Household Electricity And Fuses (T2)

Question 0

A fuse is also described as…

Answer 0

…a “sacrificial wire”

Question 1

What is the standard voltage that mains systems run at in UK?

Answer 1

Around 230V

Question 2

How does a basic fuse wire work?

Answer 2

If too much current goes through the circuit, the fuse wire will overheat and melt, breaking the circuit

Question 3

Why do we need a fuse?

Answer 3

When we run a household circuit the amount of current must be controlled as different household appliances require differing amounts of energy flowing through them

Question 4

Whilst current is the flow of electrons around a circuit think of voltage as…

Answer 4

…the energy carried by those electrons

Question 5

The household appliances that contribute most to your electricity bill are the ones that…

Answer 5

…use a lot of power for long periods of time

Question 6

Some examples of household appliances and their energy consumption…

Answer 6

• a kettle or shower are HIGH POWER devices but not turned on for too long so do not cost much to run
• fridges, freezers and lights are often used for long periods but don’t use a lot of power so do not cost much to run
• heaters and immersion heaters consume several thousand watts and are often turned on for long periods, so their total energy consumption is very large

Question 7

In what unit do electricity companies give energy consumption?

Answer 7

Kilowatt hours (kWhr)

Question 8

Approximately how much do electricity companies charge in pence?

Answer 8

15p / kWhr

Question 9

What equation would you use to calculate the cost of running a household appliance?

Answer 9

Cost in pence = power in kW x time in hours x cost per kWhr

Question 10

What do you do to convert watts into kilowatts?

Answer 10

Divide by 1000

Question 11

How do you calculate your electricity bill from your meter readings?

Answer 11

Subtract the the previous reading from the current reading then multiply that figure by the cost per unit

Question 12

List four hazards that can occur with household electricity…

Answer 12

• frayed or damaged cables
• long cables
• water
• metal objects

Question 13

What are the three main fuses found in UK plugs?

Answer 13

3A, 5A and 13A

Question 14

What fuse would be needed for a 750W hairdryer?

Answer 14

I = P / V

750W / 230V = 3.26

Answer = 5A fuse

Question 15

What fuse would be used for a drill rated at 500W?

Answer 15

I = P / V

500 / 230 = 2.17A

Answer = 3A fuse

Question 16

What is an RCCB?

Answer 16

• a RESIDUAL CURRENT CIRCUIT BREAKER
• turns off current automatically if it exceeds a set limit
• switches off the whole circuit if more current is going out the live terminal than returning to the neutral one
• this happens if there is a fault casing the current to leak to earth and is designed to prevent electrocution, something a fuse does not do
• turn off current much faster than a fuse

Question 17

What is an Earth pin?

Answer 17

An earth pin is connected to the metal casing of certain appliances so that in certain circumstances, should a fault occur, the current can run out and down the earth pin to a plate buried in the ground, as opposed to flowing through the casing itself and into anyone touching it

Question 18

Why is an earth pin needed and how does it work?

Answer 18

Some appliances come with a metal casing, eg: fridges and washing machines. If a fault occurs causing a live wire inside to touch the casing, the earth pin provides the current with an easy route away from the casing, down the wire and into the earth. The current will have two options; go through the casing and into the person touching it (many thousands of Ohm’s resistance) or down the earth wire into the ground (almost zero resistance).
It will always choose the second, easier option.

Question 19

What does it mean if an appliance is double insulated?

Answer 19

When an appliance is made of plastic casing, and the components inside are covered in plastic themselves. This gives two layers of insulation between the live wires inside and the outer plastic casing.

Question 20

What is an LED?

Answer 20

• a LIGHT EMITTING DIODE
• a device that only allows current to flow in one direction and when this happens, it lights up
• they use very little current or power compared to filament light bulbs
• they must be connected the right way round. In a circuit diagram the arrow in the symbol must be pointing in the same direction as the current flow

Question 21

How do light bulbs with filaments work and are they energy efficient?

Answer 21

The current flows through a filament to the point where it is white hot and creates light.
This is extremely wasteful in terms of energy.

Question 22

What are CFL’s and why do they use a small amount of energy?

Answer 22

CFL stands for Compact Fluorescent Lamp, also know as an energy saving light bulb. Like LED’s, they produce very little heat, therefore using little energy in the process.

Question 23

Briefly describe the set up of a standard mains supply.

Answer 23

• electrical energy usually enters homes through an underground cable which is connected to an electricity meter measuring the amount of electrical energy used
• the cable is connected to a consumer unit or fuse box which contains fuses or circuit breakers
• most of the wires leaving the fuse box or consumer unit are connected to ring main circuits, hidden in the floors and walls around each room
• individual appliances are connected to these circuits using plugs

Question 24

What is a ring main circuit?

Answer 24

The circuits hidden in the walls and floors surrounding rooms in the home.
Appliances are attached to the circuit by plugs.

Question 25

How many wires are usually used in a ring main circuit and what do they do?

Answer 25

A ring main circuit usually consists of three wires - live, neutral and earth.
The live wires provides the path along which the electrical energy from the power station travels.
The neutral wire completes the circuit.
The earth has no current flowing through it and is there to protect you if there is a fault.

Question 26

In mains circuits, switches should always be included in which wire and why?

Answer 26

The live wire, so that when the switch is open no electrical energy can reach an appliance.
If the switch is included in the neutral wire, electrical energy can still enter an appliance and possibly cause electric shock.