Odisha CHSE +2 VOC-ITV Wireman Control Panel cheat sheet

Ohm's law: V = I × R; power P = V × I = I²R = V²/R. In a purely resistive DC circuit these three forms are interchangeable.

Series circuit: RT = R1 + R2 + …; current is common, voltage divides in proportion to resistance. Parallel circuit: 1/RT = 1/R1 + 1/R2 + …; voltage is common, current divides inversely with resistance.

Kirchhoff's laws: KCL - algebraic sum of currents at a node is zero; KVL - algebraic sum of voltages around a closed loop is zero.

AC quantities: RMS = peak/√2 ≈ 0.707 × peak; average of full sine = 0; form factor = RMS/average = 1.11; peak factor = peak/RMS = 1.414.

Inductive reactance XL = 2πfL (opposes current, current lags voltage by 90°); capacitive reactance XC = 1/(2πfC) (current leads voltage by 90°).

Impedance Z = √(R² + (XL − XC)²); power factor = cos φ = R/Z; real power P = VI cos φ, reactive power Q = VI sin φ (var), apparent power S = VI (VA).

Three-phase star: VL = √3 × Vph, IL = Iph. Delta: VL = Vph, IL = √3 × Iph. Total three-phase power P = √3 VL IL cos φ.

Energy: 1 kWh = 1000 W × 3600 s = 3.6 × 10⁶ J; a 100 W lamp run 10 h consumes 1 unit (1 kWh).

Copper: resistivity ≈ 1.72 × 10⁻⁸ Ω·m, high conductivity, best jointing and bending; aluminium: ≈ 2.83 × 10⁻⁸ Ω·m, lighter and cheaper but needs larger cross-section and special connectors to avoid bi-metallic corrosion.

Conductor resistance R = ρL/A; doubling length doubles R, doubling area halves R. A 1.5 mm² copper conductor has roughly 12 Ω per 1000 m at 20 °C.

PVC (thermoplastic) insulation: 70 °C normal rating, softens on overload; XLPE/EPR (thermoset): 90 °C rating, better short-circuit and heat withstand. Choose thermoset for hot locations and motor circuits.

Common Indian cable sizes (mm²): 1.0, 1.5, 2.5, 4, 6, 10, 16, 25, 35, 50, 70, 95 - lighting 1.5 mm², 5 A sockets 2.5 mm², power/geyser circuits 4 mm² and above.

Wiring systems: cleat, casing-capping (wood/PVC), conduit (surface, concealed, recessed), batten, CTS/PVC-sheathed, and busbar trunking for heavy industrial loads; concealed conduit is standard in modern buildings.

Conduit rules: conduit diameter ≥ 1.5 × cable bundle diameter; conduit fill ≤ 40 % of internal area; bends limited to two 90° between draw boxes; use PVC conduit in damp/corrosive areas.

Flexible cords are rated by core count and size (e.g., 3 × 1.5 mm²); earth core must be green-yellow and never used as a live or neutral conductor.

Materials for panels: MS sheet 1.6–2 mm for enclosures, powder coating or epoxy paint for corrosion protection, insulating sheet (FRP/bakelite) for mounting live parts, and copper/Al busbars with heat-shrink sleeving.

Stranding improves flexibility: a 2.5 mm² flexible cable uses many fine strands, while a solid conductor suits fixed wiring only; never tin or solder a terminal that relies on screw clamping.

Crimping is preferred to soldering for panel terminations: use the correct lug (ring, fork, pin, bootlace ferrule) matched to conductor and stud size, and verify with a pull test.

Cable lugs: copper lugs for copper conductors, bimetallic lugs where aluminium meets copper; apply anti-oxidant compound on aluminium strands before crimping.

Accessories: switches (one-way, two-way, intermediate), sockets (2-pin, 3-pin 6 A/16 A), ceiling rose, batten holder, angle holder, plug tops, MCB, distribution board, junction box, and modular plates.

Two-way switching uses two two-way switches with a two-wire strapper; intermediate switching adds a four-terminal intermediate switch between them for three or more control points.

Terminal identification: phase/live brown (old red), neutral blue (old black), earth green-yellow (old green); three-phase phases are red, yellow, blue in Indian practice.

Busbars in panels: size by current density (copper ≈ 1.2–1.6 A/mm² for continuous enclosed duty), support on insulators, maintain phase-to-phase and phase-to-earth clearances, and torque all bolted joints to specification.

Ferrule and wire numbering: each core in a control panel gets a unique number matching the schematic; ferrules are fitted before termination and must be legible and permanent.

Domestic circuits: separate lighting and power sub-circuits, one circuit per 800 W (lighting) or 1000–3000 W (power) as per IS 732 practice; each sub-circuit protected at the distribution board.

Load calculation: total connected load × diversity factor gives maximum demand; single-phase domestic supply is 230 V, three-phase industrial supply 415 V, 50 Hz.

Lighting circuit wiring: loop-in system (live, neutral, earth looped through ceiling rose) is preferred over joint-box method because fewer joints are concealed.

Industrial installation: cable trays above 2.5 m, separate power and control cables, earthing conductor run with every feeder, and motor circuits with isolator within sight of the motor.

Cable derating: apply factors for ambient temperature, grouping, and installation method (in air, in conduit in wall, buried); final current rating = tabulated rating × all applicable factors.

Voltage drop limit: keep ≤ 3 % for a final sub-circuit and ≤ 5 % from origin to load; drop = (2 × I × L × ρ)/A for single-phase two-wire circuits.

Testing after installation: insulation resistance (≥ 1 MΩ at 500 V DC for LV circuits), polarity, earth continuity, and RCD/ELCB trip test before energising.

Panel layout practice: incoming → metering → main isolator/MCCB → busbar → outgoing feeders; maintain 1 m working clearance in front, cable entry from bottom, and label every feeder.

Contactors: main contacts carry motor current, auxiliary NO/NC contacts handle control logic; coil voltage commonly 110 V, 230 V or 415 V AC, or 24 V DC.

Overload relay: thermal (bimetallic) or electronic; set to motor full-load current (FLC), class 10 for normal starting, class 20/30 for high-inertia loads.

MCB: thermal-magnetic, curve B (3–5 In, resistive/lighting), C (5–10 In, general), D (10–20 In, motors/high inrush). MCCB: adjustable thermal and magnetic settings for larger feeders.

Symbols per IS/IEC 60617: contactor coil rectangle, NO contact open gap, NC contact closed bar, thermal overload with heater element symbol, fuse rectangle, earth three declining bars.

Push buttons: green = start/NO, red = stop/NC, mushroom red = emergency stop with latching; selector switches for auto/manual, and indicating lamps (red = ON/run, green = OFF, amber = trip/warning).

Timers: ON-delay (starts timing when energised) versus OFF-delay (starts timing when de-energised); star-delta and auto-restart circuits depend on correct timer type.

Panel accessories: terminal blocks, DIN rail, wire ducts, door-mounted isolator handle, CTs and ammeter/voltmeter with selector switch, surge protection device, and anti-condensation heater.

Control transformer steps 415 V down to 230/110 V for control circuits, isolating the operator from line voltage and limiting fault energy.

DOL starter: contactor + overload + start/stop push buttons; simple and cheap, used up to about 5 HP (3.7 kW); starting current 6–8 × FLC.

Star-delta starter: motor starts in star (phase voltage = VL/√3, starting torque and current reduced to one-third), then changes to delta after a set time; needs a six-terminal motor.

Auto-transformer starter: tapping at 50–80 % reduces starting current by the square of the tap; smoother than star-delta and suits large motors.

Soft starter uses thyristor phase control to ramp voltage; VFD (V/f control) varies both frequency and voltage for controlled acceleration and energy saving on variable-torque loads.

Reverse-forward control: two contactors with NC auxiliary contacts interlocked so both cannot energise together; also interlock through push buttons for safety.

No-volt protection: the contactor drops out on supply failure and does not self-restart until START is pressed again - mandatory for motor starters.

Sequence/interlock logic: read the ladder from left (live) to right (neutral); a series element is an AND condition, a parallel element is an OR condition.

Motor protection set points: overload at FLC, single-phasing protection, under/over-voltage relay, and earth-fault relay on higher-rated motors; check direction of rotation before coupling the load.

Fuse: melts on overcurrent, ruptures at the rated breaking capacity; HRC fuses are filled with quartz sand and give fast, current-limiting clearance. Never rewire a blown fuse with thicker wire.

Earthing types: plate earth, pipe earth, rod earth, and strip/loop earth; earth pit resistance should be ≤ 1 Ω for a substation and generally ≤ 5 Ω for domestic installations.

Earthing conductor sizing: for phase conductors up to 16 mm², the earth conductor is the same size; above that, roughly half the phase conductor (with a minimum), per IS 3043 guidance.

ELCB/RCD: current-operated RCD at 30 mA protects people against earth leakage; 100–300 mA for fire/equipment protection. An RCD does not protect against overload or line-to-neutral shock.

Protection coordination: the upstream device must have a higher rating and its time-current curve must lie above the downstream device so only the faulty circuit trips.

Safe isolation procedure: identify, isolate, lock off/tag, prove the tester on a known live source, test dead, and re-prove the tester before touching conductors.

First aid for electric shock: switch off or separate the casualty with dry insulating material, call for help, start CPR if breathing has stopped, and treat burns without removing stuck clothing.

Fire classes and extinguishers: Class C (gases) and electrical fires need CO₂ or dry powder; never use water or foam on live electrical equipment.

Ammeter is connected in series and has very low resistance; voltmeter in parallel with very high resistance; an ammeter with a shunt extends range, a voltmeter with a multiplier (series resistance) extends range.

Moving-coil instruments measure DC and read average value; moving-iron instruments measure AC and DC and read RMS; dynamometer type measures AC/DC power accurately.

Energy meter (kWh): disc revolutions relate to load by E = (revolutions × 3600)/(meter constant × time); a creeping meter with no load indicates a fault.

Megger (insulation resistance tester): apply 500 V DC for LV circuits, 1000 V for LT cables/motors; minimum acceptable IR is 1 MΩ, and ≥ 1 MΩ per kV + 1 MΩ for machines.

Multimeter use: select correct function and range, check leads and fuse, and never measure resistance or continuity on a live circuit.

Continuity and polarity tests: confirm earth continuity from the farthest point back to the earth bar, and confirm that the switch is in the live conductor, not the neutral.

Clamp meter measures current by magnetic field without breaking the circuit; clamp only one conductor at a time, otherwise the fields cancel.

Wheatstone bridge for medium resistance, Kelvin double bridge for very low resistance, and megger/insulation tester for high resistance measurements.

Indian Electricity Rules, 1956 (now superseded by the Electricity Rules, 2005 and the CEA Measures Relating to Safety and Electric Supply Regulations, 2010) govern supply, installation and safety; the CEA Regulations are the current technical reference.

Rule 44 (IE Rules): supply voltage and permissible variation; Rule 61: earthing requirements; Rule 64: use of energy at low/medium voltage; Rule 67: leakage current on consumer premises.

IE Rule 50: installation and maintenance of supply lines; Rule 51: provisions for safety of public; minimum overhead line clearance over roads and buildings is specified in the rules.

IS 732 - Code of Practice for Electrical Wiring Installations (system design, protection, earthing, testing); IS 3043 - Code of Practice for Earthing.

IS 694 - PVC insulated cables up to 1100 V; IS 1554 - PVC insulated power cables; IS 7098 - XLPE cables; IS 2516 - switchgear and controlgear; IS 8828 - MCBs.

IS 12640 / IS 60947 series cover RCCBs and low-voltage switchgear; IS 4691 covers LT distribution boards; IS 13947 covers contactors and motor starters.

Licensing: a licensed electrical contractor and a competent wireman (with appropriate competency certificate) are required for installation work; the supply authority inspects and energises.

Permissible voltage variation: ± 6 % for LV supply; frequency 50 Hz ± 3 % (per CEA regulations).

Estimation sequence: take off quantities from the drawing (points, meters of conduit, cable sizes, accessories), apply wastage (5–10 % on cable and conduit), then multiply by current market rates.

Material cost + labour cost (as % of material or per point) + overheads (10–15 %) + contractor profit (10–15 %) + GST gives the quoted price; always state the rate basis and validity.

Panel costing includes enclosure, busbars, switchgear, contactors, relays, wiring, ferrules, terminal blocks, labels, testing, and painting - list each as a separate line item.

Preventive maintenance schedule: monthly visual check and cleaning, quarterly terminal torque check and IR test, half-yearly contact inspection and relay calibration, annual full panel shutdown servicing.

Thermal imaging detects loose joints and overloaded busbars before failure; contact resistance rises with loose terminals, causing heating and eventual fire.

Contact maintenance: pitted or welded contactor contacts are replaced, not filed; check coil voltage, spring pressure and arc chutes; keep spares for critical starters.

Record keeping: maintenance log with date, equipment, fault, action taken, and IR/contact-resistance readings lets you trend deterioration and justify replacement.

Common panel faults: coil open circuit (no operation), welded contact (motor runs after stop), loose neutral (intermittent control failure), and burnt terminal from under-torqued connection.

Technical reporting: state the job, the measurement or observation, the standard limit, and the action taken - e.g., 'IR of motor 0.4 MΩ against 1 MΩ minimum; motor dried and retested at 5 MΩ.'

Work order and permit-to-work: never start work without a signed permit; record isolation points, lock/tag numbers, and the person authorising the work.

Handover communication: pass on incomplete jobs with the exact state of isolation, temporary connections, and any defeated protections in writing.

Team roles on a panel job: estimator, panel builder/wireman, tester, and commissioning engineer; each signs off their stage in the inspection and test plan.

Interview-ready basics: explain star-delta starting, why the earth conductor is green-yellow, and what an RCD does - these are common trade questions.

Safety communication: toolbox talk before each shift covering hazards, PPE, and emergency contacts; report near-misses, not just accidents.

Customer interaction: explain the fault in plain language, quote before starting chargeable work, and leave a written test certificate with readings.

Digital skills: read single-line diagrams and ladder schematics, use a multimeter/megger correctly, and record readings in a maintenance app or log sheet.