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The earth wire has green and yellow striped insulation. The earth wire is a safety wire that connects the metal case of an appliance to earth (0V). Free notes.
Three-Core Cables and Wire Identification is part of Domestic uses and safety in GCSE AQA Higher Physics.
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The earth wire has green and yellow striped insulation. The earth wire is a safety wire that connects the metal case of an appliance to earth (0V). Free notes.
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Use this lesson to stay inside Domestic uses and safety while connecting the detail back to the wider Electricity topic.
Read the core explanations from Three-Core Cables and Wire Identification before testing yourself from memory.
Your phone charger, kettle, and washing machine all connect to the wall socket using the same type of cable. But why does this cable contain three separate wires when a simple circuit only needs two? The answer lies in keeping you safe from electrocution.
Most electrical appliances connect to the mains using three-core cable. This cable contains three insulated wires, each with a specific colour and function. Understanding which wire is live, neutral and earth is important for electrical safety and for GCSE exam questions about plug wiring. You do not need advanced industry regulations here; you need the basic functions of each wire and why the earth wire helps to keep metal cases safe.
The insulation covering each wire uses colour coding for clear identification. This standardised system prevents dangerous mistakes during installation and repair work.
The live wire carries the alternating potential difference from the supply. In the UK, the mains supply is about 230 V. This wire is dangerous because touching it can drive a large current through your body. For GCSE, the key fact is the 230 V mains supply, not the peak value of the waveform.
The neutral wire completes the circuit. Current flows from the live wire, through the appliance, and returns via the neutral wire. The neutral wire stays at earth potential (0V), making it much safer to touch than the live wire.
The earth wire provides safety protection. Under normal operation, no current flows through it. However, if the live wire touches the metal case of an appliance, the earth wire provides a low-resistance path to earth, causing a large current that trips the circuit breaker.
Understanding the voltages between different wires is crucial for safety and exam questions. The earth wire and neutral wire are both at 0V potential, but the live wire alternates around 230V above earth potential.
Worked example: Calculating Potential Differences
In a domestic circuit, the live wire is at 230V and both neutral and earth are at 0V. Calculate the potential difference between: (a) live and earth, (b) live and neutral, (c) neutral and earth.
Answer: (a) 230V, (b) 230V, (c) 0V
This explains why touching the live wire is dangerous. The neutral wire is usually close to 0 V under normal conditions, but you should never treat it as safe because faults are possible and current can still be present. Always switch off at the mains before working on any electrical circuit or appliance.
The earth wire prevents appliances from becoming live during faults. If the live wire breaks and touches the metal case, the case would normally become dangerous at 230V. The earth wire prevents this by providing an alternative path.
When a fault occurs, the earth wire carries a large current back to the supply. This large current causes the fuse or circuit breaker to operate, disconnecting the supply and making the appliance safe.
Exam questions often test your understanding of wire functions and safety. Many students lose marks by confusing the roles of neutral and earth wires, or by incorrectly stating voltages.
Common mistakes include stating that the neutral wire is at 230V (it's at 0V), saying the earth wire never carries current (it does during faults), and forgetting that both neutral and earth are at the same potential in normal operation.
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Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.
The earth wire has green and yellow striped insulation. The live wire is brown and the neutral wire is blue, and this colour coding prevents dangerous mistakes during installation and repair.
The earth wire is a safety wire that connects the metal case of an appliance to earth (0V). If the live wire touches the case, the earth wire provides a low-resistance path, so a large current flows and the fuse or circuit breaker disconnects the supply.
The neutral wire completes the circuit by providing a return path for current back to the supply. Current flows from the live wire, through the appliance, and returns via the neutral wire, which stays at or close to earth potential (0V).
The potential difference between the neutral and earth wires is 0 V, because both are at the same potential, 0 V, in normal operation. The potential difference between live and earth, and between live and neutral, is 230 V.
The earth wire only carries current when there is a fault in the appliance. Under normal operation no current flows through it, but if the live wire touches the metal case, the earth wire carries a large current back to the supply.
If the live wire touches the metal case of an appliance, the earth wire provides a low-resistance path to earth. A large current flows through it back to the supply, which makes the fuse or circuit breaker operate, disconnecting the supply and making the appliance safe.
In a three-core cable, the live wire has brown insulation, the neutral wire has blue insulation, and the earth wire has green and yellow striped insulation. This standardised colour coding prevents dangerous mistakes during installation and repair work.
The potential difference between the live and neutral wires is 230V, because the live wire is at 230V and the neutral is at 0V. Live to earth is also 230V, while neutral to earth is 0V because both are at the same potential.
A three-core cable is the cable most electrical appliances use to connect to the mains. It contains three insulated wires, live, neutral and earth, each with a specific colour and function, and the third wire, the earth, is there for safety.
The live wire is the wire that carries the alternating potential difference from the supply to the appliance, about 230 V in the UK. It has brown insulation and alternates between positive and negative voltage relative to earth.
The potential difference between the live wire and the earth wire is 230 V. The live wire is at 230 V and the earth wire is at 0 V, and potential difference is the higher potential minus the lower potential.
The neutral wire should never be treated as safe to touch, even though it is usually close to 0 V under normal conditions, because faults are possible and current can still be present. The supply should always be switched off at the mains before working on a circuit.
Plugs have three wires because, as well as the live and neutral wires that a simple circuit needs, an earth wire is added for safety. The earth wire connects the metal case to earth and keeps metal cases safe if a fault occurs.
Common mistakes are stating that the neutral wire is at 230 V when it is at 0 V, saying the earth wire never carries current when it does during faults, and forgetting that neutral and earth are at the same potential in normal operation.
The live wire is at about 230 V in UK mains circuits, alternating around 230 V relative to earth potential. Touching it can drive a large current through the body, which is why it is dangerous.