Domestic Electricity Flashcards
Describe UK mains electricity.
UK Mains electricity is an a.c. supply. In the United Kingdom it has a frequency of 50 Hz and is about 230 V.
What colour is each wire in the UK 3 core cable?
Live wire – brown, neutral wire – blue, earth wire – green and yellow stripes.
Explain the relationship between the wires in the UK 3 core cable.
The live wire carries the alternating potential difference from the supply. The neutral wire completes the circuit. The earth wire is a safety wire to stop the appliance becoming live. The potential difference between the live wire and earth (0 V) is about 230 V. The neutral wire is at, or close to, earth potential (0 V). The earth wire is at 0 V, it only carries a current if there is a fault.
How can touching the live wire result in an electric shock?
Our bodies are at earth potential (0 V). Touching the live wire produces a large potential difference across our body. This causes a current to flow through our body, resulting in an electric shock.
Describe a safety mechanism in the live wire.
If an electrical fault causes too great a current, the circuit is disconnected by a fuse or a circuit breaker in the live wire. The current will cause the fuse to overheat and melt or the circuit breaker to switch off (‘trip’). A circuit breaker operates much faster than a fuse and can be reset.
How does the National Grid system efficiently transfer energy?
Step-up transformers are used to increase the potential difference from the power station to the transmission cables then step-down transformers are used to decrease, to a much lower value, the potential difference for domestic use. This is done because, for a given power, increasing the potential difference reduces the current, and hence reduces the energy losses due to heating in the transmission cables.
