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An Alternating Current ( A.C )
Constantly changing direction or alternates in direction, 50 times/second
Mains Electricity
It is the electricity supply from power stations to our homes and uses Alternating Current (A.C)
Direct Current (DC)
Flows in one direction only and has a consistent value.
When is D.C current provided?
By batteries or DC adaptors/transformers that plug into the main supply.
What can a CRO do?
We can see the difference between AC and DC.
Why is alternating current used in mains supply?
it allows the voltage to be changed in transformers and transmitted over long distances with little energy losses.
What do mains electricity generate from power stations?
they're supplied to all Malta households via National Grid.
A household circuit is made up in two parts?
A lighting circuit and a ring main power circuit (for high power appliances)
Each power point is also protected by?
by a fuse inside the plug.
What are the 2 wires called coming from the power station?
Live and Neutral wires
The third wire is called?
The third wire E is connected to Earth.
Each lightning point is connected in parallel because?
If one is faulted the others would work normally.
How does main electricity enter a house?
main electricity enters the house via Live wire (L)
The live wire carries electricity of?
240V and therefore it is very dangerous, that it could kill somebody.
The Neutral wire is also supplied?
From the power supply, it is used to complete the circuit and for the energy supplied in the live wire given to the household, the current travels back via the neutral wire.
What is the earth wire used for?
it is used for safety, and it is to be connected with the metal casing of the appliance and only carries a current when there is fault, so the fuse can melt.
if fault develops in an appliance and the live wire touches the metal case-
Large current flow through the live wire to the earth wire and the fuse breaks which makes the appliance safe.
Where must the fuse be placed?
it must be placed in the live wire so it can isolate the appliance from the live wire.
What do the earth wire and fuse do?
together they protect the appliance and the user from an electrocution.
What is double insulation?
Some appliances are double insulated, which means they have a plastic insulating case and therefore do not require an earth wire connected to them.
What is the symbol of double insulation appliances?
Appliances such as hairdryers are marked with the symbol -
Note
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