Professional Knowledge (Civil / Electrical Engineering)
Professional Knowledge: Civil and Electrical Engineering
The professional knowledge paper is branch-specific: JE (Civil) candidates answer civil engineering questions; JE (Electrical) candidates answer electrical engineering questions. It tests code-based design, mechanics, materials, estimation, and-for electrical-circuits, machines, power systems and installation practice.
Civil core
- IS 456 limit-state design: compare factored demand (1.5 DL + 1.5 LL, etc.) with factored capacity; check deflection, crack width and durability (minimum cement content, maximum w/c ratio).
- Beam formulae: simply supported, UDL w over span L: Mmax = wL²/8, Vmax = wL/2; central point load W: Mmax = WL/4. Cantilever UDL: Mmax = wL²/2 at fixed end.
- Surveying/estimation: reduce levels by height of instrument or rise-and-fall; centre-line method for walls; long wall/short wall for masonry.
Electrical core
- DC: KCL at nodes, KVL around loops; Thevenin equivalent for load-current problems.
- AC: P = VI cosφ, Q = VI sinφ, S = VI; capacitor bank Qc = P(tanφ1 − tanφ2) for power-factor correction.
- Transformer emf: E = 4.44 f N Φm; losses split into iron (constant) and copper (I²R, load-dependent).
- Earthing and protection: earth resistance matters for touch/step voltage; protective device ratings coordinate with cable ampacity.
Worked example
A 10 kW load runs at 0.8 lagging power factor. Find the capacitor rating to raise pf to 0.95. tanφ1 = tan(cos⁻¹0.8) = 0.75; tanφ2 = tan(cos⁻¹0.95) = 0.329. Qc = 10(0.75 − 0.329) = 4.21 kVAr. Reasoning: real power stays 10 kW; reducing reactive demand reduces line current and losses.
Traps
Using working stress formulae in a limit-state question; forgetting load factors; mixing kW/kVA; applying single-phase formulae to three-phase; ignoring diversity in cable sizing.