Mains Electricity 

- The electricity supplied to homes, businesses, factories, etc.
- It is supplied from power stations and travels to us via the National Grid, a grid of pylons and wires.
- Mains electricity in the UK is supplied at 230 V of a.c.
→ The current shifts from a positive to a negative direction, 50x per second = 50 Hz.

Frequency = Number of times per second mains voltage changes from positive to negative and positive again.

A.C. and D.C. (Alternating Current and Direct Current)

- A.C. switches from positive to negative.
Advantage: Can be used to transmit electricity from power stations at very high voltages.
→ Less energy is lost by the overhead cables in the National Grid.
- Some electrical devices need D.C. (direct current) to only flow in one direction.
- Plugged into mains, a rectifier used in a circuit sometimes supplies D.C., so these devices may use batteries instead.

- Earth = No potential → 'Zero potential'
- There is no potential difference across points of Earth, and there is no overall charge.

Three Pin Plugs

- The live and neutral wires carry current in normal use.
- A wire connects each pin.
- Copper makes up each wire.

Safety checks when wiring a plug

1) No damage—no loose bits of wire
2) Have the correct fuse
3) Correct plug for country

Hazards

Damaged insulation: Contact with wire: e.g., gaps in insulation → electric shock/fire hazard by creating a short circuit.
Overheating of cables: High currents flowing through thin wire or rubble can cause wires to reach extremely high temperatures. This could potentially melt the insulation and ignite a fire.
Damp conditions: Water can conduct an electric shock. Wet electrical equipment can cause a current → voltage.
- Domestic electricity poses a potential risk due to its high voltage, with power lines reaching 20,000V per charge. At home, the voltage drops to 230V, leading to an increase in current and the risk of burns.

Fuses

- A thin piece of copper wire, which overheats and melts if the current is too high, protects the circuit from breaking when the current is too high.
- Must be connected to live wire—it comes into contact.
- The current rating should be slightly higher than the current rating used in the device; too high = Not as effective.
- Most common: 3A, 5A, and 13A.

Circuit Breakers

- Consist of an electromagnetic switch that breaks the circuit if current rises over a certain value.
→ It is more useful than a fuse because it can be reset and then used again, making it operate faster.
- If an RCD/RCCB detects a difference in current between the live and neutral wires, it opens the circuit breaker unit, thereby stopping current flow for power tools, they can be drills and lawnmowers.
The circuit breaker will not trip until the current exceeds a specific value.

Earthed appliances: Protects user from electric shock if a fault occurs, i.e., if a fault develops in an appliance and the live wire touches the appliance → becomes 'live'.

Earthing:

- If a fault develops in an appliance and the live wire touches the outside, causing a large current to flow from the live wire to the earth wire. This blows the fuses, the current stops flowing, and everything is safe.
- Earth wires have low resistance, so current surges through, breaking the fuse and disconnecting the appliance.
- If something breaks and touches the metal casing, it lets current into the earth. 
→ Earth wire connects to metal casing and carries current into earth outside.

- Double insulation: appliances with it have a symbol.
- Don't need an earth wire as they have a plastic casing, so it doesn't carry current.

Equations

1.

1) The electric kettle has a 2800W rating. What fuse is needed?

2) The lawn mower fits with a 5A fuse. What is the approximate power rating of the fuse?

P = IV → 5 x 230 = 1150W

2.