Household Electricity And Fuses (T2) Flashcards
A fuse is also described as…
…a “sacrificial wire”
What is the standard voltage that mains systems run at in UK?
Around 230V
How does a basic fuse wire work?
If too much current goes through the circuit, the fuse wire will overheat and melt, breaking the circuit
Why do we need a fuse?
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
Whilst current is the flow of electrons around a circuit think of voltage as…
…the energy carried by those electrons
The household appliances that contribute most to your electricity bill are the ones that…
…use a lot of power for long periods of time
Some examples of household appliances and their energy consumption…
- 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
In what unit do electricity companies give energy consumption?
Kilowatt hours (kWhr)
Approximately how much do electricity companies charge in pence?
15p / kWhr
What equation would you use to calculate the cost of running a household appliance?
Cost in pence = power in kW x time in hours x cost per kWhr
What do you do to convert watts into kilowatts?
Divide by 1000
How do you calculate your electricity bill from your meter readings?
Subtract the the previous reading from the current reading then multiply that figure by the cost per unit
List four hazards that can occur with household electricity…
- frayed or damaged cables
- long cables
- water
- metal objects
What are the three main fuses found in UK plugs?
3A, 5A and 13A
What fuse would be needed for a 750W hairdryer?
I = P / V
750W / 230V = 3.26
Answer = 5A fuse
What fuse would be used for a drill rated at 500W?
I = P / V
500 / 230 = 2.17A
Answer = 3A fuse
What is an RCCB?
- 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
What is an Earth pin?
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
Why is an earth pin needed and how does it work?
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.
What does it mean if an appliance is double insulated?
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.
What is an LED?
- 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
How do light bulbs with filaments work and are they energy efficient?
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.
What are CFL’s and why do they use a small amount of energy?
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.
Briefly describe the set up of a standard mains supply.
- 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
