UK Plug and Fuses [Sample Lesson]

Answer:

(Since I cannot draw, I will describe the standard diagram)

A UK 3-pin plug, when viewed from the back (where the wires are connected), has three terminals.

• Top (longest) pin: Connected to the Earth wire (Green and Yellow stripes).
• Bottom Right pin: Connected to the Live wire (Brown).
• Bottom Left pin: Connected to the Neutral wire (Blue).

The fuse should be located on the Live wire side, within the plug.

       (Earth - Green/Yellow)
             |
             |
             O  (Longest pin at top)
            / \
           /   \
          /     \
         O-------O
     (Neutral - Blue) (Live - Brown, with Fuse)
            

(Diagram represents view from the back of the plug, with cable entry at the bottom)

Answer:

• Live wire: Brown
• Neutral wire: Blue
• Earth wire: Green and Yellow stripes

Answer:

The Live wire carries the alternating potential difference (voltage) from the mains supply (e.g., 230 V in the UK). It is the wire that supplies the electrical energy to the appliance.

Answer:

The Neutral wire completes the circuit by carrying the current away from the appliance back to the mains supply. It is usually at or close to zero potential difference (earth potential).

Answer:

The Earth wire is a safety wire designed to protect the user from electric shock. It is connected to the metal casing of an appliance. If the Live wire accidentally touches the metal casing (due to a fault), the Earth wire provides a low-resistance path for the current to flow to the ground. This causes a very large current surge, which blows the fuse or trips the circuit breaker, immediately cutting off the power and making the appliance safe.

Answer:

The function of a fuse is to protect the appliance and the user from excessive current. It is a safety device containing a thin wire designed to melt and break the circuit if the current flowing through it exceeds a certain safe limit.

Answer:

If too much current flows through the fuse (e.g., due to a fault in the appliance or a short circuit), the thin metal wire inside the fuse heats up rapidly and melts. This breaks the circuit, stopping the flow of current immediately, and preventing damage to the appliance from overheating or further electrical faults.

Answer:

It is important to use a fuse with the correct current rating to ensure effective protection.

• If the fuse rating is too high, it won't blow quickly enough in the event of a fault, and the appliance could be damaged or become a fire risk.
• If the fuse rating is too low, it might blow unnecessarily during normal operation, preventing the appliance from working. The fuse rating should be slightly higher than the normal operating current of the appliance.

Answer:

First, calculate the normal operating current of the kettle using the formula P=IV:

$I=P/V$

$I=920W/230V=4A$

Since the normal operating current is 4 A, the fuse chosen must be slightly higher than this value but as close as possible.

Therefore, a 5 A fuse should be chosen.

Answer:

Calculate the normal operating current:

$I=P/V$

$I=60W/230V \approx 0.26A$

The fuse must be slightly higher than 0.26 A.

Therefore, a 3 A fuse should be chosen.

Answer:

The Earth pin is longer so that it makes contact with the socket first when the plug is inserted and breaks contact last when the plug is removed. This ensures that the appliance's metal casing is always earthed before the Live and Neutral connections are made, providing an extra safety measure.

Answer:

• Longest pin at the top opens the socket covers as the plug is pushed in.
• Insulation around the bottom of earth and live pins to insulate the user from shock when removing the plug.

Answer:

You should never do this because it defeats the safety purpose of the fuse.

A piece of wire or a fuse with a much higher rating will not melt and break the circuit when a fault occurs. This means that excessive current could continue to flow, leading to:

• Overheating of the appliance or wiring, causing fire.
• Risk of electric shock if the Live wire touches the casing.
• Damage to the appliance.

Answer:

A circuit breaker is more likely to have operated.

Reason: Circuit breakers are now more common because, unlike fuses that need to be replaced after they blow, circuit breakers can simply be reset (switched back on) once the fault has been identified and fixed. They also tend to react faster and are more reliable.

Answer:

It is crucial because:

• Safety: Incorrect wiring means safety features (like the Earth wire) might not work, or components could be live when they shouldn't be.
• Functionality: Appliances might not work correctly or at all.

If the Live and Neutral wires were swapped:

• The appliance might still work (as AC can flow in either direction for basic components).
• However, the fuse would now be on the Neutral side, and the switch inside the appliance (which is usually on the Live side) would now be on the Neutral side. This means that even when the appliance is switched "off," the Live wire inside the appliance would still be at high potential, making the appliance casing potentially dangerous (live) if a fault occurred. The fuse would still blow for an overcurrent, but the safety switch would be ineffective in isolating the live wire.