The components of an electrical panel: breakers, RCDs, SPDs and their roles
The electrical panel is the “brain” of the installation in any home or commercial space: this is where energy is distributed across circuits and, more importantly, where all the protections that safeguard people and appliances are concentrated. Before installing or upgrading a panel, it is worth understanding what each component does and why none of them can be left out. Below you will find a clear explanation of each element, with its role, typical ratings and the most common mistakes.
What an electrical panel actually is
The electrical panel (also called a distribution board) is the box into which the supply cable enters after the meter and from which the circuits run out to sockets, lighting, the boiler, the hob, the water heater and so on. Its role is twofold: it distributes energy in an organised way, across separate circuits, and it protects the installation and its users by means of dedicated devices.
A properly designed panel complies with the I7 standard and is installed by qualified personnel. For a new electrical connection (bransament) or when upgrading the installation, the panel is sized according to the power approved through the technical connection approval (aviz tehnic de racordare) and the number of circuits required.
The main components of an electrical panel
1. The main switch (isolator)
This is the device from which the supply to the entire panel is switched off. It allows the whole installation to be de-energised so that work can be carried out safely. On small panels this can be a main circuit breaker, while on larger ones it is a load isolator.
2. Miniature circuit breakers (MCBs)
The MCB (Miniature Circuit Breaker), also known as an automatic circuit breaker, protects the cable and the circuit against two types of fault:
- Overload – when consumption exceeds the rated current for a longer period (thermal tripping).
- Short circuit – when a direct phase-to-neutral contact occurs (electromagnetic, instantaneous tripping).
The MCB does NOT protect a person against electric shock. It protects the conductor so that it does not overheat and cause a fire. The rated value (e.g. 10A, 16A, 20A, 25A) is chosen according to the cross-section of the cable and the circuit.
3. The residual current device (RCD) and RCBO
The residual current device, or RCD (Residual Current Device), is the component that protects people against electric shock. It permanently measures the difference between the current flowing in through the phase and the current returning through the neutral. If part of the current “escapes” to earth (for example through the body of a person touching a faulty wire), the RCD trips within a few milliseconds.
The reference value for personal protection is a sensitivity of 30 mA. For socket circuits, bathrooms, kitchens and outdoor areas, a 30 mA RCD is effectively mandatory.
There is also the RCBO, a combined device that incorporates into a single module both the function of an MCB (overload + short circuit) and that of an RCD. It is the modern, compact solution, which ensures that a fault on a single circuit does not leave the whole house without power.
4. The surge protective device (SPD)
The SPD (Surge Protective Device) protects electronic appliances against transient overvoltages: nearby atmospheric discharges (lightning), switching events on the distribution grid, line faults. Without an SPD, a surge can destroy televisions, boilers, electronics and household appliances in an instant.
SPDs are classified by type (Type 1, Type 2, Type 3) according to their level of protection and their position in the installation. For a home connected to the overhead grid, a Type 2 SPD installed in the panel is the usual recommendation; in areas at risk of a direct lightning strike, Type 1 + Type 2 are combined.
5. The voltage relay (under/overvoltage protection)
Unlike the SPD (which responds to short-duration surges, on the order of microseconds), the voltage relay protects against sustained over- and undervoltages – for example when the neutral on the grid breaks and the voltage rises to 300–400 V. It is very useful in areas with an unstable grid and is often fitted on three-phase connections, where an imbalance between phases can be dangerous.
6. The neutral (N) and earth (PE) bars
In the panel there are bars (collector terminals) to which the working neutral (N) and protective / earthing (PE) conductors are connected. The PE conductor is essential for the operation of the protections and for channelling fault currents towards a properly executed earthing electrode. Without good earthing, the RCD and the rest of the protections cannot fully perform their role.
7. The meter and the metering block
The energy meter usually belongs to the distribution operator (Retele Electrice Romania S.A.) and is installed in the metering block at the property boundary, not necessarily in the indoor panel. When connecting a photovoltaic system, the operator installs a bidirectional meter (smart meter), which is required for connection as a prosumer.
Comparison table: what each component protects
| Component | What it protects | Type of fault | Typical value |
|---|---|---|---|
| MCB | The cable / circuit | Overload, short circuit | 10A, 16A, 20A, 25A |
| RCD | People | Fault current to earth | 30 mA (homes) |
| RCBO | The cable + people | Overload, short circuit, earth fault | 16A / 30 mA |
| SPD | Electronic appliances | Transient surges (lightning) | Type 2 (home) |
| Voltage relay | Appliances | Sustained under/overvoltage | 170–270 V (threshold) |
| PE bar | The entire installation | Lack of a fault path | – |
How circuits are organised within a panel
A well-designed panel divides the loads across separate circuits, each with its own protection. A typical apartment layout includes:
- Lighting circuit – 10A breaker;
- Socket circuits – 16A breakers, behind a 30 mA RCD;
- Kitchen / large appliance circuit – dedicated, 16–20A;
- Water heater / washing machine circuit – with its own RCD;
- Boiler circuit – separate, so that you are not left without heating in the event of a fault on another circuit;
- Hob / oven circuit – at 25A or on three-phase, as appropriate.
Separating loads across circuits has a practical advantage: a fault on a single circuit does not leave the whole home without power. If you want to add new circuits or move to a higher power level, you may need a power upgrade (spor de putere) or a switch from single-phase to three-phase.
Common mistakes with electrical panels
- The absence of a 30 mA RCD – the most serious one, because personal protection disappears.
- A single RCD for the whole panel – in the event of a fault, the entire house is left without power; the modern solution is RCBOs on individual circuits.
- The absence of an SPD on overhead connections, which are exposed to lightning.
- Non-existent or poor earthing, which cancels out the effectiveness of the protections.
- Oversized breakers relative to the cable cross-section – risking that the conductor is no longer protected.
- Careless connections at the bars, which produce overheating and electric arcing.
Periodic checking of the earthing and of the continuity of the protections is carried out through PRAM measurements, recommended both on the acceptance of a new installation and periodically thereafter.
Conclusion
A safe electrical panel does not mean “as many breakers as possible”, but rather the right protections, correctly sized and correctly connected: MCBs for the cables, 30 mA RCDs for people, an SPD for appliances and solid earthing so that everything works. The installation and upgrading of a panel must be carried out by an ANRE-certified company, which is responsible for the compliance of the installation.
SUN WATT SRL (bransam.ro) carries out and designs electrical connections, grid connections and electrical installations in Bucharest, Ilfov and Giurgiu. For a new panel, an upgrade or an inspection, you can call us on 0733 097 440 or write to us via the contact page.