A residual current device (RCD) that trips without a real leakage current does not offer better protection. For installation alone, it generates warnings, wastes time, and in many cases, ends up concealing the underlying problem. This guide to immunized RCDs is intended for those who need to make the right choice the first time: installers, maintainers, and technical buyers working with residential, commercial, or small industrial panels.
Immunized RCDs are used when there are transient disturbances, harmonics, maneuvers, or electronic equipment that make the RCD operate in less clean conditions than those of a conventional installation. They do not replace the panel design criteria or correct wiring errors, but they do help prevent nuisance tripping when the installation requires it.
What is an immunized RCD?
An immunized RCD is a residual current circuit breaker designed to offer greater resistance to unwanted tripping caused by disturbances in the network or loads. In practice, it maintains sensitivity to real leakage currents but improves its performance against peaks, transients, and certain components that can confuse a standard RCD.
This is especially useful in installations with power electronics, LED lighting, variable frequency drives, HVAC, switched-mode power supplies, chargers, UPS, or frequent switching. In these environments, a conventional RCD can trip without a dangerous permanent leakage current. The result is known to any technician: calls, shutdowns, and unnecessary replacements.
When talking about immunized RCDs, it is also common to find commercial names such as SI, superimmunized, or high immunity. It is always advisable to review the specific technical data sheet, as not all brands use the same nomenclature or the same level of performance against disturbances.
When is it advisable to install an immunized RCD?
It is not necessary to install an immunized RCD in every panel. There are many simple residential cases where a suitable AC or A class RCD, well-selected and well-wired, works without incidents. The immunized RCD makes sense when there is a real problem of electrical compatibility or a high probability of nuisance tripping.
It usually fits well in homes with a lot of electronic load, panels with computer or telecommunications circuits, commercial premises with intensive LED lighting, installations with inverter air conditioning, pumps with electronics, automatic doors, or small industrial processes. It is also a common solution at the head of a panel where an unwanted disconnection affects several downstream circuits.
There is an important nuance: if the RCD trips due to a real leakage current, neutral mix-ups, insulation fault, or poor sectorization, installing an immunized RCD does not fix the cause. In these cases, it only delays the diagnosis and complicates subsequent intervention.
Immunized RCD guide by class
The part that generates the most doubts is not whether the equipment is immunized, but what RCD class the load needs. That's where real compatibility is defined.
AC Class
AC class detects sinusoidal alternating differential currents. Today it is still present in simple installations, but it falls short in many environments with electronics. If there is equipment with rectification or pulsating current components, it is advisable to consider a higher class. An immunized AC can improve performance against disturbances, but it does not change the inherent limitations of its class.
A Class
A class detects alternating currents and pulsating currents with a DC component. For many current installations, it is a reasonable starting point. Modern appliances, electronic power supplies, regulated lighting, or light air conditioning usually justify its use. If there is also a history of nuisance tripping, an immunized A-type or A-SI is usually a more coherent choice than installing another AC.
F Class
F class is oriented to single-phase loads with variable frequency drives and equipment with more complex waveforms. It is common to consider it in pumps, inverter air conditioning, compressors, or certain motors with electronic control. When this type of load works continuously, an immunized F can provide additional stability against annoying tripping.
B Class
B class is reserved for more demanding applications, where smooth continuous or variable frequency differential currents may appear. It is common in electric vehicle chargers, three-phase drives, photovoltaics, or certain industrial processes. Here it is not about improving comfort, but about installing the correct differential technology. If the application requires B, an immunized A is not a valid alternative.
How to choose the correct immunized RCD
Choosing correctly involves cross-referencing several technical data. The first is the class, because it determines what type of differential current it can detect. The second is the sensitivity, usually 30 mA for personal protection in final circuits, although in certain applications, other values are used depending on the protection scheme, selectivity, or function.
Then you have to check the nominal current. A 25A, 40A, 63A or higher is not chosen out of habit, but based on the expected current, the associated protection, and the panel configuration. Installing an undersized caliber can generate overheating or tripping due to overall overload, even if the problem seems to be differential.
The number of poles also matters. In single-phase, 2P is common. In three-phase, 4P. It seems obvious, but in panel expansions or quick replacements, this is where most compatibility errors are carried over.
Selectivity deserves attention. In panels with several RCDs, it is advisable to study staggering and circuit distribution so that an incident does not leave the entire installation out of service. An immunized RCD can coexist with selective RCDs or with reclosing solutions, but it does not replace good protection architecture.
Immunized RCD and auto-reclosing: not the same thing
Many buyers confuse both concepts. An immunized RCD is designed to better withstand disturbances and prevent unwanted tripping. An auto-reclosing RCD or an automatic reclosing system acts after tripping, restoring service if the fault condition has disappeared and the equipment's logic allows it.
They can be combined, and in fact, in certain installations, it is a very practical solution. For example, in unattended locations, second homes, telecommunications, pumping, or services that should not be de-energized by a momentary transient. But the type of load, coordination with circuit breakers, and safety conditions must be thoroughly reviewed before defining such a solution.
Common mistakes when ordering or replacing equipment
The most common mistake is to ask for “an immunized one” without specifying the class, poles, amperage, or sensitivity. With that level of information, it is easy to receive equipment that does not fit the application. The second mistake is to replace an AC with another AC when the installation has already changed and now has much more electronics than years ago.
Another frequent mistake is to think that all nuisance tripping comes from the RCD. Sometimes the origin is in the sum of leakage currents from several receivers, in neutrals shared between lines protected by different RCDs, in EMC filters, in humidity, or in poor panel sectorization. In these situations, the immunized RCD may improve something, but it does not solve the design defect.
It is also advisable to verify certifications, CE marking, and clear technical documentation. In electrical protection, it is not enough for the format and price to fit. The reference must respond consistently to the type of installation.
What to check before buying
If you want to get it right without detours, there are four pieces of information you should be clear about before ordering the material: RCD class, nominal current, sensitivity, and number of poles. Add to that the real context of the load. Protecting a home with home electronics is not the same as a small workshop with variable frequency drives or a commercial installation with LED, HVAC, and computers running at the same time.
When the panel already shows tripping, it is useful to review the history. If the problem appears when starting air conditioning, connecting lighting, after storms, or network maneuvers, the pattern helps a lot to choose between A-SI, F-SI, or a solution of another class. If the tripping is random and persistent, before changing just for the sake of changing, it is advisable to measure, sectorize, and check for real leakage currents.
In a specialized catalog like Bogas Electronics, where specific references of AC, A, F, and B, immunized versions, 2P, 4P, and auto-reclosing options are handled, this precision is what avoids returns, incompatibilities, and downtime on site or during maintenance.
The immunized RCD guide for a realistic decision
It is not always necessary to go for the most advanced or the cheapest equipment. The right decision is usually at the point where the RCD class responds to the load, the immunity reduces unwanted tripping, and the price still makes sense for the installation. That's where the technical balance lies.
If the load is conventional and the panel is well designed, an adequate standard RCD may be sufficient. If the installation has electronics, maneuvers, or a clear history of nuisance tripping, the immunized RCD ceases to be an extra and becomes a logical choice. Choosing correctly from the right technical reference usually costs less than revisiting the same fault twice.