What it is called, by market
One concept, four markets. Where a name means something else locally, the card says so rather than leaving you to find out on site.
United Kingdom
Close, not identicalRCD
also residual current device, trip switch, RCBO, RCCB
An RCD alone does not protect against overload; an RCBO combines residual-current and overcurrent protection in one module, which is what a modern consumer unit mostly contains.
Australia
Close, not identicalRCD
also safety switch, earth leakage circuit breaker, RCBO
As the UK. Safety switch is the common non-trade term and appears in consumer-facing documents and in tenancy requirements.
United Statesyours
Close, not identicalGFCI
also ground fault circuit interrupter, GFI, AFCI, receptacle GFCI
Same principle at a lower trip threshold — nominally around 5 mA against the 30 mA typical of a UK RCD — and commonly built into a receptacle rather than into the panel. AFCI is a different device detecting arcing, with no direct UK equivalent.
Canada
Close, not identicalGFCI
also ground fault circuit interrupter, AFCI, dual function breaker
As the United States under Canadian Electrical Code rules, with dual-function breakers combining ground-fault and arc-fault detection.
The governing standard, by market
United Kingdom
BS 7671 (IET Wiring Regulations)
Where additional protection by RCD is required, the 30 mA threshold, and disconnection times.
United States
NFPA 70 (NEC) Article 210.8
Locations requiring GFCI protection for personnel, and the class of device required.
Calculators for this
Each works in either measurement system, and the terminology on the page follows whichever market you have selected.
Frequently asked questions
- Is a GFCI the same as an RCD?
- The principle is identical and the numbers are not, which matters when reading a specification across markets. Both measure the imbalance between line and neutral current and disconnect when it exceeds a threshold, on the reasoning that the missing current has gone to earth through something — possibly a person. An American GFCI protecting personnel trips at roughly 5 mA; a British RCD providing additional protection trips at 30 mA. The 30 mA figure is not chosen to prevent a shock but to disconnect fast enough that the shock is survivable, which is a different design intent, and it is why British practice pairs the RCD with strict earthing and disconnection-time rules rather than relying on the device alone. Reading one market's threshold into the other's system produces either nuisance tripping or a device that does not do what the code assumed.
- What is the difference between an RCD, an RCBO and an MCB?
- They protect against three different failures, and a board can contain all three. An MCB — miniature circuit breaker — protects the CABLE against too much current, whether from an overload or a short circuit; it does nothing about a current leaking to earth. An RCD protects PEOPLE against that leakage, and does nothing about overload, so an RCD on its own still needs overcurrent protection somewhere upstream. An RCBO is one module doing both jobs for one circuit, which is why a modern consumer unit populated with RCBOs loses only the affected circuit when something trips, where an older board with one RCD covering half the installation loses everything on that side. The American equivalent split is a standard breaker against a GFCI breaker against a dual-function breaker.
- Why does an RCD trip when nothing appears to be wrong?
- Because leakage is normal in small amounts and it accumulates. Every appliance with a filter, a heating element or a long cable run leaks a fraction of a milliamp to earth as a matter of design, and an RCD covering many circuits sums all of it. Add a damp exterior socket, an old immersion element, a freezer and a run of outdoor lighting, and the standing leakage can sit close to the trip threshold — so the device trips on the next small addition rather than on a fault. That is the diagnostic pattern: a trip that follows switching something on has a suspect, while a trip that happens with nothing changing, or only in wet weather, is usually accumulated leakage plus moisture. It is also the practical argument for splitting circuits across separate devices rather than putting one RCD in front of everything.