30 mA RCD, type A or AC: reading your panel (Belgium, RGIE)

Quick answer

What to remember about a domestic panel:

• The <strong>circuit breaker</strong> protects the cable against overload and short circuit.
• The <strong>RCD</strong> detects current leaking to earth; the <strong>RCBO</strong> combines both functions on one circuit.
• The RGIE (Book 1) places at least one RCD of <strong>300 mA maximum</strong> at the origin, then at least one of <strong>30 mA maximum</strong> downstream for socket-outlets not reserved for a fixed appliance, lighting, rooms with a bath or shower, and washing machines, tumble dryers and dishwashers.
• In dwellings, RCDs are <strong>at least type A</strong>; a type AC no longer meets that minimum for a new installation.
• A 30 mA RCD may serve <strong>at most 8 final circuits</strong>.
• <strong>Safety:</strong> replacing, adding or modifying a device in the panel is work on a fixed installation, reserved for a qualified electrician.

Circuit breaker, RCD or RCBO: what protects what?

The modular circuit breaker (MCB) trips on overload or short circuit. It protects the cable against overheating. A current through a person is often too small to make it trip.

The RCD (residual-current device, RCCB, described in NBN EN 61008) compares outgoing and returning current. A difference signals leakage to earth: insulation fault, moisture, contact with a person. It then disconnects all live conductors. It does not protect against overload: a plain RCD must be paired with overcurrent protection.

The RCBO (combined RCD and breaker, NBN EN 61009) does both on a single circuit. It is used so that a fault on one circuit does not cut the others.

30 mA, 300 mA and circuits per RCD

Sensitivity (IΔn) is the leakage current at which the device trips. A 30 mA unit reacts to a leakage ten times smaller than a 300 mA one. High sensitivity protects people; the 300 mA protects the whole installation and provides isolation.

The RGIE (Book 1, sub-section 4.2.4.3) places the 300 mA at the origin of the installation. Immediately downstream, at least one high or very high sensitivity RCD takes at minimum the socket-outlets not intended for fixed appliances, the lighting, rooms with a bath or shower, and washing machines, tumble dryers and dishwashers. Fixed appliances such as refrigeration, electric cookers or electric heating may be connected directly behind the main RCD, or on additional RCDs at the origin.

Each 30 mA RCD covers at most 8 final circuits. If the earth electrode resistance exceeds 30 ohms, at least two are needed, with at most sixteen socket-outlets per RCD.

The RGIE also asks that load be distributed so normal appliance leakage currents do not cause nuisance tripping. Each electronic appliance's leakage adds up on one RCD. A tripping RCD can also signal a real fault: do not replace it to make it stop, have an electrician find the cause.

Types AC, A, F, B: which load for which type?

The type says which fault-current forms the RCD still detects correctly. All detect alternating current. The RGIE (sub-section 5.3.5.3) requires RCDs in dwellings to be at least type A.

For ordinary appliances (washing machine, dishwasher, cooker) and for sockets and lighting, the sources consulted state that type A suffices, unless the manufacturer specifies otherwise. For an induction hob, follow the manual. An existing type AC must be assessed by an electrician or accredited body: it is neither automatically acceptable nor automatically to be replaced.

For an EV charging point, the RGIE (7.22.4.1) provides an RCD of 30 mA maximum per charging circuit. Against DC components it provides either an RCD that remains functional in the presence of a DC component (for example type B), or an RCD combined with a residual DC detection device, in the fixed installation or in the charger.

For a heat pump or a PV inverter, the sources set no general 'inverter = type B' rule: the manufacturer's datasheet states the external RCD to use.

• <strong>AC</strong>: sinusoidal alternating current only.
• <strong>A</strong>: alternating and pulsating DC; the domestic minimum.
• <strong>F</strong>: like A, plus some mixed frequencies (single-phase drives), per the manufacturer.
• <strong>B</strong>: also smooth DC fault current.

Curves B and C, ratings and markings

The curve sets the magnetic short-circuit trip threshold. According to manufacturer documentation for domestic breakers (standard IEC 60898-1): curve B trips at 3 to 5 times the rating, curve C at 5 to 10 times. C tolerates inrush currents better; B suits circuits with low short-circuit current.

The rating In is the current the device carries continuously. It must match the cable cross-section and circuit length: an oversized rating no longer protects the cable. That sizing is the electrician's job.

On an RCD, four markings must not be confused:

• <strong>Type</strong> (AC, A, F, B): fault forms detected.
• <strong>IΔn</strong> (30 mA, 300 mA): sensitivity.
• <strong>In</strong> (in A): current the device can carry; at the head of a dwelling, the RGIE asks for at least 40 A.
• <strong>Short-circuit withstand</strong>, poles and test button: the withstand must match the point of installation, and the test button must be reachable without danger of touching live parts.

Selectivity and type S

A 300 mA in front of a 30 mA does not guarantee selectivity: a fault on one circuit may trip the whole panel. A selective (S) or time-delayed upstream RCD lets the downstream 30 mA trip alone.

Do not confuse selectivity (behaviour over time), type (current form detected) and high immunity (resistance to disturbances). A device with enhanced immunity is not automatically selective.

Common mistakes

• Believing the RCD protects against overload, or that the breaker protects against electric shock.
• Confusing sensitivity (mA) and rating (A).
• Leaving a type AC in place without having its situation assessed.
• Putting more than 8 circuits on one 30 mA RCD, or forgetting a relevant circuit (a bathroom towel rail, for example).
• Believing the test button replaces an earth measurement: it only checks the mechanism.
• Replacing a tripping RCD without looking for the cause, or choosing type B 'just in case' without reading the manual.

What to check before buying or quoting, and who does the work

Before choosing a device, go through these points with your electrician:

Work on the fixed installation is reserved for a qualified electrician; this guide describes no operation inside a live panel. According to the FPS Economy, Book 1 also requires an accredited inspection body: a conformity inspection before a new installation is put into use and after any major modification or extension; a periodic inspection visit (every 25 years); and, for installations from before 1 October 1981 without major modification, a visit when power is increased and when the dwelling is sold.

The RGIE is revised: only the version of Book 1 currently in force is authoritative.

• The <strong>type</strong> (at least A) and <strong>sensitivity</strong> (IΔn) suited to the circuit.
• The RCD's <strong>rating In</strong> (at least 40 A at the head) and its <strong>number of poles</strong>.
• The <strong>short-circuit withstand</strong> matching the installation point.
• The <strong>manual of the load</strong> (EV charger, heat pump, inverter, induction hob): it takes precedence for the RCD to use.
• Compatibility with the other devices in the panel and the circuit split (8 maximum per 30 mA).

Frequently asked questions