Basic Electrical Fundamentals and Safety
What the exam tests
This domain checks whether you can apply Ohm's law and power relationships to real 230 V/415 V, 50 Hz circuits and whether you can state and justify the safety rules that govern work on them. Expect numerical questions plus direct safety questions.
Core rules
- Ohm's law: V = IR. Power: P = VI = I²R = V²/R. For AC, P = VI cos φ single phase and √3 V_L I_L cos φ three phase.
- Maharashtra supply values: 230 V phase-to-neutral, 415 V phase-to-phase, 50 Hz.
- Current through the body above roughly 30 mA can be lethal; a 30 mA RCCB is used for personnel protection, but it does not replace earthing or overload protection.
- Prove dead, lock out, tag out and test before touching. IE Rules 1956 and IS 732 are the governing references for installation and safety.
Worked example
A 230 V, 2 kW water heater runs for 3 hours. Find current, resistance and energy. I = P/V = 2000/230 = 8.70 A. R = V²/P = 230²/2000 = 26.45 Ω. Energy = 2 kW × 3 h = 6 kWh. The 8.70 A load needs a circuit and MCB rated above it, with cable derated for enclosure and ambient temperature.
Traps
Using 415 V as the phase voltage, mixing kW and kVA without power factor, and assuming an RCCB removes the need for a good earth. An RCCB also does not protect against line-to-line contact.