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NECO June/July 2025 Free Electrical Installation (Objective and Theory) Questions and Answers Room is now open. Practice with real exam-style content, improve your performance, and pass with ease — 100% free.
Are you preparing for the 2025 NECO Electrical Installation exam? This guide covers both the Objective (OBJ) and Essay sections with complete, NECO-style questions and accurate answers. Designed to help students in technical schools and colleges, this study resource is your best shot at success.
NECO Electrical Installation Objective (OBJ) Questions and Answers 2025
- What is the main function of a fuse in a circuit?
Answer: Protect against overload - Which wire color is used for neutral in a single-phase system?
Answer: Blue - The device used to open and close a circuit manually or automatically is called:
Answer: Contactor - What is the standard unit of electrical resistance?
Answer: Ohm - Which cable is most suitable for use in areas exposed to oil and petrol?
Answer: HOFR cable - A ring circuit is usually protected by a:
Answer: 32A fuse - Which of the following is a part of a contactor?
Answer: Coil - A copper wire of resistance 1 ohm is used in a 240V system. What is the current?
Answer: 240A - What does an MCB protect against?
Answer: Overcurrent and short circuit - What color is used for earth wire in domestic wiring?
Answer: Green/Yellow
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NECO Electrical Installation Essay Questions and Answers 2025
Question 1
(a) Parts of a contactor: Coil, Main contacts, Auxiliary contacts, Armature, Return spring, Enclosure
(b) Five materials on low-tension poles: Lightning arrester, Stay wire, Pin insulator, Fuse cut-out, Transformer
(c) Type of insulator used at HT pole: Disc insulator
(d) Four sizes of bare aluminum conductor: 50 mm², 100 mm², 150 mm², 200 mm²
Question 2
(a) Procedure for earthing in an installation: Insert earth rod in moist soil, connect main earthing conductor, bond exposed metal parts, link to earth bar, test resistance
(b) Best material for earth rod: Copper
(c) Six equipment to be earthed: Electric cooker, Water heater, Metal conduit, Air conditioner, Washing machine, Electric iron
(d) Socket sketch (describe in exam): Terminals include Live (L), Neutral (N), and Earth (E)
Question 3
(a)(i) Current in a 6kW cooker at 240V:
I = 6000 / 240 = 25A
(ii) Resistance of copper wire (L=100m, D=1.5mm):
Area A = πd²/4 = 1.767 × 10-6 m²
ρ = 17.3 × 10-9 Ωm
R = ρL/A = (17.3 × 10-9 × 100) / 1.767 × 10-6 ≈ 0.979 Ω
(b) Resistance of three 5Ω resistors in parallel:
1/R = 1/5 + 1/5 + 1/5 = 3/5 → R = 1.67 Ω
(c) Cable for oil/grease environment: HOFR cable or PVC sheathed armored cable
Question 4
(a) Fused spur box: Contains fuse, Live, Neutral, Earth terminals (draw in exam)
(b) Five IEE ring circuit regulations:
- Cable size must be 2.5 mm² minimum
- Use 30A or 32A fuse/MCB
- Proper earthing must be done
- Should not exceed 100m² floor area
- Test continuity and polarity after installation
Question 5
(a)(i) National Grid: Network for transmitting electricity across the country
(ii) Types of LT poles: Wooden, Concrete, Steel
(b) Voltages in the Nigerian National Grid: 11 kV and 33 kV
(c) Types of power station: Hydro, Thermal, Solar, Wind, Nuclear, Diesel
(d) Distance between HT poles outside towns: 80 to 100 meters
Exam Preparation Tips
- Understand electrical safety rules and IEE regulations
- Practice drawing and labeling electrical components
- Memorize core formulas like Ohm’s Law, Power, and Resistance
- Take time-bound mock exams
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