Most asked Electrical Interview Questions

Basic Electrical Engineering Interview Questions

1. What is Ohm’s Law?

Ohm’s Law states that the current (I) flowing through a conductor between two points is directly proportional to the voltage (V) across the two points and inversely proportional to the resistance (R).

Formula: V = I × R

Applications:

Designing electrical circuits.
Calculating resistance, current, or voltage in systems.

2. Explain the Difference Between AC and DC Current.

Feature	AC Current	DC Current
Direction	Alternates periodically	Flows in one direction
Source	Generators	Batteries
Applications	Power distribution	Electronic devices

3. Why is Earthing Important in Electrical Systems?

Purpose of Earthing:

Provides a safe path for fault currents.
Protects users from electric shocks.
Prevents equipment damage during electrical surges.

Types of Earthing:

Plate Earthing: Uses a metal plate buried in the ground.
Rod Earthing: Uses a rod to dissipate fault currents.

4. What is a Transformer? Explain its Types.

A transformer is a device that transfers electrical energy between circuits through electromagnetic induction.

Functions:

Voltage step-up or step-down.
Isolation for safety.
Power distribution.

Types:

Step-up Transformer: Increases voltage.
Step-down Transformer: Decreases voltage.
Isolation Transformer: Provides electrical isolation.

5. What is Power Factor? Why is it Important?

Power Factor (PF) is the ratio of real power (kW) to apparent power (kVA).

Formula: PF = Real Power / Apparent Power

Importance:

Reduces energy losses.
Improves system efficiency.
Avoids penalties from utility providers for low PF.

6. What is a Circuit Breaker?

A circuit breaker is a protective device that automatically interrupts current flow during overloads or faults.

Working Principle: Operates using electromagnetic or thermal mechanisms to disconnect the circuit.

Types:

MCB (Miniature Circuit Breaker): For small circuits.
MCCB (Molded Case Circuit Breaker): For higher currents.
RCCB (Residual Current Circuit Breaker): Detects leakage currents.

7. What is the Difference Between a Fuse and a Circuit Breaker?

Feature	Fuse	Circuit Breaker
Function	Melts to interrupt	Switches off to break
Reusability	Not reusable	Reusable
Response Time	Faster	Slower
Applications	Low-cost circuits	High-cost systems

8. Describe Three-Phase Power Systems.

A three-phase system provides a consistent and balanced power supply. It’s preferred for industrial use.

Advantages:

Higher efficiency for heavy loads.
Reduced fluctuations.
Lighter and smaller equipment.

Technical Interview Questions for Electrical Engineers

9. What is an Induction Motor? How Does it Work?

An induction motor is an AC motor where the current is induced in the rotor by the magnetic field of the stator.

Applications: Fans, pumps, conveyor belts, and industrial machines.

10. What Safety Measures Do You Follow When Working with Electricity?

Use insulated tools.
Wear appropriate personal protective equipment (PPE).
Ensure circuits are de-energized before working on them.
Follow lockout-tagout (LOTO) procedures.

11. Explain the Working Principle of a Synchronous Generator.

A synchronous generator operates on the principle of electromagnetic induction, where the rotor is mechanically rotated to produce a magnetic field, inducing an alternating voltage in the stator windings.

Applications: Power plants, industrial generators.

12. What is the Difference Between a Relay and a Contactor?

Feature	Relay	Contactor
Application	Low-power circuits	High-power circuits
Size	Smaller	Larger
Arc Suppression	Not designed for arc suppression	Designed for arc suppression

13. What is the Purpose of a Capacitor in AC Circuits?

Capacitors in AC circuits are used to:

Improve power factor.
Filter signals.
Store and release energy.

14. Explain the Concept of Harmonics in Electrical Systems.

Harmonics are voltage or current waveforms at multiples of the fundamental frequency, caused by non-linear loads. They can lead to:

Overheating of equipment.
Misoperation of protective devices.
Reduced efficiency.

15. What is the Role of a PLC in Industrial Automation?

A Programmable Logic Controller (PLC) is used to automate industrial processes by:

Monitoring inputs.
Making decisions based on programmed logic.
Controlling outputs to automate machinery.

16. How Do You Select the Rating of a Circuit Breaker?

Selection is based on:

Load current.
Short-circuit current.
System voltage.
Breaking capacity.

Electrical Apprenticeship Interview Questions

17. Why Do You Want to Pursue an Electrical Apprenticeship?

Sample Answer:

“I want to gain hands-on experience in real-world electrical installations, which will complement my theoretical knowledge. Apprenticeships offer the opportunity to learn under skilled professionals, making me industry-ready.”

18. How Do You Test for Live Circuits?

To test for live circuits:

Use a multimeter, voltage tester, or test lamp to verify voltage presence.
Always ensure the tools are properly calibrated.

Advanced Electrical Engineering Technical Interview Questions

19. What is the Difference Between Star and Delta Connections?

Feature	Star Connection	Delta Connection
Configuration	Three phases connected to a common neutral point	Phases connected in a loop
Voltage	Phase voltage = Line voltage / √3	Phase voltage = Line voltage
Applications	Long-distance transmission	Short-distance, high-power applications

20. Explain the Working of a UPS System.

An Uninterruptible Power Supply (UPS) provides backup power during mains failure. It consists of:

Rectifier: Converts AC to DC.
Battery: Stores energy.
Inverter: Converts DC back to AC for the load.