ADS
Automatic Disconnection of Supply
The standard protective measure in UK installations: , protective bonding and a protective device working together so that a fault to earth causes disconnection within a prescribed time. If any leg fails — poor earth path, missing bond, wrong device — the fault can sit live on touchable metalwork instead of clearing.
Where to look it up: BS 7671 Chapter 41.
How the ideas connect
ADS names the protective measure as a whole, rather than a single device. The earth path, protective bonding and protective device work together; recognising one part does not explain the whole measure.
Where ADS fits in the learning path
The Installation section covers these units:
- Wiring Systems & Enclosures
- Cable Selection & Circuit Design
- Earthing, Bonding & Consumer Units
Curriculum mapping: C&G 2365 Units 203/204/305.
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This section is on the Plus path. Lesson availability depends on content review and your learning path.
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1. Read it in context
- Earthing & BondingInstallation
2. Try recalling, then explore practice
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Follow a topic above to explore how the term is used, then use the learning entry below to find your path.
3. Return to the meaning
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Connecting an installation's exposed metalwork to earth and back to the supply source. That gives fault current a deliberate low-impedance path home, turning a live casing into a large, brief fault current that the protective device can detect and disconnect — without it, the casing simply stays live.
Earthing
Read the Earthing entryCompare related terms
Open a meaning to compare its role with ADS, or follow its full entry.
Earthing
Connecting an installation's exposed metalwork to earth and back to the supply source. That gives fault current a deliberate low-impedance path home, turning a live casing into a large, brief fault current that the protective device can detect and disconnect — without it, the casing simply stays live.
Read the Earthing entryZs — Earth Fault Loop Impedance
The total opposition to current around the loop a fault current would travel. That loop runs from the supply, along the line conductor to the fault, and back through the protective conductor and the earthing. It is the supply's own part (Ze) plus the circuit's R1 + R2, the resistance of its line and protective conductors. A low Zs lets a big fault current flow, which trips the protective device quickly, so electricians measure it and compare it with the maximum allowed for that device.
Read the Zs entryFault protection
Protection that operates when basic protection has failed and a live conductor has reached touchable metalwork. In UK practice it usually means automatic disconnection of supply: earthing and bonding hold the touch voltage down while the protective device removes the supply within its required time.
Read the Fault protection entryRCD — Residual Current Device
A safety switch that compares the current going out on the line conductor with the current coming back on the neutral. If they differ, current is leaking somewhere it should not, possibly through a person, and the RCD cuts the supply in a fraction of a second. Most socket circuits in UK homes need RCD protection, usually rated at 30 mA.
Read the RCD entryA definition is a start. Using it in a real question is where it sticks.