The super-immune RCD (also called a super-immunised RCCB) is a type of residual-current device with enhanced filtering that prevents nuisance tripping caused by harmonics and other electrical disturbances. In any installation, the RCD protects people and equipment against earth-leakage currents by disconnecting the circuit as soon as it detects a dangerous imbalance.
In environments with lots of electronics, however, small high-frequency leakages and brief transients can make a standard RCD trip when there’s no actual fault. That’s where a super-immune RCD comes in: it provides the same high-sensitivity protection (e.g., 30 mA) while remaining immune to the interference that typically causes unwanted trips.
What exactly is a super-immune RCD?
A super-immune RCD is, essentially, a Class A RCD (typical 30 mA threshold) that integrates special electronic filters to distinguish a real earth leakage from a fleeting disturbance. Like any RCD, it monitors the current entering on the live and returning on the neutral; if the difference exceeds the set threshold, it opens the circuit to prevent electric shock or fire. The difference is that the super-immune version is engineered not to trip under conditions that would make a standard device operate even when no fault exists.
They are called “super-immune” because they show superior immunity to the usual causes of false trips. Internally they include high-frequency filters and circuitry that ignore harmonics and short transients. In practical terms, a super-immune RCD tells a real threat from a false alarm: it “looks through” tiny, short-lived leakages that are normal in the presence of electronic equipment, yet still reacts immediately if there is a genuine earth fault.
Technically, most super-immune devices are Class A (they detect sinusoidal AC and pulsating DC). “Super-immune” is not a new standard class; it is a design improvement on Class A with anti-harmonic filtering. Many manufacturers mark them “SI”.
Benefits and how it avoids trips due to harmonics
The main advantage is resistance to nuisance trips caused by harmonics and other network disturbances. In modern installations, many devices (computers, switch-mode supplies, electronic controls, LED lighting, variable-speed drives, etc.) generate small high-frequency leakages or brief inrush peaks. A conventional RCD may interpret the sum of those as a fault and trip even when none exists. A super-immune model incorporates “anti-harmonic” filtering to tell the difference.
How does it avoid trips from harmonics? Thanks to its high-frequency filtering, the super-immune unit does not react to leakages dominated by harmonic content (frequencies above 50/60 Hz) or to extremely brief transients. For example, with LED or fluorescent lighting that includes EMI filters, it is normal to have small permanent leakages per luminaire. If many loads start at once, a momentary peak might make a standard RCD trip. The super-immune device filters that peak: it only trips if the leakage persists long enough and has the waveform signature of a real fault. In short, it blocks false tripping and improves supply continuity.
All of this is achieved without sacrificing safety: if there is a true earth leakage (e.g., a person touches an energised part, or damaged insulation contacts metalwork), the super-immune RCD will operate as fast as a regular 30 mA device. The result is clear benefits:
- Fewer unnecessary outages: Avoids power cuts when there’s no real problem—key in offices, shops, home automation or IT rooms where a nuisance trip means lost data or downtime.
- Greater service life and trust: Less needless tripping reduces mechanical/electrical wear and gives users more confidence in the installation.
- Targeted protection for harmonic-rich environments: Ideal where harmonic distortion and electronic loads are plentiful (drives, converters, LED drivers, SMPS, etc.).
Typical applications: when should you use a super-immune RCD?
- IT and electronics-heavy spaces: Offices, server rooms, data closets, or modern homes packed with electronics (computers, TVs, chargers, consoles). Super-immune RCDs help avoid trips when multiple supplies power up together.
- Electronic lighting systems: Sites with extensive LED or fluorescent lighting (with electronic ballasts) and dimming. Such loads introduce harmonics and HF leakages that can trip ordinary devices. A super-immune RCD mitigates that risk.
- Motors with drives and industrial equipment: VSD-driven machinery, lifts, HVAC inverters, pumps with speed control. These generate high-frequency components and transients at start/stop. Super-immune RCDs prevent nuisance shutdowns.
- Installations where the RCD “trips for no obvious reason”: Repeated trips with no identifiable fault suggest transient or harmonic leakage—an indicator to upgrade to super-immune.
- High continuity of service: Hospitals/labs or second homes where an accidental trip could leave the site without power for hours or days. Super-immune significantly reduces spurious disconnections.
Note: You don’t have to use super-immune on every circuit. For simple loads, a standard Class AC or Class A may suffice. Given the slightly higher cost, deploy super-immune models strategically on the most electrically noisy boards or lines.
Comparison of RCD types: AC, A, Super-Immune and B
| RCD type | Leakage it detects | Characteristics & typical uses |
|---|---|---|
| Class AC | Only sinusoidal AC (50/60 Hz). | Most basic. Suitable for resistive/inductive loads with little electronics. Does not detect DC components and can nuisance-trip with modern electronics. |
| Class A | Sinusoidal AC and pulsating DC (e.g., single-phase rectifiers). | Standard choice for typical appliances and electronic loads. Better safety than AC type, but can still react to high-frequency harmonics if many devices are present. |
| Super-immune (Class A “SI”) | Same as Class A, with extra immunity to HF transients and momentary peaks. | Best for environments rich in electronics and electrical noise. Minimises nuisance tripping while maintaining full 30 mA personal protection. |
| Class B | AC, pulsating DC and smooth DC (rectified, filtered). | Special devices for applications with possible smooth DC leakage (EV chargers, some PV inverters, specific industrial gear). Much costlier; use only when the load requires it. |
As the table shows, the super-immune sits within the Class A family, adding robustness against interference. Don’t confuse it with Class B, which is reserved for detecting smooth DC leakages (e.g., >6 mA DC) typical of EV charging or specific inverter topologies.
Installation, regulations and final considerations
Installing a super-immune RCD is just like installing any other RCD. It comes in modular format for 35 mm DIN-rail mounting in the distribution board, typically in 2 modules for 1P+N (single-phase) or 4 modules for three-phase. Replacing an existing device is straightforward: choose the same rated current (25 A, 40 A, 63 A) and sensitivity (usually 30 mA for personal protection).
From a standards perspective, super-immune RCDs comply with IEC/EN 61008-1 (general RCD standard) and IEC 61543 (EMC/immunity for RCDs). They bear CE/UKCA marking and are fully compatible with national low-voltage regulations. Remember that an RCD does not protect against overloads or short circuits; that’s the role of thermal-magnetic circuit breakers or fuses. In a typical board, MCBs protect each circuit from overcurrent while the RCD supervises multiple circuits for earth leakage. Swapping a standard RCD for a super-immune one preserves this coordination—you simply gain stability by avoiding spurious trips.
Maintenance is identical to any RCD: use the test button periodically. If your installation has several RCDs, you can fit super-immune models only on critical or problematic branches and keep standard ones elsewhere. Many professionals deploy at least one super-immune as a head device or on boards feeding heavy electronics.
Also note there are auto-reclosing RCDs that restore power after a trip once they verify the fault has cleared. Don’t confuse these with super-immune devices: a super-immune RCD prevents nuisance tripping in the first place; an auto-reclosing RCD restores supply after tripping, which can be useful in combination to maximise continuity.
Conclusion
A super-immune RCD is highly recommended in today’s electronics-rich homes and businesses. It delivers the sensitive electrical protection we need (instant reaction to dangerous leakages) while avoiding the annoyance and cost of unwanted trips caused by harmonics or transients. Result: more stable, safer installations that protect both people and equipment with a superior level of reliability.
If your RCD trips frequently with no clear cause—or you’re planning a project with lots of electronic loads—consider installing a super-immune model. In the Solera RCD range you’ll find different options, including the RCBSI2P40/30 (2-pole, 40 A, 30 mA) among others. With the right choice, you’ll achieve robust earth-leakage protection without sacrificing sensitivity—or continuity of supply.
For related topics, explore our guides on overvoltages, IP protection and best practices in electrical installations on Solera’s news blog.