A solar installation may be well-sized in terms of panels, inverter, and circuit breakers, yet still present problems due to a poor choice of residual current device (RCD) for the photovoltaic system. It usually doesn't fail due to power. It fails due to incompatibility between the type of residual current the inverter can generate, the sensitivity of the equipment, and the actual behavior of the installation when it goes into operation.
In photovoltaics, it is not advisable to choose the RCD as if it were a standard domestic circuit. The inverter, EMC filters, capacitive leaks from the cables, and the grid connection configuration itself significantly change the scenario. Therefore, if an unsuitable type is installed, the usual outcome is unwanted trips or, worse still, a protection that does not respond as it should to a specific leakage current.
What an RCD for a photovoltaic installation should cover
The main criterion is not just the rating or the milliamperes. The first thing is to identify what form of residual current may appear in the installation. That's the difference between installing an AC, A, F, or B type RCD, and between getting it right or leaving a weak point in the panel.
In a grid-connected photovoltaic system, the most sensitive part is associated with the inverter. Many inverters can generate continuous residual components or high-frequency residual currents. If the inverter manufacturer specifies a particular class of RCD, that prescription takes precedence. It is not a decorative recommendation. It is a technical condition for compatibility and safety.
Two zones must also be separated. On the one hand, the AC part downstream or at the inverter output. On the other hand, the DC part of the photovoltaic array, which requires specific protections and is not simply resolved with a conventional RCD. Mixing both planes is a common mistake in poorly tuned installations.
What type of RCD does a photovoltaic installation need?
AC type RCD
In photovoltaics, the AC type is usually the least recommended option. It is designed for sinusoidal AC residual currents and falls short when power electronics are involved. In the presence of inverters, frequency variation, or pulsating components, it may not provide the appropriate response.
Its use would only make sense in very specific circuits and always when expressly permitted by technical documentation. In professional practice, it is rarely the best choice for a current solar installation.
A type RCD
Type A detects AC residual currents and pulsating DC component currents. In many residential grid-connected photovoltaic installations, it is the usual starting point, but it's not enough to simply accept it out of habit. The inverter's data sheet must be reviewed to verify if it incorporates internal detection of continuous residual current greater than 6 mA.
If the inverter integrates this RDC-DD monitoring function or equivalent, in many cases a type A RCD can be accepted on the AC side. If it does not, a type A may be insufficient.
F type RCD
Type F becomes relevant when there are single-phase loads with electronics and a certain presence of mixed frequencies. It can improve performance against unwanted trips and offer a more refined response than a Type A in certain environments with inverters or sensitive equipment.
It is not the most widespread in all solar installations, but it can be an interesting option when seeking more immunity and better service stability in specific single-phase applications.
B type RCD
Type B is the reference equipment when there is a possibility of smooth continuous residual currents, in addition to AC and pulsating currents. It is the RCD usually required when the inverter does not guarantee continuous component limitation or detection, and also in certain three-phase configurations or equipment with more complex electronics.
It is a technically more complete solution, but also more expensive. Therefore, it is not about always installing it, but about installing it when appropriate. Oversizing the class unnecessarily increases the cost of the panel. Falling short compromises protection.
How to choose an RCD for a photovoltaic installation without errors
The first check should be made in the inverter documentation. This defines whether the manufacturer requires type A or type B, whether it accepts a standard or immunized RCD, and whether it incorporates 6 mA continuous leakage detection. Skipping this step later forces corrections on-site that could have been resolved during the selection phase.
The second variable is the network scheme and the number of phases. A residential single-phase installation is not the same as a three-phase installation in a warehouse or small business. This affects the number of poles of the RCD, usually 2P in single-phase and 4P in three-phase, and also the load distribution and the behavior of leaks.
The third decision is sensitivity. The 30 mA value is the most common for personal protection, but it is not always advisable to concentrate too many circuits or too much electronics under a single RCD of that sensitivity. In photovoltaics, filters and normal operating leaks can bring the installation close to the tripping threshold. When this happens, the catalog theory clashes with the reality of the panel.
Therefore, in installations with multiple lines, it is advisable to study selectivity, circuit distribution, and, if appropriate, immunized or super-immunized solutions. They do not eliminate a real leak, but they do reduce unwanted trips caused by transient disturbances, harmonics, or peaks associated with operations.
Unwanted trips in photovoltaics: why they occur
The most common problem is not that the RCD is faulty. It is that it is poorly chosen for the electrical context in which it operates. An inverter can generate small normal service leakage currents. Cables between strings and the inverter contribute capacitance. Internal filters also add up. If other receivers with electronics are also shared, the margin narrows.
When an RCD that is too sensitive, of the wrong class, or with low noise immunity is installed, random trips occur at dawn, when connecting production, during rapid load changes, or even during rearming operations. In these cases, changing an AC to an A, an A to an F or a B, or switching to an SI version, can resolve a recurring incident without touching the rest of the installation.
However, not every unwanted trip is fixed by changing the RCD. Sometimes there are real derivations, humidity in connectors, degraded insulation, or wiring errors. It is advisable to measure before replacing intuitively.
Immunized or auto-reclosing RCD in photovoltaic installations
When an immunized RCD is beneficial
In residential and light commercial photovoltaics, an immunized RCD makes a lot of sense when the panel coexists with electronics, variable frequency drives, switched-mode power supplies, or frequent maneuvers. Its advantage is not to increase the level of protection, but to improve service continuity by better filtering disturbances that trip conventional equipment.
For the installer, this translates into fewer call-outs due to trips without a permanent cause and fewer inspection visits due to intermittent incidents. In installations where the inverter operates near other sensitive receivers, it is usually a reasonable choice.
When an auto-reclosing RCD is advisable
Auto-reclosing can be useful in second homes, pumping, telecommunications, self-consumption with critical loads, or installations where prolonged disconnection leads to service losses. But it should not be installed routinely. It only makes sense when the risk has been thoroughly assessed and the equipment recloses under safe conditions.
In photovoltaics, moreover, it is necessary to review the compatibility between the RCD, its reclosing module, and the expected residual current typology. Not all auto-reclosing RCDs are suitable for every scenario or for every RCD class.
Rating, poles, and coordination with other protections
The RCD for a photovoltaic installation must also be coordinated with the nominal current of the circuit and with the associated circuit breaker. A 40 A 30 mA may be correct in many residential installations, but it is not a universal measure. If the line, the inverter output current, or the panel structure require a different nominal current, it must be adjusted.
In three-phase systems, it is common to work with 4-pole RCDs. In single-phase systems, with 2 poles. It seems basic, but selection errors still occur when panels are adapted or equipment is replaced without reviewing the entire system.
It is also advisable to consider the certification, CE marking, behavior curve, and actual quality of the equipment. In differential protections, price matters, but it does not compensate for saving on a reference that does not offer the correct class or that does not maintain stability in an environment with power electronics.
What to check before buying
Before ordering an RCD, it is practical to finalize five pieces of information: inverter type, class required by the manufacturer, single-phase or three-phase, nominal current, and required sensitivity. If there have also been previous trips, it is worth considering an SI version or a technically more immune solution.
In a specialized catalog like Bogas Electronics, this search is faster when working by specific reference: class A, F, or B, 2P or 4P, 30 mA, 40 A, three-phase format, immunized or auto-reclosing version. For the professional, this saves time and reduces compatibility errors.
The correct choice is not about installing the most expensive or the most common RCD. It is about installing the one that corresponds to the inverter, the network scheme, and the actual disturbance level of the installation. When this point is fine-tuned, the panel works stably, protection is consistent, and the customer stops calling due to trips that should not occur.
If a photovoltaic system causes problems, often the solution is not in the panels or the inverter, but in a properly specified RCD from the beginning.