Question

The following question is a source-based/case-based question that follows. Read the case carefully and answer the questions that follow.

In our homes, we receive the supply of electric power through a main supply also called mains, either supported through overhead electric poles or by underground cables. In our country the potential difference between the two wires (live wire and neutral wire) of this supply is 220 V.

1. Write the colours of the insulation covers of the line wires through which supply comes to our homes.  (1)
2. What should be the current rating of the electric circuit (220 V) so that an electric iron of 1 kW power rating can be operated?  (1)
3. 1. What is the function of the earth wire? State the advantage of the earth wire in domestic electric appliances such as electric iron.  (2)
      OR
   2. List two precautions to be taken to avoid electrical accidents. State how these precautions prevent possible damage to the circuit/appliance.  (2)

Answer 1

i. Colours of the Insulation Covers:

• Live (Line) Wire: Red (in older standards) or Brown (in updated IEC standards)
• Neutral Wire: Black (older standards) or Blue (in updated IEC standards)

ii. Current Rating of the Circuit:

An electric iron rated at 1 kW (1000 W) operating on 220 V draws a current given by

`I = P/V = (1000W)/(220 V) ≈ 4.55 A`

Thus, the circuit should be rated at approximately 5 A to safely operate the iron.

iii. a. 

• Function: There is a low-resistance path to the ground for any leakage or fault current through the earth line.
• Advantages: When a live part of a device, like an electric iron, touches the metal case by mistake, the earth wire safely sends the fault current to the ground. This helps keep the case from going live, which lowers the user's risk of getting an electric shock.

OR

b. Precautions to Avoid Electrical Accidents:

• Ensure Proper Insulation: 
  • Precaution: Make sure to check and fix the insulation of your appliances and lines on a regular basis.
  • Benefit: It keeps live wires from being accidentally touched and lowers the risk of short circuits and electric shocks.
• Use of Protective Devices:
  • Precaution: In home circuits, put in fuses, circuit breakers, or earth leakage circuit breakers (ELCBs).
  • Benefit: These gadgets cut the circuit off immediately if there is an overload or a problem. This keeps appliances from getting damaged and lowers the risk of fire and electrocution.