AFDD
Arc Fault Detection Device
A protective device that recognises the electrical signature of dangerous arcing — the sputtering of a damaged cable or a loose terminal — and disconnects the circuit before the arc starts a fire. Ordinary and cannot see these faults, because a series arc neither leaks current to earth nor draws obvious .
Where AFDD 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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- RCD TypesInstallation
- BS 7671 Amendment 4The Regs and Practice Papers
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- 18th Edition Exam — quiz previewPlus · The Regs and Practice Papers
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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.
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RCD — 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 entrySPD — Surge Protective Device
A device that diverts brief, high-voltage spikes — from lightning activity or heavy switching — safely to earth before they reach sensitive equipment. Usually fitted at or near the consumer unit, SPDs have moved from a luxury to an expected part of new installations as homes fill with vulnerable electronics.
Read the SPD entryMCB — Miniature Circuit Breaker
An automatic switch that turns a circuit off when too much current flows, whether a slow overload or a sudden short circuit. It has replaced the rewirable fuse in modern boards. Each one is chosen by its current rating, such as 6 A for lights or 32 A for sockets, and by its type: B for most home circuits, C or D where equipment draws a big surge as it starts.
Read the MCB entryA definition is a start. Using it in a real question is where it sticks.