If you've arrived with the question of which type A differential I need, you probably don't lack general theory: you need to find the correct reference. And that's where errors usually occur. It's not enough for it to be "type A." You need to cross-reference class, current rating, sensitivity, number of poles, and behavior against nuisance tripping.
The type A residual current device (RCD) is designed to detect sinusoidal alternating residual currents and pulsating residual currents with a DC component. This is why it is no longer a minority option in current installations. As soon as electronic loads, single-phase rectifiers, or equipment with variation and control appear, switching from AC to A ceases to be an optional improvement and becomes a logical choice.
Which type A RCD do I need according to the installation?
The correct question is not just which type A RCD I need, but for which circuit, with which loads, and under what service conditions. In a basic home, it can cover lines with appliances, consumer electronics, lighting with drivers, and equipment with switched-mode power supplies. In a small commercial premises or light tertiary sector, it is also usually the reasonable option when there is air conditioning, control electronics, computer equipment, or light machinery with electronic components.
The first filter is functional compatibility. If the circuit feeds loads that can generate pulsating residual currents, type A is the recommended technical minimum. This occurs quite frequently with washing machines, induction hobs, modern ovens, chargers, power supplies, simple variable speed drives, and many pieces of equipment that are already part of the daily life of any renovated or new installation.
However, type A does not automatically mean that any unit will do. A 25A 30mA 2P and a 63A 30mA 4P are both type A, but they are designed for very different scenarios. The real choice begins when you get down to the specification.
Amperage, sensitivity, and poles: what defines the reference
The nominal current rating, expressed in amperes, must be consistent with the current of the protected circuit or line and with the upstream or downstream miniature circuit breaker (MCB), depending on the diagram. In homes and small tertiary sectors, 25A, 40A, and 63A are common. If the RCD is going to protect a set of circuits from the main panel, 40A or 63A often appear. If it is dedicated to a specific line, the calculation changes.
The most common sensitivity is 30 mA because it is standard for personal protection. It is the most sought-after reference for residential panels, offices, small businesses, or terminal circuits. Higher sensitivities, such as 100 mA or 300 mA, respond to other criteria, more linked to selectivity or fire risk protection, and do not simply replace 30 mA when additional personal protection is required.
The number of poles also immediately rules out many options. In normal single-phase systems, 2 poles are typical. In three-phase systems or panels with 3F+N distribution, the correct equipment is usually 4 poles. It seems obvious, but in quick purchases, it is one of the most common mistakes: getting the class and sensitivity right, but not the pole configuration.
When a standard type A is not enough
Not all RCD trips are due to a real dangerous fault. In installations with a lot of electrical noise, harmonics, switching operations, EMC filtering, or permanently connected electronic equipment, a standard type A RCD can cause nuisance tripping. And that's where it's advisable to consider immunized or super-immunized versions, depending on the manufacturer and range.
This is especially important in cold rooms, offices with a lot of electronics, small telecommunications panels, automation, air conditioning, and premises where an unplanned disconnection causes operational incidents. Technically, the device is still type A, but with a response better prepared for transient disturbances and high-frequency leakage currents that, without being a clear fault, end up causing annoying trips.
If the installation already experiences false trips, replacing an AC with an A may not be enough. In that case, the criterion should not only be the RCD class but also its immunity level.
Which type A RCD do I need in a home?
In modern homes, type A makes sense in more circuits than was assumed a few years ago. Kitchen, laundry room, air conditioning, and any line with integrated electronics are clear candidates. Appliances with electronic control, chargers, LED power supplies, and modern hobs and ovens often make AC far too short in many real cases.
If it is a standard single-phase domestic panel, a common configuration is 2P, 40A, and 30mA, although this should not be taken for granted without checking the planned current and the panel diagram. In large homes, with high electrification or grouping of several lines, it may be more reasonable to go up to 63A. If the environment presents sporadic trips without a clear fault, considering a type A SI can save many after-sales incidents.
In partial renovations, it is also advisable to look at the whole picture. There is no point in installing an RCD suitable for the new kitchen line if the rest of the panel maintains a configuration that compromises selectivity or generates excessively high accumulated leakage currents.
In commercial premises and light tertiary sector
Here the analysis changes because electronics are usually more constant and denser. Cash registers, routers, UPS, air conditioning, lighting with drivers, signage, small motors, and control equipment increase the probability of non-sinusoidal residual currents and unwanted tripping.
Therefore, when someone asks which type A RCD I need for a premises, the answer is rarely just "a 30mA one." You have to look at the sum of loads, the distribution of circuits, and the required service continuity. In many panels of this type, an immunized type A RCD fits better than a standard model, even if the price is slightly higher. It is cheaper than an apparent fault that is actually a repeated nuisance trip.
In three-phase systems, 4P is the natural option. And if there is a loaded neutral, distributed electronics, or unbalanced loads, there is even more reason to carefully review the amperage sizing and not buy out of habit.
What should not be confused with a type A
A common mistake is to think that type A is suitable for any "modern" load. Not always. When more demanding frequency converters, specific chargers, photovoltaics, certain pumps, or equipment capable of generating smooth continuous residual currents come into play, it may be necessary to switch to type F or type B, depending on the application.
Type F goes a step further in certain single-phase loads with frequency variation. Type B already covers scenarios where a type A does not offer adequate detection. It's not about over-sizing systematically, but about not falling short by oversimplifying. The correct RCD is the one that corresponds to the expected leakage of the actual equipment, not the one that "is normally installed."
How to get it right without buying twice
If you want to avoid returns, incompatibilities, or a panel that keeps failing, you should check five pieces of information before ordering the unit: network type, number of poles, nominal current, sensitivity, and nature of the load. If the installation also has a history of tripping, add a sixth piece of information: the need for immunization or auto-reclosing.
An auto-reclosing device does not compensate for a poor choice of class. It is useful when continuity of supply is critical and transient trips are controlled, but it must be installed judiciously. Reclosing a poorly diagnosed installation does not solve the underlying problem.
For many professionals, the correct reference ends up being a very specific combination: type A, 30mA, 2P or 4P, with the amperage adjusted to the panel and, when the environment demands it, an SI or auto-reclosing version. This level of precision is what prevents errors. In a specialized technical catalog like Bogas Electronics', this search by specification makes more sense than sticking to the general label of "type A RCD."
The practical decision
If the installation includes common electronics and you are not facing a special load that requires F or B, type A is usually the correct starting point. From there, the selection is refined with 30mA or the sensitivity required by the project, 2P or 4P depending on the network, and 25A, 40A, or 63A depending on the line and panel configuration.
When there is real doubt, it is almost never about the letter A. It is about everything else: whether you need immunized, whether the panel is single-phase or three-phase, whether you are protecting a circuit or a main supply, and whether the electronic loads will work stably or with a lot of background noise.
Choosing an RCD well is not a mystery, but it does require technical detail. And in electrical protection, detail is what separates a quick purchase from a correct reference that doesn't cause problems the following week.