P2.4 Using mains electricity safely and the power of electrical appliances

Question 1

46. Define a an alternating current (a.c.)

Answer 1

46. Current is constantly changing direction.

Question 2

47. What is the frequency and voltage of mains electricity in the UK?

Answer 2

50 hertz)and is about 230 V.

Question 3

48. Most electrical appliances are connected to the mains using a?

Answer 3

48. three-pin plug.

Question 4

49. Describe the structure of electrical cable.

Answer 4

49. Earth = yellow and green, Live = Brown and Neutral = Blue.

Question 5

50. Which wire is attached to the Fuse in a 3 pin plug?

Answer 5

50. Live (Brown)

Question 6

51. What happens if an electrical fault causes too great a current?

Answer 6

51. The circuit is disconnected by a fuse or a circuit breaker in the live wire.

Question 7

52. What happens when the current in a fuse wire exceeds the rating of the fuse?

Answer 7

52. It will melt, breaking the circuit.

Question 8

53. Some circuits are protected by Residual Current Circuit Breakers (RCCBs). What are they?

Answer 8

53. RCCBs operate by detecting a difference in the current between the live and neutral wires, this device operates much faster than a fuse.

Question 9

54. Some appliances are double insulated – what does this mean?

Answer 9

54. They have no earth wire connection.

Question 10

55. Describe how the earth wire and fuse together protect the wiring of the circuit.

Answer 10

55. When the live wire comes in contact with the metal case a large current flows. This current melts the fuse and breaks the circuit.