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GCSE Physics · key term
A safety conductor that connects exposed metal parts of an appliance to earth and normally carries no current.
Used by AQA, Edexcel and OCR
Specification 4.2.3.2 · Paper 1
The green-and-yellow striped safety conductor that is connected to exposed metal parts in an earthed appliance and normally carries no current.
Revise: Mains electricityThe earth wire is at 0 V, and the neutral wire is normally at or close to 0 V. The live wire has an alternating potential relative to earth. For the UK mains supply, its potential difference from earth is about 230 V.
Specification 10.38, 10.40, 10.41 · Paper 2
When explaining an earth fault, give the full sequence: live touches the metal case → the earth wire provides a low-resistance path → a large fault current flows → a fuse melts or a circuit breaker disconnects the supply.
Do not say that current normally flows through the earth wire. It should carry current only when there is a fault.
Trace the fault sequence in order: live wire touches the metal case → a large current flows through the earth wire → the fuse melts or the circuit breaker trips → the supply is disconnected.
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A safety wire connecting the metal case of an appliance to the ground, providing a low-resistance route for fault current.
The earth wire provides the route; a fuse or circuit breaker disconnects the circuit.
A safety wire connected to Earth and maintained at approximately 0 V; it does not normally carry current.
Specification P8.2i, P8.2j · Paper 2 (Foundation), Paper 4 (Higher)
A protective mains wire that connects exposed metal parts of an appliance to earth, where fitted.
Revise: Mains wiresThe earth wire has a different job. Where an appliance has an exposed metal casing that needs earthing, this wire connects the casing to earth. It is a protective path and normally carries no current.
A conductor connected to the ground, providing a path for current if a fault connects a live part to it.
Paper 1, Paper 2
A safety conductor connecting an appliance's metal casing to earth; it normally carries no current but provides a low-resistance path during a fault.
Revise: Mains Electricity and Electrical SafetyThe earth wire, coloured green and yellow, is a safety connection. It is connected to the metal casing of an appliance and to earth, which is treated as 0 V. It is not part of the normal operating circuit, so it should not normally carry current.