ITI Electrician Viva Questions and Answers

What test do you do before switching on a new wiring?

Continuity test (correct connections, no open circuit), polarity test (switch in the phase wire), and insulation resistance test with a megger between conductors and between conductors and earth.

How to say it: Say all three tests in this order.

Why is the switch always connected in the phase wire?

So that when the switch is off, the lamp or appliance is completely disconnected from the live supply and is safe to touch or repair.

What wire size is used for lighting and for power sockets in house wiring?

Commonly 1.5 sq mm copper for lighting circuits and 2.5 sq mm for 6 A / 16 A power socket circuits (4 sq mm for heavier loads like an AC), as per the load and the wiring rules.

What is the difference between an MCB and a fuse?

Both protect against overcurrent. A fuse melts and must be replaced; an MCB trips and can be reset. An RCCB (or ELCB) protects against earth leakage current, which saves people from shock.

What is two-way wiring (staircase wiring)?

One lamp controlled from two places using two two-way switches, so the light can be switched on at the bottom of the stairs and off at the top.

Why is earthing done?

To give fault current a low-resistance path to earth, so the protective device trips and the metal body of an appliance does not stay live. It protects people and equipment.

What are the types of earthing?

Pipe earthing and plate earthing are the common ones; strip or rod earthing is also used. Salt and charcoal around the electrode keep the soil moist and the resistance low.

What does a megger measure?

Insulation resistance, in megohms. A low reading means the insulation is damaged or damp.

How is an ammeter connected, and how is a voltmeter connected?

Ammeter in series with the load; voltmeter in parallel (across) the load.

What does a multimeter measure?

Voltage (AC and DC), current, resistance and continuity; many also test diodes and capacitance.

State Ohm's law.

At constant temperature, current through a conductor is directly proportional to the voltage across it: V = I × R.

What is the total resistance of resistors in series and in parallel?

Series: R = R1 + R2 + …. Parallel: 1/R = 1/R1 + 1/R2 + …. The parallel total is always less than the smallest resistor.

Why is a starter used with a three-phase induction motor?

At start, the motor draws a very high current. A starter (DOL for small motors, star-delta or soft starter for bigger ones) limits the starting current and gives overload and no-volt protection.

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

Interchange any two of the three supply phases.

What is the working principle of a transformer?

Mutual induction: an alternating current in the primary winding produces a changing flux that induces a voltage in the secondary winding. It works only on AC.

What is the frequency of the supply in India?

50 Hz. Single-phase domestic supply is 230 V; three-phase line voltage is 415 V (400 V nominal).

What safety steps do you take before working on a circuit?

Switch off and isolate the supply, remove the fuse or lock the MCB, put a caution tag, test that the circuit is dead with a tester, and use insulated tools.

What do you do if someone gets an electric shock?

Switch off the supply or separate the person using a dry insulating object, then give first aid (check breathing, CPR if needed) and call for help.