspection cover.

Ceiling fan installation: the hook must be embedded in the slab or a rated anchor, the down-rod length sets the blade height (commonly 2.1-2.4 m above the floor), and the fan must be earthed.

A switch box is set plumb and flush with the finished wall surface; the plaster ring and plate must sit flat without gaps.

Before repairing any appliance, unplug it, discharge capacitors in the power supply, and confirm dead with a tester on all terminals.

Heating element test: measure resistance with a multimeter; a good element reads a low finite resistance, an open element reads infinity, and a shorted element reads near zero.

Earth continuity test on an appliance: measure between the earth pin of the plug and the metal casing; the reading must be near zero ohm.

Insulation resistance test on an appliance: apply 500 V DC between live/neutral joined and the casing; the reading must be at least 1 megohm to pass.

A cord grip in a plug or appliance must clamp the outer sheath, not the individual cores; the earth conductor is left longer than live and neutral.

Fuse replacement must match the original current rating and type (fast or time-lag); a higher-rated fuse defeats protection and risks fire.

Carbon brushes in a universal motor are replaced in pairs, and the commutator is cleaned and checked for burning or grooving when brushes are changed.

A thermostat is tested for continuity at room temperature and for open circuit when heated; a thermal fuse is a one-shot device and cannot be reset.

After any repair, perform a functional test and a leakage test before returning the appliance to the customer, and record the test results.

A contactor coil symbol is a rectangle with a diagonal line, marked with the coil reference; the contacts it operates are drawn elsewhere and identified by the same reference letter.

A relay contact is drawn in its de-energised position, and the contact is labelled with the coil it belongs to (for example K1).

A normally open contact closes when the coil is energised; a normally closed contact opens; the drawing convention is always the unenergised state.

A timer symbol shows a clock face or a semicircle with an arrow; an on-delay timer contact changes state after the set time when the coil is energised.

A thermal overload relay symbol is a rectangle with a bimetal element marking, with contacts 95-96 normally closed and 97-98 normally open.

A motor symbol is a circle with M; the terminal box connections for star and delta are shown as six terminals U1 V1 W1 and W2 U2 V2.

A wiring diagram for a two-way staircase circuit shows the phase looped through the common of the first switch, the two strappers between L1-L1 and L2-L2, and the second common feeding the lamp.

A layout plan uses a scale and shows the building outline, conduit routes, switch and socket positions, and the distribution board location with a legend.

Drawing standards: keep line weights consistent, label every component with a reference, include a title block with drawing number, scale, date and revision.

Digital tools for a technician: a smartphone for job photos, a messaging app for customer coordination, a spreadsheet for quotations, and an online payment app for collection.

A quotation is not a bill: a quotation is an offer with validity period, a bill is a demand for payment after work, and an estimate is an approximate indication of cost.

Basic costing: total cost = material + labour + travel + overhead; selling price = total cost / (1 - margin percentage) when margin is expressed on selling price.

Cash flow rule: collect a part advance on large jobs, bill promptly on completion, and keep a separate account for business and personal money.

Written communication: an email or message should state the purpose in the subject, keep the body short with numbered points, and end with a clear action and deadline.

Active listening in a customer conversation: let the customer finish, repeat the problem back, confirm the appointment time, and record the details in the job register.

A safety talk or toolbox meeting is a short, documented briefing before work begins, covering the hazards of the day and the controls to be used.

Financial literacy: understand the difference between a loan and a subsidy, check interest rate and repayment period, and keep receipts for every business purchase.

Growth path for a technician: apprenticeship, skilled worker, supervisor, then self-employed contractor; each step needs a record of work and a reference.

Cable construction: conductor, insulation, bedding, armouring and outer sheath; armoured cable is used where mechanical damage is possible and the armour is earthed.

Stranded conductors are used for flexibility and for larger sizes; solid conductors are used for fixed wiring up to about 2.5 mm squared.

Cable jointing: strip insulation to the correct length, clean the conductor, apply flux and solder or a proper crimp ferrule, then insulate with heat-shrink or insulation tape with 50% overlap.

A crimped joint needs the correct die and lug size; a loose crimp heats under load and is a common cause of fire at terminals.

Insulating tape is applied over the joint from the insulation onto the conductor and back, overlapping each turn by half the tape width.

Cable colour and identification: three-core flexible cable uses brown, blue and green-yellow; a cable with a green-yellow core must never be used as a live conductor.

A ceiling rose, batten holder and angle holder are rated for the lamp wattage; a high-wattage lamp in a low-rated holder overheats the holder.

A modular switch plate and frame system uses standard modules (for example 1, 2, 3, 4 module plates) so accessories can be combined in one plate.

A cable gland provides mechanical grip and ingress protection at the enclosure entry; the gland size must match the cable outer diameter.

A hacksaw blade is fitted with the teeth pointing forward and tensioned so it twangs; 18 teeth per inch is used for thick metal, 24-32 for thin sections and conduit.

A file cuts on the forward stroke only; a file is never used without a handle because the tang can pierce the hand.

A chisel is struck with a mallet, not a hammer, for wood; a cold chisel for metal is struck with a hammer and the head is kept free of mushrooming.

A drill bit is selected by material: HSS for metal, masonry for concrete, brad-point for wood; the drill speed is reduced for larger diameters and harder materials.

A spirit level is checked by placing it on a flat surface, noting the bubble, then turning it end for end; if the bubble moves, the level is out of adjustment.

A vernier caliper reads to 0.02 mm on a common 50-division scale; a micrometer reads to 0.01 mm; both are checked for zero error before use.

A steel rule is read with the eye directly above the mark to avoid parallax error; measurements are taken from a true edge, not a worn end.

Tool care: clean and oil tools after use, store them in a tool roll or box, never leave them on the floor or in a walkway, and replace damaged insulation immediately.

A torque screwdriver or wrench is used where the terminal manufacturer specifies a tightening torque; the value is recorded on the inspection sheet.

Circuit load calculation: total connected load in watts divided by 230 V gives current; apply a diversity factor because not all appliances run at once.

A geyser or air conditioner circuit is run as a dedicated radial circuit with its own MCB and, for a geyser, its own isolator switch outside the bathroom.

A bathroom is a special location: sockets are not installed inside the bathroom in ordinary practice, and all metal parts are bonded to the protective earth.

A kitchen circuit needs a higher-rated socket outlet for appliances such as a microwave or mixer, and the socket must be protected by an RCD.

A motor circuit uses a starter with overload protection; the MCB protects the cable, the overload relay protects the motor, and both are needed.

A bell or door chime circuit uses a step-down transformer to a safe voltage; the push button carries only the low-voltage circuit.

A socket outlet circuit is wired as a ring or radial depending on design; in Indian domestic practice radial circuits with 16 A sockets are common, protected by a 16 A or 20 A breaker.

Load balancing on a three-phase distribution board: distribute single-phase circuits across phases so the phase currents are approximately equal.

Before adding a new circuit, check the spare ways in the board, the main switch rating and the total connected load against the sanctioned load.

Conduit bending: a 20 mm PVC conduit is bent with a bending spring inserted in the bore, and the bend radius must be large enough not to damage the cable during pulling.

The number of bends between draw boxes is limited (commonly to two 90-degree bends or equivalent) so cables can be pulled without damage.

Conduit fill: cables should occupy no more than about 40% of the conduit internal cross-section to allow heat dissipation and pulling.

A draw wire is left in the conduit after installation to allow later cable pulling; the conduit ends are reamed and bushed to protect the cable sheath.

Steel conduit joints must be electrically continuous and bonded to earth; a PVC conduit does not provide an earth path, so a separate earth conductor is run.

Cable tray and ladder support spacing depends on the load and span; the tray is earthed at intervals and at every joint where continuity is not guaranteed by the joint.

A cable is never run through a structural beam without a sleeve or approval; a sleeve protects the cable and allows movement.

Fixing into a wall: identify the substrate first (concrete, brick, plasterboard), then choose the anchor; drilling into unknown material risks hitting a pipe or cable.

A ceiling rose or luminaire is supported independently of the cable; the cable must not carry the weight of the fitting.

A contactor is rated by its utilisation category (AC-1 for resistive loads, AC-3 for motor switching), coil voltage, and main contact current.

A thermal overload relay is set to the motor's full-load current; setting it too high removes protection and too low causes nuisance tripping.

A capacitor in a single-phase motor is rated in microfarads and volts AC; the replacement must match the capacitance and equal or exceed the voltage rating.

A diode allows current in one direction only; a bridge rectifier converts AC to DC and is tested by measuring forward and reverse resistance across its terminals.

A triac or thyristor is used for power control such as a fan regulator; a failed device gives no output or full output regardless of the control setting.

A limit switch is a mechanically operated contact used for position sensing; it is wired as normally open or normally closed depending on the control logic.

A solenoid valve or contactor coil is checked by measuring its resistance; an open coil reads infinity and a shorted coil reads near zero.

A printed circuit board fault is traced by checking supply voltages, then the oscillator or control IC, then the output stage; a swollen capacitor is replaced before further testing.

Spare parts must match the original rating and specification; substituting a lower-rated component is a common cause of repeat failure.

A direct-on-line starter diagram shows the main circuit (supply, MCB, contactor main contacts, overload relay, motor) and the control circuit (stop, start, holding contact, coil).

The holding or self-holding contact is wired in parallel with the start push button so the coil stays energised after the button is released.

A star-delta starter diagram shows three contactors (main, star, delta), a timer, and the motor's six terminals; the star contactor must open before the delta closes.

A forward-reverse starter uses two contactors with electrical interlocking (the normally closed auxiliary of one in the other's coil circuit) and often a mechanical interlock.

A limit switch in a control circuit is drawn in the position it occupies when the machine is at rest, and the drawing notes this convention.

A distribution board single-line diagram shows the incoming supply, main switch, meter, RCD, busbar and outgoing MCBs with their ratings and circuit descriptions.

A cable schedule lists each cable's tag, size, cores, route and length; it is used for material take-off and for testing.

A terminal wiring diagram shows the physical terminal numbers inside a panel; it is used for wiring and for fault finding, and must match the panel labels.

A legend on a drawing explains every symbol used; a drawing without a legend is incomplete for installation work.

Apprenticeship in India is governed by the Apprentices Act; an apprentice has a written contract, a stipend, and a defined training period and assessment.

Wages and working hours are governed by state and central labour law; a technician should know the minimum wage for the trade in the state and the overtime rule.

Provident fund and ESI registration apply to eligible establishments; the employer deducts the employee share and deposits it with the statutory authority.

Workplace rights include a safe workplace, training, protective equipment, and the right to refuse unsafe work without penalty.

A trade certificate and an NSQF level certificate are evidence of skill; they are presented at interviews along with a portfolio of work photographs and references.

A portfolio of completed jobs, with before and after photographs and a short description, is stronger evidence of skill than a verbal claim.

Self-employment options for a technician: repair shop, contracting for builders, maintenance contract for a housing society, or supply and installation of fittings.

Pricing a maintenance contract: estimate the number of visits, the labour hours per visit, the consumables and the travel, then add a contingency and a margin.

Customer complaint handling: listen, apologise for the inconvenience, state what will be done and when, do it, then confirm the customer is satisfied.

Arc flash hazard: an arc can reach several thousand degrees Celsius and cause severe burns; keep the correct distance, use arc-rated clothing, and never work on energised equipment without justification and a permit.

Approach distances and clearances from overhead lines are statutory; for low-voltage work the minimum approach distance is small but for high voltage it is measured in metres and must be confirmed from the supply authority.

Hazard identification: electrical, mechanical, chemical (battery acid), thermal, ergonomic and noise; each hazard needs a control before work starts.

Hierarchy of control: eliminate, substitute, engineer, administrate, then use PPE as the last line of defence.

A permit-to-work system records the isolation points, the earths applied, the person in charge and the validity period; work stops when the permit expires.

Portable electrical equipment is tested and tagged at intervals; a damaged plug, cracked casing or exposed conductor means the equipment is withdrawn from use.

Battery hazards: lead-acid batteries give off hydrogen, which is explosive; keep flames away, charge in a ventilated area, and use eye protection and acid-resistant gloves.

Confined space entry requires a risk assessment, atmospheric testing, a standby person and rescue arrangements; an electrical worker may encounter such spaces in trenches and pits.

Emergency response plan: know the exits, the assembly point, the first-aid box location and the isolation switch for the area before starting work.

Faraday's law: the induced EMF in a coil equals the rate of change of magnetic flux linkage; Lenz's law gives the direction opposing the change.

A current-carrying conductor produces a magnetic field; the field direction follows the right-hand grip rule, and the force on a conductor in a field follows Fleming's left-hand rule.

Heating effect: heat produced H = I squared x R x t joules, which is the basis of fuses, heaters and thermal overload relays.

Chemical effect: in electrolysis the mass deposited is proportional to the current and time (Faraday's laws of electrolysis); this underpins plating, cells and corrosion.

A cell converts chemical energy to electrical energy; its EMF is the open-circuit voltage and its internal resistance causes the terminal voltage to fall under load.

Cells in series add their EMFs and internal resistances; cells in parallel share the current and are used when a higher current is needed.

A capacitor stores charge Q = C x V and energy E = one half x C x V squared; it blocks DC and passes AC.

An inductor opposes change of current; its energy is E = one half x L x I squared, and it produces a back EMF when the current is interrupted.

A thermocouple produces a small EMF proportional to the temperature difference between two junctions; it is used for temperature measurement.

IP rating: the first digit is protection against solids (0-6) and the second against water (0-8); IP44 is splash-proof and suitable for bathrooms, IP65 is dust-tight and jet-proof.

An enclosure's IP rating applies only to the enclosure as installed; an unused gland hole left open defeats the rating.

Electrical accessories in damp areas need a rated enclosure, a gasket and a drain path; condensation inside a sealed box can still cause failure.

A distribution board is rated by its busbar current, the number of ways, and the IP rating; the board must be accessible and not in a bathroom or above a cooking range.

The earth bar in a distribution board must be separate from the neutral bar; bonding neutral to earth downstream of the supply point is a serious defect.

Cable insulation classes and temperature ratings determine the derating factor; a cable run through thermal insulation must be derated significantly.

Fire-rated cable is used for emergency lighting and fire alarm circuits so the circuit survives a fire for the specified period.

A metal enclosure must be earthed and have a reliable earth continuity path through all removable covers and gland plates.

A blanking plate closes an unused way in a distribution board to maintain the IP rating and prevent access to live parts.