In a home, choosing the wrong residual current device (RCD) often doesn't show its face on the day it's installed. The problem appears later: nuisance tripping, incompatibility with certain equipment, or protection that doesn't match the actual use of the installation. That's why, when someone asks what RCD a home needs, the technical answer is not just one reference, but a correct combination of sensitivity, rating, number of poles, and type of RCD.
In a residential environment, the usual starting point is still a 30 mA residual current device for personal protection. This sensitivity is standard in most domestic switchboards because it can detect dangerous earth leakages before they reach hazardous levels. However, from there, several things change: a basic single-phase home is not the same as a home with aerothermal heating, an induction hob, an electric vehicle charger, or electronic equipment that generates more complex residual current components.
What RCD a home needs according to the installation
If we are talking about a conventional single-phase home in Spain, the most common is to work with a 2-pole, 30 mA RCD, and a rating in accordance with the assigned intensity of the main switchboard line, usually 25 A, 40 A, or 63 A depending on design and load forecast. The 30 mA value protects against indirect contact. The amperage value does not mark the trip sensitivity, but the current that the device can continuously withstand.
Here appears a fairly common mistake: thinking that the more amperage the RCD has, the better. Not necessarily. It must be coordinated with the installation and with the main circuit breaker. Oversizing without criteria does not provide a real improvement in protection and can complicate selectivity or make the solution more expensive unnecessarily.
In a three-phase home, the criterion changes to the number of poles. In that case, the usual is a four-pole or 4-pole RCD. The 30 mA sensitivity is still the most used for personal protection, but the type and rating must be analyzed based on the connected loads.
Not all domestic RCDs are the same
The question of what RCD a home needs is often asked as if it were enough to choose between 25 A or 40 A, but today that is not enough. In modern residential installations, the class of the RCD is decisive.
AC type RCD
The AC type detects sinusoidal alternating residual currents. For years it has been massively installed in homes, especially in simple switchboards with traditional loads. The problem is that a modern home rarely maintains only loads of this type. Sources with electronics, appliances with variation, LED lighting, inverter air conditioning, or certain chargers may make it advisable to move up to a higher technical level.
Type A RCD
The Type A detects alternating residual currents and also pulsating direct current components. In modern homes, in many cases, it is the most sensible option as a technical minimum. If there is a washing machine, ceramic hob or induction hob, electronic oven, inverter air conditioning or equipment with power electronics, Type A offers a more suitable response than an AC.
Therefore, for many installers, the correct question is no longer whether to put AC or A out of habit, but whether the residential switchboard still justifies an AC. In new construction, comprehensive renovation, or switchboard upgrade, Type A is usually the most coherent choice.
Super-immunized or SI RCDs
When there are nuisance trips, there isn't always a real dangerous leak. Sometimes the problem comes from transient disturbances, harmonics, or peaks generated by electronic equipment. In these cases, a super-immunized or SI RCD can prevent unwanted trips without sacrificing protection.
This is seen a lot in homes with a lot of electronics, teleworking, home automation, sensitive refrigerators, pumps, inverter air conditioning, or small automation systems. It is not mandatory in all homes, but it is highly recommended when service continuity matters or when annoying outages have already been detected without a clear cause of fault.
Type F and Type B in homes
Type F makes sense in specific applications with single-phase drives or certain inverter loads where a Type A may fall short in performance. Type B already enters more specific scenarios, such as certain charging systems, photovoltaics, or equipment with more demanding DC residual current components.
In a standard home, it is not always necessary to go to an F or a B. But if the installation incorporates specific equipment with requirements defined by the manufacturer or by applicable regulations, then improvisation is not an option. There, selection must be made by technical compatibility, not by price or custom.
Sensitivity: why 30 mA is the usual reference
The most common sensitivity in homes is 30 mA. This value is aimed at protecting people and is the standard in the vast majority of domestic switchboards. A 300 mA RCD, for example, may make sense in other environments for fire protection or upstream in certain configurations, but it does not replace the function of a 30 mA RCD in circuits for habitual domestic use.
It is also worth avoiding a common misconception: a more sensitive RCD does not always mean a better installation. If sensitivity is reduced without criteria or without studying permanent leaks in the installation, the risk of nuisance tripping can increase. In homes, 30 mA remains the correct balance point in most cases.
Amperage: 25 A, 40 A or 63 A
The rating of the RCD must be chosen based on the expected current and the associated protection. In residential switchboards, 40 A is one of the most common formats because it fits well in many typical single-phase homes. 25 A is also used in smaller installations and 63 A when the installation or load forecast requires it.
It's not about choosing the highest "just in case." If the switchboard is calculated for a certain current, the RCD must accompany that design. The correct criterion is technical: assigned current, switchboard diagram, upstream protections, and type of supply.
What RCD a home needs with modern equipment
When the home incorporates aerothermal heating, inverter air conditioning, an electric vehicle charger, an induction hob, home automation, or a high concentration of electronics, it is advisable to refine the choice further. In such cases, a Type A is often the reasonable minimum, and a Type A-SI or super-immunized can make a difference in stability.
In homes where an RCD trip leaves the refrigerator, connectivity, alarm, or critical equipment without service, continuity is no longer a minor detail. In this context, auto-reclosing RCDs also enter the conversation. They do not replace the analysis of the cause of the trip, but in certain residential installations they provide a clear advantage: automatic restoration of the supply after a punctual incident verified by the equipment itself.
However, not every home needs auto-reclosing. If the installation has a real fault, an auto-reclosing device is not the way to cover up the problem. It makes sense when continuity is sought against sporadic trips and when the installation environment technically allows it.
Common mistakes when choosing a home RCD
The first is to focus only on price. In electrical protection, a small cost difference between a basic AC and an A or an SI can prevent recurring incidents, call-outs, and complaints.
The second is to ignore the class of the RCD. Today, many homes have loads that no longer fit well with an old solution designed only for resistive loads or very simple motors.
The third is not to review the number of poles, the rating, or the compatibility with the rest of the switchboard. A correct RCD is not chosen in isolation. It is integrated into a complete protection solution.
And the fourth is to think that all trips are the fault of the RCD. Many times the device is doing exactly its job. The origin can be in derivations, accumulated leaks, humidity, crossed neutrals, or electronics that require a more appropriate typology.
So, what RCD does a home need?
In most current single-phase homes, the practical answer is usually this: a 2-pole, 30 mA RCD with a rating adapted to the switchboard, usually 40 A in many cases, with a preference for Type A over Type AC if there are common electronic loads, which are almost the norm today. If there is also a history of nuisance tripping or an installation with a high electronic load, a super-immunized one can be a much more cost-effective decision than continuing to replace equipment without solving the functional origin.
In three-phase homes, the approach usually changes to 4 poles, maintaining the 30 mA sensitivity and adjusting the class and rating according to real loads. If specific equipment appears, such as electric vehicle charging, drives, or special systems, the choice must be made according to the technical specification of the use.
For a professional, the key is not just to ask what RCD a home needs, but what RCD that specific home needs. That's where you really get it right: analyzing the supply, diagram, loads, service continuity, and expected type of leakage. If the goal is to install protection that doesn't cause problems either at delivery or months later, it is advisable to choose by actual application and not by generic reference. This fine-tuning is what avoids apparent faults, unnecessary visits, and switchboards that become a source of incidents.