RCCB / RCD / GFCI
Breaker
A device that quickly cuts power when it detects leakage current to ground, protecting against electric shock and fire hazards.
Schematic symbol
Switch (SPST)
How rccb / rcd / gfci appears in a circuit diagram.
Types & variants
Key specs
Trip current
mACurrent level at which the device trips (typically 10mA, 30mA, or 40mA).
Breaking capacity
kAMaximum fault current the device can safely interrupt without damage.
Response time
msTime to trip when leakage current exceeds threshold (typically <30ms).
Voltage rating
VMaximum system voltage the device is designed to protect.
Laws that govern it
- Kirchhoff's current law (KCL)ΣI(in) = ΣI(out)
The whole principle: current out on the line must return on the neutral. If they differ by 30 mA, that current is going somewhere else — through a person.
- Faraday's law of electromagnetic inductionEMF = −N × dΦ/dt
Both conductors pass through one core-balance transformer; only the imbalance produces flux and an induced trip signal.
- Gauss's law for magnetismΦ(B) = 0 (∮ B · dA = 0)
Equal and opposite currents in the same core produce equal and opposite flux which cancels exactly — that null is what makes 30 mA detectable at 63 A.
Each law is stated in full — with its diagram, variables and worked meaning — on the electrical laws page.
How it compares
- MCB vs RCCB
Side by side with MCB (Miniature Circuit Breaker) — specs, variants and which one the job calls for.
Markings
Rating labels show current (e.g., 30mA), voltage (e.g., 230V), and trip sensitivity (often a small 'IΔn' symbol). Test button functionality should be verified periodically.
Standard values
Common trip currents: 10mA (medical), 30mA (general), 40mA (industrial). Standard voltages: 230V, 400V. Breaking capacities: 4.5kA, 6kA, 10kA.
How to choose
1) Select trip current based on application (30mA for general use). 2) Ensure voltage rating matches your supply. 3) Check breaking capacity for your circuit's fault level. 4) Choose Type A for most residential/commercial use, Type B for specialized DC applications.
Pinout & package
Designed for DIN rail or surface mounting. Line (L) and Neutral (N) terminals clearly marked. Load terminals for output connections. No polarity on power terminals but must be correctly wired.
Example circuits
- Main distribution board protection
- Socket outlet in wet areas (bathrooms, kitchens)
- Power tool protection
- Medical equipment safety circuit
- Swimming pool electrical safety
Common failures
Failure to trip when needed (mechanical wear or contamination), nuisance tripping (moisture or dust), internal circuit damage. Test button should be used monthly to verify functionality.
How to test
1) Use the built-in test button (monthly check). 2) For proper testing, use a dedicated RCD tester to verify trip time at rated current. 3) Never bypass or disable a faulty device - replace immediately.
Substitutes
No direct substitutes exist for safety-critical applications. For temporary testing, a portable GFCI/RCD tester can verify circuit protection.