domestic uses and safety Flashcards
In the United Kingdom, the domestic electricity supply is an alternating current (AC) with a frequency of 50 Hz and a voltage of 230 V.
Explain what the frequency and voltage of the supply represent.
Mains electricity is an ac supply. In the United
Kingdom the domestic electricity supply has a
frequency of 50 Hz and is about 230 V.
Explain why a three-core cable is used for electrical appliances and describe what each core is used for.
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Most electrical appliances are connected to the
mains using three-core cable.
What is the colour of the insulation for the live wire, the neutral wire, and the earth wire?
The insulation covering each wire is colour coded for
easy identification:
live wire – brown
neutral wire – blue
earth wire – green and yellow stripes.
b) Explain the purpose of each wire in the three-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
Explain why the potential difference between the live wire and earth is 230 V.
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).
Explain why the earth wire normally carries no current and under what conditions it might carry a current
The earth wire is at 0 V, it only carries a current if
there is a fault.
Explain the difference between direct and alternating
potential difference.
DC has a constant direction of flow.
AC changes direction periodically.
Explain that a live wire may be dangerous even when
a switch in the mains circuit is open
The live wire is always at a high potential (230 V in the UK), even when the switch is open.
Open switch: Disconnects the flow of current, but the live wire can still carry a dangerous potential.
If a person touches the live wire, they could complete the circuit by connecting to the ground (earth), leading to an electric shock.
The earth wire is designed to provide a safe path for current in case of a fault, but the live wire is still dangerous.
Safety: Always ensure the circuit is properly isolated, and handle electrical appliances with care, even when the switch is off.
explain the dangers of providing any connection
between the live wire and earth.
Potential Difference: The live wire carries a high potential (about 230 V in the UK), while the earth wire is at 0 V (earth potential).
Short Circuit Risk: If a connection is made between the live wire and earth, it creates a short circuit, allowing current to flow directly from the live wire to the earth, bypassing the load (such as an appliance).
Large Current Flow: A short circuit leads to a large current flowing through the circuit. This can overload the system, causing the circuit breaker or fuse to trip to prevent further damage, but the sudden surge of current can still be dangerous.
