What an RCD Is
An RCD (residual current device, УЗО) is a device that monitors the difference in current between the phase and neutral conductors. In the event of a current leakage to earth (for example, when a person touches a bare wire or the insulation is damaged), the RCD instantly disconnects the circuit.
Important: an RCD does not protect against overload or short circuit. That is why a circuit breaker must always be installed ahead of the RCD.
What an RCBO (AVDT) Is
A residual-current circuit breaker with overcurrent protection (RCBO, AVDT) is a combined device that integrates the functions of a circuit breaker and an RCD in a single housing. It protects against overload, short circuit and current leakage all at once.
Comparison of Characteristics
| Parameter | RCD + circuit breaker | RCBO (AVDT) |
|---|---|---|
| Overload protection | Circuit breaker | Built in |
| Short-circuit protection | Circuit breaker | Built in |
| Leakage protection | RCD | Built in |
| Space in the panel | 4 modules (2+2) | 2 modules |
| Cost | Lower overall | Higher |
| Diagnostics on tripping | You can see what tripped | Cause not always clear |
| Replacement on failure | One device is replaced | The whole unit is replaced |
Leakage Current: 10 mA or 30 mA
- 10 mA — for wet rooms (bathroom, sauna) and dedicated circuits for a washing/dishwashing machine
- 30 mA — the standard rating for socket groups and general protection per the PUE (clause 7.1.79)
- 100–300 mA — a fire-protection RCD at the incomer, protecting against fire caused by leakage
RCD Type: AC or A
- Type AC — responds to sinusoidal leakage current. The most common and inexpensive.
- Type A — responds to both sinusoidal and pulsating DC leakage current. Recommended for circuits with washing machines, frequency converters and switch-mode power supplies.
When to Install Which
RCD + circuit breaker:
- When a single RCD protects several circuits (cost saving)
- When diagnostics matter: the toggle of the breaker or the RCD shows exactly what tripped
- In panels with a large number of circuits
RCBO:
- When there is little space in the panel
- For individual critical circuits (washing machine, water heater)
- During a retrofit, when protection needs to be added without replacing the panel
Regulatory Requirements
According to the PUE (7th edition, clauses 7.1.71–7.1.85), installing an RCD with a 30 mA leakage current is mandatory for socket groups in residential premises. At the incomer, installing a fire-protection RCD of 100–300 mA is recommended.
You can select RCDs and RCBOs in our catalog.