RRB ALP Wireman Trade — Complete CBT-2 Study Guide

• Domestic wiring systems: Casing-capping (older method, wires enclosed in PVC casing fixed to walls), Batten wiring (cables clipped along a wooden/PVC batten), Concealed conduit wiring (conduit embedded in walls before plastering — the standard for modern residential construction, giving a clean finish and good mechanical protection). • Industrial wiring typically uses heavier-gauge conductors, conduit or cable tray systems (open metal trays for organizing multiple cables), and must account for higher loads, three-phase supply, and more stringent protection/isolation requirements than domestic wiring. • Wiring accessories: Switches (control circuit ON/OFF, always connected in the PHASE/live wire, never the neutral, so the load is fully de-energized when off), Sockets/outlets, Distribution board (houses circuit breakers/fuses, splits the incoming supply into multiple individually-protected circuits). • Cable sizing must account for the connected load's current rating with an adequate safety margin — an undersized cable overheats under load, posing a fire risk; correct sizing follows standard current-carrying capacity tables for the cable type/installation method.

• A cable joint electrically and mechanically connects two cable ends (or a cable to a terminal) — a poor joint has higher resistance, causing localized heating that can eventually lead to joint failure or fire. • Common jointing methods: Twisted joint (simple, low-current applications only), Soldered joint (twisted first, then soldered for a stronger, lower-resistance permanent connection), Crimped joint (using a crimping tool and connector/lug, widely used in modern practice for its speed, consistency, and reliability without heat). • Insulation of a joint (using insulation tape, heat-shrink tubing, or a proper junction box) must restore insulation at least equal to the original cable insulation rating — an inadequately insulated joint is both a shock and short-circuit hazard. • Termination lugs/ferrules are used to terminate stranded conductors into terminal blocks/equipment — ensures all strands make good contact and prevents stray strands from causing short circuits.

• Purpose of earthing: provides a low-resistance path for fault current, ensuring protective devices (fuse/MCB) trip quickly during a fault, and limits the touch voltage on an equipment's metal body to a safe level, preventing electric shock. • Plate earthing uses a buried metal (GI or copper) plate connected via an earth wire — commonly used for larger installations requiring lower earth resistance. • Pipe earthing uses a galvanized iron pipe driven vertically into the ground — simpler and more common for smaller/domestic installations. • Earth resistance testing (using an earth tester/megger) verifies the earth electrode's resistance is within acceptable limits (as low as practical, per applicable electrical safety codes) — earthing effectiveness should be checked periodically, since soil conditions (moisture, corrosion) can degrade it over time.

• Electric shock severity depends on current magnitude through the body, path (hand-to-hand or hand-to-foot, the latter through the heart is more dangerous), and duration of contact — even relatively small currents (as low as ~10-20mA AC) can cause muscle paralysis preventing the person from letting go. • Personal protective equipment for electrical work: insulated gloves, insulated tools, safety footwear (with non-conductive soles) — rated for the voltage level being worked on. • Lockout-Tagout (LOTO) procedure isolates and locks out equipment from its power source before maintenance, with a tag identifying who performed the lockout — prevents accidental re-energization while someone is working on the equipment. • MCB (Miniature Circuit Breaker) protects against overload and short-circuit; ELCB/RCCB protects against earth leakage current (shock protection) — a complete, safe installation typically uses both types of protection together, not either alone.