Choosing the wrong residual current device (RCD) often leaves no room for error: it either trips when it shouldn't, fails to protect as it should, or simply doesn't match the type of load in the installation. If you're looking for how to choose an AC-type RCD, the first thing to understand is that looking only at amperage and price is not enough. You need to consider the type of current detected, sensitivity, number of poles, and the actual use of the line.
The AC-type RCD is still valid in specific installations, but it is no longer the default option for every electrical panel. In traditional homes with simple loads, it might be suitable, whereas in circuits with control electronics, variable speed drives, or equipment with pulsating DC components, it often falls short compared to a Type A. Therefore, it's wise to be precise before buying.
How to choose an AC-type RCD according to the installation
The starting point is simple: an AC type is designed to detect sinusoidal alternating differential currents. This makes it suitable for circuits where the expected leakages are of this type, without significant presence of electronic components that generate more complex waveforms.
In practice, this means an AC RCD can be valid for conventional lighting circuits, general-purpose outlets, or simple resistive loads, provided that the installation design and applicable regulations allow it. If that circuit includes modern washing machines, electronic boards, air conditioning with inverters, chargers, power supplies with rectification, or automation systems, the choice should no longer be made by inertia.
Here's the first real filter: don't just ask which RCD fits in the panel, but what loads that protection feeds. This criterion prevents the most errors.
When an AC type makes sense
It makes sense when the installation is basic, stable, and without equipment that introduces pulsating residual currents or components that complicate detection. In small renovations, equivalent replacements, or very specific secondary panels, it can still be a correct and economical solution.
It is also a common option when the installer needs a specific reference to maintain homogeneity with an existing panel, provided it is still technically compatible. In these cases, cost savings can be reasonable, but they should not outweigh technical suitability.
When to switch to Type A
If there are electronics, the answer is usually clear. Many modern devices generate leakage currents that an AC type cannot detect properly or may affect its behavior. In these environments, a Type A offers more appropriate coverage against AC and pulsating DC currents.
This is not a commercial issue, but a matter of real compatibility with the load. A cheaper RCD that doesn't match the application ends up being expensive in terms of incidents, replacements, or technical review rejections.
Rated current: 25A, 40A, 63A and more
One of the most common mistakes when choosing an AC-type RCD is confusing sensitivity with rated current. The rated current, expressed in amperes, indicates the current the device can continuously withstand without deteriorating. It must be equal to or greater than the expected current in the line or the rating of the associated general miniature circuit breaker, according to the protection scheme.
In residential settings, 40A or 63A RCDs are most common. A 25A might be insufficient in many modern panels, although it could be enough for specific circuits or low-load sub-panels. In light commercial installations or panels with planned expansions, 63A usually provides more leeway.
It's not advisable to oversize without criteria, but undersizing is worse. If the panel is tight or expansions are foreseen, it's better to review the whole system before choosing the minimum reference based on price.
Sensitivity: why 30mA is the usual reference
The sensitivity of the RCD indicates the leakage current at which it will trip. For personal protection, the most common value is 30mA. This is the standard reference in most low-voltage applications for residential and light commercial use.
There are 10mA, 100mA, or 300mA RCDs, but these address different needs. A 10mA offers greater protection in certain environments, though it can cause nuisance tripping if the installation has normal accumulated leakages. A 300mA is more oriented towards fire risk protection or selective schemes, not direct personal protection in final circuits.
If the question is what to install in a home or small premises for general protection, 30mA remains the logical choice in most cases. The important thing is to verify that the entire panel and its branches do not present leakages that push the device to its limit.
2 poles or 4 poles
Another basic criterion when deciding how to choose an AC-type RCD is the number of poles. In single-phase systems, it's normal to work with 2 poles. In three-phase systems, the usual choice is 4 poles. This seems obvious, but quick replacements still see errors from buying a similar reference without checking the actual power supply of the panel.
In a single-phase network, a 2P protects phase and neutral. In a three-phase system with neutral, a 4P controls the three phases and the neutral. If a three-phase panel has inadequate protection due to the number of poles, the protection ceases to function as it should, and the installation remains technically flawed.
It is advisable to check voltage, wiring scheme, and available space on the DIN rail before ordering the reference. For online purchases, this step avoids many returns.
Actual use curve: nuisance tripping and grid quality
It's not all about choosing AC, A, or B. In the field, one of the most annoying incidents is nuisance tripping. This is influenced by the quality of the RCD, the state of the installation, the sum of permanent leakages, and the presence of disturbances.
A standard AC type can work correctly in a simple and clean installation, but become problematic in panels with distributed loads, harmonics, frequent maneuvers, or long lines. In these scenarios, it may be preferable to consider immunized or super-immunized versions if the problem is not the type of residual current but service stability.
This is especially important in commerce, maintenance, and small production facilities, where an unwanted disconnection generates downtime, technical call-outs, and costs. If there's already a history of tripping, it's not advisable to repeat the same reference without diagnosing the cause.
Regulations and technical criteria
Regulations are not to be interpreted by intuition or warehouse custom. Before installing an AC-type RCD, it is necessary to check if the installation, the type of receiver, and the applicable regulations allow this class of protection. In many current applications, the evolution of loads has shifted the use of AC towards more specific scenarios.
Therefore, the correct criterion is not "I've always installed AC" or "it's the cheapest in the catalog." The correct criterion is compatibility with the load, safety of use, and technical compliance. If there is reasonable doubt, it is better to go for a higher class rather than installing a barely adequate protection for a clearly electronic installation.
What to check before buying
Before finalizing the purchase, it's worth taking a minute to check five pieces of information: RCD class, rated current, sensitivity, number of poles, and certification. To this must be added the brand, series, and construction quality if the panel is in a demanding environment or if an exact replacement is sought.
It's also advisable to look at the available space and if a specific solution is needed, such as a self-reclosing or immunized RCD. Protecting a vacation home that is empty for much of the time is not the same as protecting a small business with critical equipment. Context matters.
With a specialized supplier like Bogas Electronics, this point becomes easier because the catalog is usually organized by actual technical typology, not mixed with generic products. For the professional, this saves time and reduces reference errors.
Common mistakes when choosing an AC-type RCD
The first is using it as a universal substitute. It is not. The second is focusing only on amperage and forgetting the type of load. The third, buying 30mA thinking that everything is solved with that, without checking if the RCD class corresponds to the installation.
Another common mistake is installing a correct device on an installation with inherent leakages, shared neutrals, or faulty branches. Then the RCD is blamed, when in reality it is doing its job. Choosing the right device helps, but it doesn't correct defects downstream.
The right decision is not always the cheapest
A properly applied AC-type RCD still makes technical and economic sense. The problem arises when it is used outside its natural scenario. There, it ceases to be an efficient purchase and becomes a source of incidents.
If the installation is simple, the loads are conventional, and regulations permit it, the AC can be a valid, competitive, and easy-to-integrate solution. If there are electronics or a history of tripping, it's advisable to review other classes and versions before repeating a reference out of habit.
The best purchase is not the one that costs the least at the moment, but the one that avoids returning to the panel in two weeks.