ITI Electrician Interview Questions and Answers

What is Ohm's law?

At a constant temperature, the current through a conductor is directly proportional to the voltage across it: V = I × R. For example, a 230 V supply across a 46 Ω heating element draws 5 A.

How to say it: Give the formula and one worked number. It shows you can use it.

What is the difference between AC and DC?

DC flows in one direction with fixed polarity, as from a battery. AC reverses direction many times a second. Indian mains supply is AC at 50 Hz: 230 V between phase and neutral, and about 400 to 415 V between two phases of a three-phase supply.

What are phase, neutral and earth?

Phase carries the supply voltage. Neutral is the return path and stays close to earth potential because it is earthed at the transformer. Earth is a protective conductor connected to an earth electrode; it carries current only during a fault, so that the fuse or breaker operates and metal bodies do not stay live.

How to say it: The phrase "earth carries current only during a fault" is the part interviewers listen for.

Why is earthing done, and which types do you know?

To give fault current a low-resistance path to ground so the protective device trips quickly, and to keep the metal body of equipment at earth potential so a person touching it is not shocked. Pipe earthing and plate earthing are the two types taught in ITI.

What is the difference between a fuse, an MCB and an RCCB?

A fuse melts on overcurrent and has to be replaced. An MCB trips on overload and short circuit and can be switched on again. An RCCB (often still called an ELCB) trips when the current going out on phase and returning on neutral differ. That is, current is leaking to earth. A 30 mA RCCB is used to protect people. An RCCB alone does not protect against overload; an RCBO does both.

How to say it: If you explain the RCCB as "phase and neutral current do not match", you have answered better than most candidates.

What is the difference between star and delta connection?

In star, one end of each of the three windings is joined at a common point; line voltage is √3 times phase voltage and line current equals phase current. In delta, the windings are joined end to end in a closed loop; line voltage equals phase voltage and line current is √3 times phase current.

Why is a star-delta starter used for a motor?

A three-phase induction motor started direct on line takes several times its full-load current. Starting in star puts 1/√3 of the line voltage on each winding, which cuts the starting current and torque to about one-third. When the motor has picked up speed, the starter changes over to delta for normal running.

How to say it: Draw the changeover if you are given paper. It shows you have wired one.

How do you reverse the direction of a three-phase motor?

Interchange any two of the three supply phases at the motor terminals. For a single-phase capacitor motor, reverse the connections of the starting (auxiliary) winding.

What does the capacitor in a ceiling fan do?

It shifts the phase of the current in the starting winding so that the single-phase motor produces a rotating field and can start by itself. A weak capacitor gives a fan that hums, starts only when pushed, or runs slowly.

What is the difference between a contactor and a relay?

Both are electrically operated switches. A contactor is built to switch heavy load current, such as a motor's, through its main contacts, and has auxiliary contacts for control. A relay switches small control currents. A contactor with an overload relay makes a DOL starter.

How do you check whether a circuit is dead?

With a voltage tester rated for the supply: first prove the tester on a known live source, then test the circuit, then prove the tester again. Only then start work.

How to say it: Call it "prove (test) prove". It is a standard safe-isolation step.

What is a megger used for?

To measure insulation resistance. For 230/415 V wiring a 500 V insulation tester is commonly used. With the supply off and the loads disconnected, you test between conductors and between each conductor and earth. A high reading in megohms is good; a low reading points to damaged insulation or moisture.

How do you check continuity with a multimeter?

Switch off and isolate the circuit, set the meter to continuity or the lowest resistance range, and touch the probes to the two ends. A beep or a reading close to zero means the conductor is continuous. Never measure resistance on a live circuit.

What is a clamp meter (tong tester) used for?

To measure the current in a conductor without breaking the circuit. Clamp it around one conductor only: around both phase and neutral together it reads close to zero, because their magnetic fields cancel.

How to say it: The "one conductor only" point is the detail that shows practical use.

Which tools are in your kit?

Combination plier, side cutter, wire stripper, insulated screwdrivers, line tester, electrician's knife, hammer, poker, measuring tape, and a multimeter. Name each with one use.

How to say it: Interviewers sometimes hand you a tool and ask what it is for: be ready.

What do you do before working on a circuit?

Switch off and isolate at the distribution board, lock and tag the isolator (lock-out tag-out), test for dead with a proven tester, then work with insulated tools. Never assume someone else has switched it off.

Someone is getting an electric shock. What will you do?

Do not touch the person directly. Switch off the supply at once; if you cannot, separate the person from the conductor with dry, non-conducting material such as a wooden stick. Call for medical help, and if the person is not breathing, give CPR only if you are trained.

How to say it: Start with "I will not touch the person". That is the first thing they want to hear.

Which extinguisher is used on an electrical fire?

CO2 or dry chemical powder. Never water or foam on live equipment. Switch off the supply first if it is safe to do so.

Explain staircase wiring.

One lamp controlled from two places using two two-way switches. Phase goes to the common terminal of the first switch; its two other terminals connect to the two matching terminals of the second switch; the common of the second switch feeds the lamp; neutral goes straight to the lamp.

How to say it: Draw it before you wire it: supervisors like to see the diagram first.

What wiring jobs come up in the practical test?

Commonly: staircase wiring, a board with a lamp, fan with regulator and socket, a tube-light circuit, a DOL or star-delta starter connection, or finding a fault in a given circuit. Practise drawing each circuit and wiring it neatly, with every joint tight and every screw terminal clean.

How to say it: Neat routing and tight terminations are marked, not only whether the lamp lights.

A motor trips on overload as soon as it starts. Where will you look?

Check all three phases are present (single phasing), the overload relay setting against the motor's full-load current on its nameplate, the load on the motor or a jammed bearing, and the winding insulation with a megger. Fix the cause before resetting again.