P4 - Plugs and Fuses Flashcards
What is the purpose of the live wire?
The live wire carries the voltage, it alternates between a high +ve and -ve voltage of about 230 V.
What is the purpose of the neutral wire?
The neutral wire completes the circuit, electricity normally flows in through the live wire and out the through the neutral wire.
What is the purpose of the Earth wire?
These are for safety and work together.
What colour is the Earth wire?
Earth wire is Green/Yellow.
What colour is the neutral wire?
The neutral wire is blue.
What colour is the live wire?
The live wire is Brown.
Why must all appliances with metal cases be earthed?
All appliances with metal cases must be earthed to reduce the danger of electric shock.
What does “Earthing” mean?
Earthing means the case must be attached to an earth wire.
- An earthed conductor can never become live, the earth wire stops the appliance becoming live.
What does it mean when an appliance is “double insulated”?
It means that that appliance has a casing that is non conductive, e.g. plastic, it is then considered double insulated.
- Anything that is double insulated does not require an Earth wire as it cannot become live.
What is an example of how the Earth wire acts as a safety feature?
If a fault develops in which the live wire somehow touches the metal case. then because the case is earthed, a big current flows in through the live wire through the case and out down the earth wire.
How does the fuse protect the user?
- The surge in current travelling through the earth wire due to the case becoming live, will result in the fuse being “blown” and causes the wire inside to melt. This cuts off the live wire supply because it breaks the circuit.
- This isolates the whole appliance, making it impossible to get an electric shock from the case.
Besides preventing the user from being shocked, what are some other ways in which fuses and earth wires protect the user?
- It sops flex overheating, which could cause a fire.
- It prevents further damage to the appliance.
What is a key difference between fuses and circuit breakers?
- Circuit breakers work like a fuse, however they can be reset.
- Fuses break when they “Blow” and have to be replaced.
How should fuses be rated & why?
Fuses should be rated as near as possible but just higher than the normal operating current. If they were a lot higher , they wouldn’t blow when the live wire touched the case or when a fault developed.
What is the formula for electrical power?
Power = Voltage X Current.
