Electrical Fundamentals and Safety
What this domain tests
Electrical Fundamentals and Safety is the foundation domain. The exam checks Ohm's law, power in single-phase AC, series and parallel loads, protective earthing, shock protection and safe work habits in a domestic repair shop.
Core rules
- For a resistive load, V = I × R, P = V × I = I²R = V²/R. Domestic supply is nominally 230 V, 50 Hz; the peak value is about 325 V.
- Domestic appliances are connected in parallel, so each gets 230 V and switching one does not break the others.
- Protection is coordinated: correct cable current-carrying capacity, MCB rating, 30 mA RCCB for socket circuits, and a low-resistance earth electrode.
- Isolate before work, lock/tag the isolator, prove the tester on a known live source, then prove dead. Discharge capacitors and treat neutral as a live conductor until isolated.
- Use insulated tools, rubber-soled footwear and eye protection. For shock, switch off or safely separate the casualty, call emergency help, and give CPR if trained.
Worked example
A 2000 W geyser is wired to 230 V. Current I = P/V = 2000/230 = 8.70 A. Element resistance at operating temperature R = V²/P = 230²/2000 = 26.45 Ω. A 16 A MCB and 2.5 mm² copper conductor are reasonable, provided the installed cable's current-carrying capacity and voltage drop are checked. The metal tank must be bonded to the protective earth, and the circuit should be on an RCCB.
Traps that cost marks
Using 240 V when the question says 230 V; confusing kW with W; assuming the neutral is safe to touch; selecting an MCB larger than the cable can carry; and forgetting that a cold heating element has a lower resistance than its hot value.