UPMSP High School Electrician cheat sheet

Ohm's law: V = I × R; power P = V × I = I²R = V²/R.

Series circuit: R_total = R1 + R2 + …; same current through all elements; voltage divides in proportion to resistance.

Parallel circuit: 1/R_total = 1/R1 + 1/R2 + …; same voltage across all branches; current divides inversely with resistance.

Kirchhoff's current law: algebraic sum of currents at a node is zero; voltage law: algebraic sum of voltages around a closed loop is zero.

AC sine wave: RMS value = peak/√2 ≈ 0.707 × peak; average value = 0.637 × peak; frequency f = 1/T.

Conductor resistance R = ρL/A; ρ_copper ≈ 1.72 × 10⁻⁸ Ω·m at 20 °C; resistance rises with temperature for metals.

Electrical shock severity depends on current through the body; 30 mA can cause respiratory paralysis, and 50 mA can cause ventricular fibrillation.

First aid for electric shock: isolate supply, do not touch the casualty until supply is off, call for help, begin CPR if breathing has stopped.

Wire size selection depends on current-carrying capacity, voltage drop (typically ≤ 3% for a final circuit), and ambient temperature derating.

Indian cable colour convention for single-phase: phase red or brown, neutral black or blue, earth green or green-yellow.

PVC conduit wiring is preferred in damp locations and for concealed work; batten wiring uses cleats and is suitable for dry indoor surfaces.

A two-way switch has three terminals (common, L1, L2); two two-way switches wired with a three-core cable control one lamp from two positions.

A staircase circuit uses two two-way switches; an intermediate switch is added for control from three or more positions.

Cable insulation resistance is measured with a megger at 500 V DC; a minimum value of 1 MΩ is commonly required for a low-voltage installation.

Flexible cords are rated by conductor cross-section and number of cores; a 3-core cord is used for Class I appliances requiring an earth connection.

Bending radius of a cable should not be less than the manufacturer's minimum, typically 6–12 times the cable diameter depending on type.

Transformer EMF equation: E = 4.44 × f × N × Φm; turns ratio N1/N2 = V1/V2 = I2/I1 for an ideal transformer.

A transformer works only on AC; it transfers energy by mutual induction and does not change frequency.

DC motor back EMF: Eb = V − IaRa; torque T ∝ ΦIa; shunt motor speed falls slightly with load, series motor speed falls sharply.

Three-phase induction motor synchronous speed Ns = 120f/P; slip s = (Ns − Nr)/Ns; rotor frequency = s × supply frequency.

A capacitor-start single-phase induction motor uses a capacitor in the starting winding to create phase displacement and starting torque.

Alternator frequency f = PN/120, where P is the number of poles and N is speed in rpm.

Motor protection: overload relay protects against sustained overcurrent; fuse or MCB protects against short circuit; no-volt release prevents restart after supply failure.

Star-delta starter reduces starting current to one-third of the direct-on-line value and is used for delta-connected motors.

Ammeter is connected in series and has very low resistance; voltmeter is connected in parallel and has very high resistance.

A shunt resistor extends ammeter range; a series multiplier resistor extends voltmeter range.

A megger (insulation resistance tester) applies a high DC voltage and measures resistance in megohms; never use it on a live circuit.

A multimeter in continuity mode indicates a closed circuit by a beep; in resistance mode it must be used with the circuit de-energised.

Clamp meter measures current without breaking the circuit by sensing the magnetic field around a single conductor.

Energy meter (kWh meter) constant is the number of revolutions per kWh; energy = (revolutions × 3600) / (constant × time in seconds).

Wheatstone bridge measures unknown resistance by balancing two legs; it is accurate for medium resistance values.

Instrument accuracy class indicates maximum error as a percentage of full-scale deflection; a 1.0 class meter has ±1% full-scale error.

Domestic single-phase supply in India is 230 V, 50 Hz; three-phase industrial supply is 415 V, 50 Hz.

Lighting sub-circuit load is commonly limited to 800 W or 10 points; power sub-circuit uses 16 A or 20 A outlets.

Estimation steps: prepare layout, count points, calculate cable length with 10–15% wastage, list accessories, then apply labour and overhead percentages.

A distribution board should be located near the entry point and at a height of about 1.5 m for ease of operation.

Socket outlets in wet areas must be protected by a 30 mA RCD (ELCB) and installed at least 1.2 m above floor level.

Load calculation for a domestic installation: sum connected loads, apply diversity factor, then select main switch and cable size.

Industrial motor feeder cable size is selected from full-load current, derated for ambient temperature and grouping, then checked for voltage drop.

Earthing conductor size for a domestic installation is typically half the phase conductor size, subject to a minimum of 1.5 mm² copper.

Fuse rating should be slightly above normal load current but below the cable current-carrying capacity.

MCB trips on overload (thermal) and short circuit (magnetic); its rated breaking capacity must exceed the prospective fault current.

ELCB/RCD with 30 mA sensitivity protects people against earth leakage; it does not protect against overload or short circuit.

Earthing resistance for domestic installations should be as low as practicable; a value below 1 Ω is good, and above 5 Ω usually needs improvement.

Plate earthing uses a copper or GI plate buried vertically with charcoal and salt; pipe earthing uses a GI pipe of about 38 mm diameter.

Earth wire must be connected to the metal body of appliances and must never be fused or switched.

Portable electrical tools should be used with a 30 mA RCD and inspected for damaged insulation before use.

Lockout/tagout: isolate the supply, lock the switch, attach a warning tag, verify dead with a tester, then work.

Copper has lower resistivity than aluminium but higher cost and density; aluminium is used for overhead lines and large feeders.

PVC is used for insulation and conduit because it is flexible, flame-retardant, and moisture-resistant; it softens at high temperature.

Porcelain and glass are used for insulators because of high dielectric strength and low moisture absorption.

Silicone and mica insulation are chosen for high-temperature applications such as irons and heaters.

Tools: combination pliers for gripping and cutting, side-cutting pliers for wire cutting, nose pliers for bending in confined spaces, wire stripper for removing insulation without nicking the conductor.

A test lamp or voltage tester confirms presence of supply; a screwdriver with an insulated handle is mandatory for live work.

Soldering iron wattage: 25–40 W for electronic joints, 65–100 W for heavier lugs and terminals.

Crimping tools produce gas-tight joints on lugs; the correct die size must match the lug and conductor size.

Luminous flux is measured in lumens (lm); illuminance is measured in lux (lm/m²); 1 lux = 1 lumen per square metre.

Illuminance required: living rooms about 100–150 lux, offices 300–500 lux, workshops 300–500 lux, precision work 750–1000 lux.

Incandescent lamp efficacy is about 10–15 lm/W; CFL is 50–70 lm/W; LED is 80–120 lm/W or more.

Luminous efficacy = luminous flux / electrical power input, expressed in lumens per watt.

Heating element resistance R = V²/P; a 1000 W, 230 V element draws about 4.35 A and has resistance of about 53 Ω.

Nichrome is used for heating elements because of high resistivity, oxidation resistance, and ability to withstand high temperature.

Induction heating relies on eddy currents in the workpiece; dielectric heating relies on molecular friction in a non-conducting material.

A fluorescent lamp needs a choke or electronic ballast to limit current and a starter to preheat the electrodes.

Before making a joint, strip insulation to the required length without nicking the conductor; clean the conductor with emery cloth.

Britannia joint is used for straight overhead conductors; western union joint is used for stranded conductors; married joint is used for small wires.

Soldering sequence: clean, apply flux, heat the joint, apply solder, allow to cool without disturbing the joint.

Continuity test: set multimeter to continuity or low resistance range, confirm near-zero reading across the intended path.

Polarity test on a socket: phase on the right, neutral on the left, earth at the top (viewed from the front).

Insulation resistance test: disconnect load and supply, connect megger between phase and earth, apply 500 V DC for one minute, read resistance.

Drill speed and bit selection: harder material needs lower speed and higher pressure; use coolant when drilling metal.

Bench work safety: secure the workpiece in a vice, wear goggles when cutting or drilling, and keep the work area clear.

A resume for an electrician should list qualifications, practical skills, safety training, and any licences or certifications.

A job application letter includes sender's address, date, recipient's address, subject line, salutation, body, and closing.

An invoice must show seller details, buyer details, invoice number and date, description of work, quantity, rate, tax, and total amount.

A quotation is an offer to supply at a stated price; it is not a bill, and it should state validity period and terms.

Entrepreneurship requires identifying a market need, estimating cost, pricing, arranging finance, and complying with GST and local licensing.

GST registration is required in India when turnover exceeds the threshold prescribed for the state; an electrician must charge GST on taxable services.

Workplace communication should be clear, brief, and respectful; written instructions and checklists reduce errors on site.

Safety communication: report hazards immediately, use warning signs and barricades, and record accidents in the accident register.