Electrical Wiring Questions and Answers viva Interview

What are AC and DC supply?

AC – Alternating current is an electric current that periodically reverses its direction of current flow. One complete cycle of an AC supply consists of a positive half-cycle and a negative half-cycle. The frequency of an AC supply is the total number of complete cycles per second.

DC – Direct Current is an electric current that flows in only one direction. DC supply has a fixed polarity with a positive and negative terminal, the current flows from positive to the negative terminal.

electrical wiring

What is the difference between neutral and earth lines?

Neutral – Return line or return path of current, connected to the start point of the transformer usually connected to ground.

Earth – Connected to earth or soil through an earth rod that offers a low resistance current path for electric discharges. It carries current during a fault condition and not a current-carrying path under normal condition.

Why earthing is required in electrical wiring?

In electrical systems earthing has an important role in protection, it discharges fault current and prevents electric shocks, damage of appliances, etc.

What is an isolator?

An isolator is a mechanical switching device used for isolating a circuit or equipment from the power source.

What is called a main switch?

The main switch is the master switch which isolates all the house electric circuits from the power supply. The output from the energy meter is connected directly to the main switch.

What is MCB?

Miniature Circuit Breaker or MCB is an electromechanical device used to protect an electrical circuit from an overcurrent due to short circuit or overload. When the current through the MCB reaches the rated trip current value it trips and breaks the circuit.

MCB can be reset as a normal switch just flip the knob to ON.

Difference between MCB and FUSE? Which one is preferable?

Both devices have the same function they are used to protect the electrical system from over current and overload, but they are different in both construction and operation.

MCB’s are more preferable because it offers better sensitivity, accuracy, precision, etc. The main advantages are MCBs can be operated safely as just like a switch. Whereas a fuse needs to very carefully plugin to and out from live conductors and the fuse wires need to be replaced after every burnout.

What is ELCB?

An Earth Leakage Circuit Breaker is a safety device which protects the circuit from earth leakage, an ELCB detects if any voltage is present in the body parts of appliances or any leakage current in the earth line.

What is RCCB?

A Residual Current Circuit breaker is a circuit breaker that interrupts the current flow when an earth fault is detected. It operates if there is any considerable change in the current value through the phase and neutral lines. Common RCCB used in house wiring trips for an unbalance of above 30 mA.

ELCB or RCCB which is better to use in wiring? Why?

Both ELCB and RCCB detect and protect from earth fault and they are often referred or considered as same. But an ELCB works only when an earth faults cause the leakage of current through the earth line. That is the leakage current must go through the earth line.

Whereas an RCCB operates when any imbalance is detected in the ampere of current through the phase and neutral lines. For any type of earth fault, there will be a difference in the value of incoming current through the phase and the return current through the neutral line.

So, the RCCB offers better protection than ELCB by operating for any type of earth fault irrespective of the path of leakage current.

Refer : MCB vs ELCB vs RCCB

How to wire one lamp controlled by two switches?

By wiring, the load using multiway switching or staircase wiring one lamp can be controlled from two switches placed at different locations like the top and bottom of a staircase, indoor and outdoor of the home, etc.

List a few Common types of Switches in electrical wiring?

  • Single Pole Single Throw
  • Single Pole Double Throw
  • Double Pole Single Throw
  • Intermediate switch

Refer more,

8 Responses

  1. mr s j davies says:

    hello i have purchased a gammont wall lamp and it only has the live and neutral wires in the block but no earth wire please can you tell me why there is there no earth wire and can it be installed safetly without one thank you

    • Govind says:

      If the external surface of the wall lamp is metallic or conductive then it has a possibility of leakage only if the insulation of conductors fails. As long as the lamp circuit has proper insulation it is safe.
      Usually, lamps might not have an earth connection as the chance of human contact to wall lamps are less and the possibility to cause any leakage is less.
      Make sure your wires are good and all contacts are well insulated. If the body of your lamp is nonconductive then the chance of shock or leakage is very less. If you doubt the safety, then an earth wire can be connected to the metal casing of the lamp.

  2. Frank Hopfinger says:

    I have a four-way switch that I want to install a receptacle below the switch. There is a black, white and red wire on the switch. Is there a way to get a hotline for the receptacle to be installed?

    • Dave says:

      Usually the RED wire is used for phase line, so most probably red will have the hotline. You can use a tester to find the phase line.

  3. Phindile says:

    What do the regulations stipulate regarding the earthing of flexible conduit?

  4. JEMAL ADEM says:


  5. John kimani says:

    I like it

  6. Jeff says:

    I have a trailer at a campgrounds where I use the 50AMP receptacle plug for my unit which has it’s own breaker.
    The power stand also has another 30AMP receptacle with a separate breaker that’s not being used.

    I would like to use the 30AMP receptacle to power to my refrigerator and 5 more outlets on my deck.
    I have a 30AMP, 3 wire extension cord (2 hots and a neutral) I’d like to run to a 2 breaker sub panel using 1 leg and a 15AMP breaker.
    I can not open the campgrounds power stand box so running a 4th wire for ground is out.

    What would be the best way to go about this so I have a little more protection then just running a 2 wire extension cord?

    If groundrods are needed do I bond the neutral?

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