It is extremely important to choose the correct size fuse for an electrical appliance.

In order to calculate the right size of fuse then we need to revise the following formula:

The electrical power of an appliance such as a fridge depends upon:

  • Its working voltage;
  • The current that it draws from the mains.

Formula:

Examples

  1. An electric iron works from the mains voltage (240V). If its power is 720 Watts then calculate it’s current. ______
  1. (a) An electric lamp uses energy at the rate of 60watts from a 240 V supply. Find the current it draws from the supply. ______
  1. A kettle has a power rating of 2000 W at 240 V. Calculate the current that this device draws from the mains. ______

Common fuses in use today are:

In order to choose the right size fuses then do the following steps:

Use the Equation P = V x Ito calculate the current in the device.

Choose a fuse value which has the next highest rating.

Example:

1. A washing machine is labelled 2400 W, 240V. Calculate the right size fuse for the plug.

______

2. A table lamp is labelled “The maximum size light bulb with this appliance is 150 W, 240V”. Calculate the right size fuse for the lamp’s plug.

______

Complete the following table:

  1. Complete the following sentences:

(a)The power (in W ..….) in an electrical circuit is equal to the current (in . . . . . ) multiplied by the ...... (in ...... ). [2]

(b) When wiring a fused plug, the brown wire should always go the …………. terminal, the blue wire should go to the ……………….. terminal and the yellow-green wire should go to the …………….. terminal. [3]

(c)The Earth wire should always be connected to the ………………. of an appliance. [1]

(d)The Earth wire provides a ………… ....………….. path to earth for the current. [2]

(e) A fuse (or switch) should always be placed in the ………………… wire of the mains circuit. [1]

(f)When the current flowing into a device ……………...... a certain value the fuse …………………………. which breaks the …...... causing the current to stop flowing. [3]

(g) In general, thin power leads heat up very quickly and should therefore have a fuse with a ……………………. current rating. [1]

(h) The choice of fuse for a plug depends upon the size of the …………………. entering the appliance and the ………………… of the power lead. [2]

  1. (a) A vacuum cleaner is labelled 240V and 500W. When connected to the main supply how much current does it take? ______[2]

(b) What size fuse should befitted to the plug of this device? ______[1]

  1. The diagram shows the inside of a 3-pin plug.

(a) What is the colour of each of the wire:

A ______

B ______

C ______

[3]

(b) Which of the wires is the Earth wire? ______[1]

(c) What is the name of component D? ______[1]

(d) What does it do? ______[2]

  1. What size fuse (3A or 13A) should be used in a plug connected to a 150W TV set when plugged to the mains? ______[2]
  1. Complete the following table: