Odisha CHSE +2 VOC-ITV Wireman Control Panel common mistakes
Odisha CHSE +2 VOC-ITV Wireman Control Panel · Understand the traps and how to avoid them.
Using the formula P = VI directly for a single-phase inductive load without multiplying by the power factor, so a 230 V, 10 A motor at 0.8 pf is calculated as 2300 W instead of 1840 W.
Candidates memorise P = VI from basic DC examples and carry it into AC problems, forgetting that only the resistive part of the current does real work; kVA and kW get treated as interchangeable.
What to do instead
Before any AC numerical, write down the given quantities and label each as kW, kVA, or kVAR. State the triangle relationship S = VI, P = VI cos φ, Q = VI sin φ, and always check whether the question gives pf or asks for it. Practise ten mixed single-phase and three-phase problems where the answer must be reported in the correct unit.
Selecting cable or fuse ratings by rough guess rather than by current-carrying capacity, so a 1.5 sq mm copper conductor is chosen for a 20 A water-pump circuit or a 6 A fuse is fitted to a 2 HP motor circuit.
Candidates learn current ratings as isolated numbers without linking them to derating factors, ambient temperature, grouping, and the inrush current of inductive loads, so the first number that 'looks big enough' is used.
What to do instead
Build a one-page reference table of standard conductor sizes (1.0, 1.5, 2.5, 4, 6, 10 sq mm) with their typical current ratings, and apply derating for temperature and conduit grouping. For motors, size the protective device for starting current and the cable for full-load current plus a margin. Work through three complete feeder-sizing exercises end to end.
Drawing control panel schematics with the wrong symbol or with the coil and contact of a contactor shown as the same element, for example using one rectangle for both the operating coil and the power contacts, or omitting the normally-closed auxiliary contact that performs the interlock.
Symbols are memorised visually but not mapped to the physical device, so candidates do not realise that a contactor appears in several places on a drawing, each with a different symbol and a cross-reference.
What to do instead
Redraw a standard DOL starter circuit from memory five times, labelling every element: supply, MCCB, contactor coil, main contacts, NO holding contact, NC stop, NO start, overload relay NC contact, and motor. For each symbol, write the physical terminal it corresponds to. Use cross-referencing (e.g. K1 coil at line 4, K1 contacts at line 2) so the multi-part nature becomes automatic.
Explaining a star-delta starter as if the motor starts in delta and runs in star, or failing to state that the star connection reduces the voltage across each winding to 1/√3 of line voltage and the starting torque to one-third.
The names are counter-intuitive and candidates confuse the starting state with the running state; the voltage and torque relationships are memorised as phrases without derivation.
What to do instead
Write the sequence explicitly: start in star (phase voltage = line/√3, starting current and torque both one-third), then change over to delta for run. Derive the one-third result once from V²/R proportionality, and practise drawing the six-terminal motor connection for both states, including the changeover contactor arrangement and the timer setting.
Treating earthing as a single topic and mixing up the purposes of body earthing, equipment earthing, and system neutral earthing, or quoting an earth resistance value without saying what it is for.
Textbook definitions are learnt as separate facts, so candidates cannot connect earth resistance to the operation of a fuse or ELCB, and they confuse the resistance limit for a substation with that for a domestic installation.
What to do instead
Make a comparison table with columns for purpose, typical resistance limit, conductor size, and the protective device it supports, covering domestic equipment earthing, substation earthing, and lightning protection. For each row, write one sentence explaining what happens if the resistance is too high. Link earth loop impedance to the time in which a fuse must clear the fault.
Reading a megger result incorrectly, such as recording insulation resistance without stating the test voltage or the duration, or accepting a reading taken on a live circuit because the test button was pressed anyway.
Instruments are learnt as procedures rather than as measurements with conditions; candidates do not appreciate that insulation resistance is voltage- and time-dependent and that a live test is both invalid and dangerous.
What to do instead
Before every insulation test, state the checklist: circuit isolated, proved dead, discharge capacitive loads, test voltage selected per equipment rating, reading taken after a defined interval, and the result compared with the minimum acceptable value. Record the reading with units, test voltage, and temperature. Practise writing a short test report for a panel with five circuits.
Quoting Indian Electricity Rules or IS/IEC standards by vague reference ('as per rules, earthing is required') without the specific rule number, the value, or the condition under which it applies, such as the height of an overhead line or the minimum clearance from a building.
Candidates skim the rules because the numbers look arbitrary and are rarely used in workshop practice, so they remember the principle but not the enforceable figure.
What to do instead
Keep a one-page 'numbers sheet' of the values that are actually examined: clearances, earthing resistance limits, conductor sizes for earthing, inspection intervals, and the rule or standard each comes from. Test yourself by covering the numbers and recalling them with their source. When answering, always give the figure and the clause together.
Producing an estimate that lists material cost only, omitting labour, wastage, tools and consumables, overheads, and GST, so a panel that costs ₹8,000 in material is quoted at ₹8,000 instead of a realistic tender figure.
Candidates equate estimation with a shopping list because that is how classroom exercises are framed; the commercial structure of a real quotation is never practised.
What to do instead
Use a fixed estimate template with separate rows for material, wastage percentage, labour (by man-hours at a stated rate), consumables, overheads, profit, and tax. Prepare one complete estimate for a DOL starter panel and one for a distribution board, then compare the two to see how the proportions shift. Always state the basis of each rate.
Answering a maintenance question with a list of checks in no order, instead of a planned sequence such as isolate, prove dead, lock off, inspect, clean, tighten, test, and re-energise, and omitting the record-keeping step.
Preventive maintenance is studied as a set of items rather than a procedure with safety dependencies, so the isolation step gets buried in the middle of the list or left out entirely.
What to do instead
Memorise one canonical maintenance sequence and apply it to every equipment type, adding the equipment-specific checks inside the sequence. For each step, state what could go wrong if it is skipped. Practise writing a maintenance schedule for a motor control centre with frequencies (daily, monthly, annual) and the record to be kept.
Writing workplace communication answers in vague generalities, such as 'I will inform the supervisor politely', instead of giving the actual message, the channel, and the record, when asked how to report a near-miss, request material, or hand over a shift.
Employability skills are treated as soft filler and not revised, so candidates have no concrete format to fall back on and default to polite-sounding sentences with no content.
What to do instead
Learn three fixed formats: a shift handover note (equipment status, work done, pending work, hazards), a material requisition (item, specification, quantity, purpose, date), and an incident or near-miss report (what, where, when, who, immediate action, suggested prevention). Write each one for a realistic panel-workshop scenario and keep them under a page.