P2 - Household Electricity Flashcards
What is direct current?
Where the current flows in one direction only for example in batteries.
What is alternating current?
Where the current changes direction for example mains electricity.
What are the properties of mains electricity?
Potential difference is 230V.
Frequency is 50Hz.
This is an oscilloscope reading. What does it show?
Direct Current
This is an oscilloscope reading. What does it show?
Alternating Current
What happens if we use a diode on an AC oscilloscope?
Trace on only one half.
What colour is neutral wire?
Blue.
What colour is live wire?
Brown.
What colour is earth wire?
Green and yellow.
Describe an electrical wire.
3 copper wires inside - live, neutral and earth. (Earth not needed if the object is double insulated. Surrounded by a plastic insulator.
What is the live wire for?
Carrying electrical supply.
What is the neutral wire for?
Carrying electrical supply.
What is the earth wire for?
Safety, particularly for devices which have a metal case in conjunction with the fuse.
Describe how a fuse works.
Fuses have different current ratings (3A, 5A, 13A). If the current is higher than this rating then the fuse wire will melt.
Where should fuses always be placed?
Fuses should always be placed in series with the live wire and the appliance so if the fuse melts then the appliance is cut off from the live.
What is the danger of using a fuse with an incorrect current rating?
If a fuse with a too high current rating is used then the fuse will not melt when it should.
If a fuse with a too low current rating is used then the fuse will melt even at safe levels for the appliance.
What does a fuse protect against?
It protects the appliance and prevents fires.
What are circuit breakers?
Circuit breakers are electromagnetic switches which open (trip) when there is a fault which prevents the current in the live wire from flowing.
Where should fuses always be placed?.
Fuses should be placed in series with the live wire so if the current is too large then the magnetic field will be strong enough to pull the switch contacts open. This stops the current.
What is an advantage of a circuit breaker over a fuse?
1) They work faster.
2) They can be reset.
What does RCCB stand for?
Residual Current Circuit Breaker
How does an RCCB work?
It detects a difference in current between the live and neutral wire. They are A LOT faster than regular circuit breakers or fuses.
What does earthing protect against?
Electric Shocks. If there was a fault and the live wire came into contact with the metal casing of the appliance and you touched it then the current would go through you to get to ground. Earthing would prevent this.
How does earthing protect you?
If there was a fault and the live wire touched the metal case
The current travels through the metal casing to the earth wire
The earth wire has a low resistance which would cause the current to increase
This would melt the fuse or trigger the circuit breaker and prevent electrocution.
What is double insulation?
Where the case of an appliance is made of an insulator so there is no need for an earth wire.
