Domestic Electricity Flashcards
How does mains electricity get to houses?
- A power station generates heat to make steam
- The steam rotates a turbine in an electromagnetic field
- An emf is produced through electromagnetic induction
- This emf is alternating current at 50Hz
- A transformer steps up the voltage for long-distance transfer
- Near the destination, another transformer steps the voltage down to 230V rms
- The electricity enters the house through the fuse box and distribution board
What circuits is the domestic wiring split into?
- Ring circuits
- Radial circuits
- Lighting
What are ring circuits?
Power travels both ways around a ring circuit. All sockets are usually connected in this way, therefore if one has a fault, the otherss in the ring still work. Ring circuits have a common neutral and the fuse is connected in the live. They are usually located in specific areas of a house. This makes each area easier to repair if there is a fault.
What are radial circuits?
Appliances that require a large amount of power may get individual circuits radiating from the distribution box. Examples include electric showers, washing machines and cookers. Each radial circuit has its own neautral and fuse in the live.
How do lighting circuits work?
Generally lighting circuits are separated into distinct areas of the house. All the lights would be connected in parallel, so individual faults do not cause the rest to fail.
What are some faults/safety features?
- Switches
- Fuses
- Minature circuit breakers (MCBs)
- Residual current devices (RCDs)
- Earthing
- Plugs
What is the purpose of switches?
Rather than having all appliances constantly connected to the live, switches are used to connect or disconnect an appliance when needed.
What is the purpose of fuses?
Fuses are connected in the live and protect against too much current flowing. Too much current will heat and melt the fuse, which breaks the circuit. The value of a fuse is slightly above the expected current value.
What is the purpose of minature circuit breakers?
MCBs are essentially resettable fuses. The live wire is wound around an iron core, making it an electromagnet. When too much current is present, it is pulled against a switch, breaking the circuit. This switch is levered against a spring, meaning it takes a preset current to pull it away.
What is the purpose of residual current devices?
RCDs act like a transformer. The live and neutral wires wrap around an iron core just like the wires in an transformer. The live wraps around one side and the neutral around the other side. Alteranting current induces a magnetic field and at the same time an opposite a.c. of the same value flows back and forth in the neutral, inducing an equa; but opposite magnetic field. This essentially cancels out the fields. If there is a fault in a wire, there is a difference between the fields, causing a relay (very fast switch) to be activated, cutting the current supply. RCDs act on speed, so are better at protecting people than fuses and MCBs.
What is earthing?
Earthing is the process of connecting parts of appliances to an earth wire. This way, if the live happens to touch the outside of the appliance, it will send its current to earth rather than through the person (people have higher resistance). Another type of earthing is called ‘bonding’, where pipes carrying liquids are connected to earth, to stop electric shocks travelling through them.
How do plugs work?
A plug contains a:
- Brown live wire, always connected to the fuse (Left)
- Blue neutral wire, carries current but with almost neutral voltage (Right)
- Green and yellow earth wire, connected to the earth (Top)
The casing of the plug is plastic, which is a good insulator. The earth pin is longer than the others and acts as a safety feature by opening up the other two pin sockets in the wall.
What is the kilowatt-hour?
A unit of electricity consumption used by electrical energy providers to measure how much electricity is to be paid for.
