RCD, RCCB and RCBO: distinguish the functions
A residual current device (RCD) detects current leakage and disconnects the affected circuit. An RCCB provides residual current protection, while an RCBO also protects against overloads and short circuits. Choosing the right device depends on the connected equipment and the installation requirements - not just the “30 mA” marking.
Compare the devices
| Device | Overload / short circuit | Residual current |
|---|---|---|
| MCB | Yes | No |
| RCCB | No — coordinated overcurrent protection is needed | Yes |
| RCBO | Yes | Yes |
40 A and 30 mA describe different things
How to choose a residual current device (RCD)
A residual current device monitors the difference between the current entering a circuit and the current returning. An imbalance may indicate leakage through damaged insulation or through a person to earth. The device disconnects the supply when its operating conditions are met. It provides additional protection but does not replace a sound electrical installation and protective earthing. Technical reference
RCCB or RCBO?
Our catalogue includes two main options:
The choice depends on the distribution board layout and the protection required for each circuit. RCCB and RCBO explained
Rated current and sensitivity are different
Markings such as 40 A and 30 mA describe different characteristics:
What does the RCD type mean?
The type indicates which residual current waveforms the device detects.
Type Detection
AC Sinusoidal alternating residual current.
A Type AC capabilities, plus pulsating DC residual current.
F Type A capabilities, plus specified mixed-frequency residual currents associated with single-phase inverter loads.
B Includes smooth DC residual current detection.
Choose the type according to the connected equipment and its manufacturer's instructions. RCD type is different from a circuit breaker's B or C tripping curve. RCD types explained
What else should you check?
Compare the number of poles, operating voltage, mounting method and space required in the distribution board. For an RCBO, also check the tripping curve and breaking capacity. For an RCCB, verify coordination with the short-circuit protective device using the manufacturer's documentation. Protection coordination
Final selection, installation and testing should be carried out by a qualified electrician according to the specific installation. If you already have the required specifications, the Electromateriali.com team can help you find a model and confirm availability.
Choose the type for the residual waveform
| Type | Main distinction |
|---|---|
| AC | Sinusoidal alternating residual current |
| A | Also pulsating direct residual current |
| F | Additional composite frequencies for certain single-phase inverter loads |
| B | Includes smooth direct residual current within manufacturer-specified conditions |
Practical example: circuit-level protection
With several circuits behind one RCCB, a fault on one can disconnect them all. Individual RCBOs can limit the interruption to the affected circuit when the overall arrangement is correctly installed and coordinated. This can aid fault location but does not eliminate the need to check selectivity.
For an EV charger, photovoltaic inverter or heat pump, read the specific equipment requirements. Do not select the type from the appliance name alone. Type B for an RCD is unrelated to curve B for a circuit breaker.
Before purchase
- Functions: RCCB or RCBO; for RCBO also current, curve and breaking capacity.
- Sensitivity IΔn and AC/A/F/B type for the load and design.
- Poles, voltage, panel space and compatible busbars.
- Coordination with upstream devices and accumulated normal leakage.
- The specific model's TEST-button instructions and checking interval.
Common questions
Does TEST prove the whole installation is safe? No. It exercises the manufacturer's test function, not PE continuity or every condition needed for safety.
Why does it trip without an obvious fault? Possible causes include accumulated appliance leakage, insulation faults or incorrect connections. Measurements are needed; never bypass the protection.
Installation and verification
An electrician must verify the earthing arrangement, neutral separation, coordination and protective operation. Do not treat adding an RCD as a standalone remedy for an unverified old installation.