Residual current device

The residual current device (RCD) is a modular protective device designed to detect earth leakage currents resulting from an insulation fault. It automatically cuts off the electrical supply as soon as the residual current exceeds the set sensitivity threshold. Standard ratings cover 30 mA for personal protection and 300 mA or 1 A for fire protection, with two-pole or four-pole versions depending on the type of network to be protected.

Function of the residual current device and distinction from the circuit breaker

Specific protection against insulation faults

Our installation experience confirms that the RCD reacts exclusively to leakage currents to earth. It does not protect against overloads or short circuits, unlike the circuit breaker, which handles these functions. We systematically recommend combining both devices at the head of the installation for complete protection of people and property.

Detection principle and sensitivity thresholds

The device continuously measures the imbalance between the phase current and the neutral current. As soon as part of the current leaks to earth, the RCD trips within a few milliseconds. The 30 mA threshold is the reference for protecting people against direct or indirect electric shock.

Types of leakage current and choosing between type AC, A or F

Type AC for standard resistive and inductive loads

Type AC detects alternating sinusoidal leakage currents. Feedback from installers confirms that it suits traditional installations mainly comprising resistive, inductive loads or standard asynchronous motors.

Type A for electronic loads and rectifiers

Type A also detects pulsating DC leakage currents from modern electronic equipment. In the field, we find that washing machines, LED drivers and rectifier-based equipment absolutely require this type to guarantee reliable detection.

Type F for variable-speed drives and inverters

Type F detects high-frequency-component leakage currents generated by variable-speed drives and inverters. Our standard practice favours this type in industrial installations containing power electronics.

Compliance standards and panel mounting

IEC 61008 certification and application of NF C 15-100

Residual current devices comply with the IEC 61008 standard, which defines operating rules, type tests and performance criteria. In France, their installation is governed by NF C 15-100, which specifies their location, sensitivity and coordination with other protective devices.

Integration on DIN rail in modular panels

The polyamide housing fixes onto a standard DIN rail in enclosures and electrical panels. Our commissioning tests show that this modular mounting allows fast installation and easier maintenance in residential, tertiary and industrial panels.

Typical applications and positioning within the installation

Protection at the head of the general installation

We frequently see a residual current device positioned upstream of the sub-distribution board to protect the whole installation. This centralised configuration offers overall protection with a single head-of-installation device.

Protection per dedicated circuit according to installation zones

Per-circuit protection allows a specific RCD to be associated with each sensitive line, such as wet rooms or outdoor circuits. Our installation feedback shows that this approach limits the spread of tripping in the event of a fault and makes diagnosis easier.

Frequently asked questions

Can a residual current device replace a circuit breaker?

No, the residual current device does not replace the circuit breaker, as it provides no protection against overloads or short circuits. The two devices are complementary and must be installed in series for complete protection in line with NF C 15-100.

How should you choose between 30 mA, 300 mA and 1 A sensitivity?

30 mA sensitivity is mandatory for personal protection in residential premises and areas at risk of electric shock. The 300 mA or 1 A thresholds relate to fire protection in unoccupied premises or outgoing circuits for large consumers, where a high leakage current could cause overheating.

What is the difference between a residual current device and a residual current circuit breaker?

The residual current device provides only residual-current protection, whereas the residual current circuit breaker combines residual-current protection with overload and short-circuit protection in a single housing. The choice depends on the protection strategy adopted by the design office.

Why is a type A device necessary with LED luminaires?

The electronic power supplies of LED luminaires generate pulsating DC-component leakage currents that type AC does not detect. Type A guarantees tripping in the presence of these specific faults, in line with the standard's requirements for circuits containing electronics.