Lesson 4 Fuses

Starter: Any electrical circuit usually has one or more fuses in it. Why? What would happen if there were no fuses?

Input: Safety with Fuses.

If an appliance such as a light or a heater stops working, it is probably because the fuse has blown. There are 3 main types of fuse in use today - cartridge, rewirable and the most modern type, miniature circuit breakers. Some appliances have their own fuses (usually in the plug), so this should be checked first. Otherwise, check whether the main fuse has gone. The main fuses are normally in a switch box or fuse box at the point where the main electricity supply cable enters the building usually near the front door. Before checking these fuses, turn off the main switch. Remove and examine the fuses one by one. Which the cartridge fuses the simplest thing to do is to take out the old fuse and try a substitute fuse of the correct amp rating, of course.

Then test the appliance, with reliable fuses look for wire breaks or scorch marks on

the fuse car­riers. Remove the old wire, fit new wire round the retaining screws and

tighten the screws. Replace the fuse carrier and see if the appliance works. If a fuse

continues to blow, do not fit another fuse, but get an electrician to check the

appliance and the circuit for possible faults. Never attempt to use a fuse of a higher

rating.

Gathering Information

Step 1.

From Input, find answers to these questions :

What does a fuse do?

What are the three types of circuit protection?

Where are fuses located in a circuit?

How should you check a cartridge fuse?

What tells you whether a reliable fuse has blown?

What is the first thing to do when checking a main fuse?

What should you do if a new fuse blows immediately?

Step 2.

Replace the words and expressions in bold type with ones of similar meaning from the Input.

a) When a rewirable fuse blows, it burns the carrier.

b) Always switch off, before examining the main fuses.

c) When you have put the fuse back, try the appliance again.

d) There is probably something wrong with the circuit, if the fuse blows again.

e) With a reliable fuse you must take out the old wire, then put new wire round the screws and do up the sewers.

Step 3

a) What are the advantages and disadvantages of the different types of fuses mentioned?

b) Why shouldn’t you fit a fuse of a higher rating?

Step 4. Warnings

Do:

Always turn off the main switch

Always fit a fuse of the correct rating.

Don’t:

Don’t fit a fuse of

Do not do a higher rating.

Make warnings from these cues:

a. Check the amp rating of an appliance

b. Handle electricity with wet hands

c. Repair appliances with the power on

d. Use insulated pliers

e. Put too many plugs to one outlet

f. Use old cables or flexes

g. Have a supply of fuse wire available

h. Join wires carelessly.

Step 5. Conditions and Instructions

Look at these examples:

If an appliance stops working, check the fuse.

If a fuse continues to blow, do not fit another fuse.

Choose a condition from A and an instruction from B to make sentences like those in the examples :

A An appliance stops working. You do not know where the fuse box is. You haven’t got the correct amp fuse. You need to check the main fuse. You know little about electricity. One of the circuit breakers is switched off. Check whether one of the switches is off. Look near the front door. Check the appliance fuse first. Use a higher amp rating. Check the circuit or appliance. Try to fit electrical faults yourself. Switch the circuit on again.

B The appliance has got its own fuse. The fuses are reliable. The fuse blows again immediately. The fuse continues to blow. You have got circuit breakers. The appliance has not got a fuse. Check the main fuses. Leave the fuse box switched on. Fit another fuse. Check the fuse. Fit a new fuse. Look for scorch marks.