RCD Types
Installation · C&G 2365 Unit 203 · Premium section
A compares the current flowing out along the line conductor with the current coming back on the neutral. A difference means current is escaping — possibly through a person — and the device disconnects in milliseconds.
Modern loads complicate the picture: electronics can produce residual currents with DC components that an old Type AC device simply cannot detect. That's why device selection now matters — Type A for most modern circuits, Type F and Type B where inverters and variable-speed drives distort the waveform further.
Add (an and protection in one module) and questions about nuisance tripping and per-circuit protection, and this small topic earns its place in every modern exam.
Common questions
- Is there a free RCD Types quiz?
- Types sits in the Installation section, which is part of TradeTraining Premium — but the app is free to start, sample questions are open to everyone, and the free sections cover the fundamentals first.
- Where does RCD Types sit in the City & Guilds scheme?
- Types maps to C&G 2365 Unit 203. On TradeTraining it lives in the Installation section as bite-size lessons with practice questions.
- What is the difference between an RCD and an RCBO?
- An detects residual (leakage) current only — it won't trip on a simple overload. An combines that residual protection with overcurrent protection in a single device, so one faulty circuit trips alone instead of dropping every circuit sharing an RCD.