Fuses and Earthing

Question 1

What causes surges?

Answer 1

Something changes in a circuit, like when you turn an appliance on or off, or because of a fault in the circuit or appliance.

Surges can damage appliances, cause fires, and cause electric shocks.

Question 2

How do fuses and circuit breakers ensure safety and reduce the risk of surges?

Answer 2

They break the circuit whenever the current gets too high.

Question 3

What is a fuse?

Answer 3

A very thin piece of wire that’s connected to the live wire. If there’s a surge, a huge amount of current will flow through the live wire, and hence flow through the fuse. This causes the wire of the fuse to heat up rapidly, and because it’s so thin, it will melt, which then breaks the circuit meaning no more current can flow through it.

You can get fuses in a range of different ratings depending on what current you want to break the circuit. The fuse always wants to be a couple of amps above the rating of your appliance.

Question 4

What are the pros and cons of fuses?

Answer 4

Pros:

• Simple
• Cheap

Cons:

• One time use
• Might have to be replaced frequently

Question 5

What are circuit breakers?

Answer 5

They break the circuit whenever there is a surge, however, they don’t get permanently damaged. Rather, they just get tripped and turn off the circuit. This means that they can easily be reset rather than having to be replaced.

Question 6

What are the pros and cons of circuit breakers?

Answer 6

Pros:

• They can be used multiple times
• They don’t get permanently damaged after use

Cons:

• More expensive than fuses

Question 7

What are the dangers of the live wire coming loose and touching the casing inside an appliance? How is this prevented?

Answer 7

If a person touched the casing anywhere on the appliance after the live wire came loose, they would get a big electric shock.

One way to prevent this is by earthing, which is where an earth wire provides an alternative pathway for the current to flow away, so that any electricity is diverted through the earth wire rather than coming through us.

Question 8

What does it mean to double insulate an appliance?

Answer 8

The entire appliance will be covered in a plastic casing, so that there is no exposed metal parts that we can touch. Since plastic doesn’t conduct electricity, we can’t get an electric shock from touching it.

If an appliance has double insulation, it won’t require an earth wire. This means it will only have a **live wire* and a neutral wire.