In the modern electrical landscape, the “spare space” in a distribution board has become a luxury. With the rapid integration of EV chargers, solar inverters, smart home automation modules, and surge protection devices (SPDs), panel builders are facing a critical density challenge.
For decades, the standard configuration for residual current protection involved a “Split Load” board: one Residual Current Circuit Breaker (RCCB) feeding a bank of Miniature Circuit Breakers (MCBs). However, as ease of maintenance and business continuity become paramount, the industry is shifting toward the Residual Current Breaker with Overcurrent protection (RCBO).
This engineering guide analyzes the trade-offs between these two architectures, focusing on DIN rail real estate, Total Cost of Ownership (TCO), and selectivity in compliance with IEC 61009 a BS 7671.
Technical Definitions and Architecture
To make an informed procurement decision, we must first define the architectural differences defined by international standards.
The RCCB + MCB Configuration (Grouped Protection)
This architecture uses two distinct devices:
- RCCB (IEC 61008): Detects earth leakage currents (residual current) but offers ne protection against overloads or short circuits. It acts as the “gatekeeper” for a group of circuits.
- MCB (IEC 60898): Protects individual circuits against overloads and short circuits but ignores earth leakage.
In a typical “Split Load” board, one RCCB protects a busbar section feeding 4–8 MCBs. If the RCCB trips, all 8 circuits lose power.
The RCBO Configuration (Individual Protection)
. RCBO (IEC 61009) combines the functions of an MCB and an RCCB into a single device. It provides:
- Overload protection (Thermal)
- Short-circuit protection (Magnetic)
- Earth leakage protection (Core Balance Transformer)
Crucially, modern RCBOs fit this functionality into a single 18mm module width, matching the size of a standard MCB.
Space Analysis: The 18mm Module Calculation
Space is often the primary driver for switching to RCBOs. In the IEC standard, one module width (1TE) is 17.5mm to 18mm.
When designing a Pan Assembly in Distribution Boards, the calculation is straightforward. An RCBO protects a single phase and neutral (1P+N) typically within one module. An RCCB requires two modules (36mm) for single-phase or four modules (72mm) for three-phase.
Table 1: Space Usage Calculation (12-Circuit Single Phase Panel)
| Konfigurace | Ochranná zařízení | Total Module Width | Efektivita využití prostoru |
|---|---|---|---|
| Option A: Dual Split Load | 2 x RCCB (2-pole) + 12 x MCB (1-pole) | (2 x 2) + 12 = 16 Modules | Low: Requires extra space for RCCBs and cabling loops. |
| Option B: All RCBO | 12 x RCBO (1-pole sized) | 12 = 12 Modules | High: Saves 4 modules (72mm) – enough for a Surge Protection Device or smart meter. |
For panel builders, saving 4 modules often means the difference between fitting a standard enclosure or upgrading to a larger, more expensive custom cabinet.
Selectivity and Fault Isolation: The “Nuisance” Factor
While space is important, selektivitu (or discrimination) is the operational argument for RCBOs.
In a Grouped Protection (RCCB + MCB) scenario, a single earth fault on a minor appliance (e.g., a garden light or a toaster) will trip the main RCCB. This disconnects power to every MCB in that group.
- Consequence: A fault in the garage could turn off the Wi-Fi router, the fridge, and the home office computer. This is known as lack of discrimination.
In an RCBO installation, every circuit is independent. A fault on the garden light trips pouze the garden light’s RCBO. The rest of the house remains powered. For commercial applications like data centers or hospitals, this level of Selektivita is mandatory to prevent costly downtime.
Table 2: Selectivity Comparison Matrix
| Funkce | RCCB + MCB (Grouped) | RCBO (Individual) |
|---|---|---|
| Fault Discrimination | Poor. 1 fault affects multiple circuits. | Excellent. 1 fault affects 1 circuit. |
| Cumulative Leakage | High Risk. Healthy leakage from multiple PCs/devices sums up and may trip the shared RCCB. | No Risk. Leakage is managed per circuit. |
| Diagnostics | Difficult. User must manually check 4-8 MCBs to find the faulty circuit. | Instant. The tripped handle identifies the exact faulty circuit immediately. |
| Critical Uptime | Not recommended for servers/medical. | Highly recommended. |
Cost Analysis: Hardware vs. Installation vs. Lifecycle
The primary objection to RCBOs is usually the upfront unit cost. An RCBO is more complex to manufacture than a simple MCB. However, looking at the hardware cost in isolation is a mistake often made by procurement teams. One must calculate the Celkové instalované náklady.
Table 3: 10-Year Cost Breakdown (Commercial Office Example)
| Nákladová složka | RCCB + MCB Strategy | RCBO Strategy | Analýza |
|---|---|---|---|
| Hardware Cost | Low ($) | Medium ($$) | RCCB + MCBs is approx. 20-30% cheaper in pure materials. |
| Instalační práce | High ($$$) | Low ($) | Split load boards require complex neutral bar wiring and busbar cutting. RCBOs plug-and-play. |
| Wiring Materials | Medium ($$) | Low ($) | RCBOs eliminate the need for extensive neutral cabling kits. |
| Maintenance/Downtime | High ($$$) | Low ($) | Cost of one office blackout caused by a shared RCCB trip usually exceeds the hardware savings. |
| Total 10-Year Cost | Vysoká | Nízká | RCBO wins on TCO. |
Furthermore, simplified wiring reduces the risk of installer error, specifically “Neutral Borrowing” or “Crossed Neutrals,” which are notoriously difficult to troubleshoot in Split Load boards.
Application Matrix: Choosing the Right Strategy
Not every installation requires 100% RCBOs. A hybrid approach often yields the best balance of cost and performance.
Table 4: Recommended Applications
| Aplikace | Recommended Strategy | Odůvodnění |
|---|---|---|
| Residential (Budget) | Hybrid | Use RCBOs for critical circuits (Fridge, Alarm, Home Office). Use RCCB+MCB for Lighting/sockets. |
| Residential (High-End) | Full RCBO | Prevents nuisance tripping from modern appliances (washing machines, EV chargers) with high earth leakage. |
| Commercial Office | Full RCBO | Computer downtime cost is prohibitive. High density of IT equipment causes cumulative leakage that trips shared RCCBs. |
| Průmyslové řízení | Full RCBO | Motor drives (VFDs) introduce harmonic leakage. Individual Type A or B RCBOs are essential. |
| Exterior/Landscape | RCBO | Outdoor circuits are prone to moisture ingress. Isolate them to prevent tripping the main building power. |
Technical Considerations: Modern Loads and Standards
Handling DC Leakage (Type A, F, and B)
Modern electronics—including LED drivers, washing machines, and EV chargers—generate DC components in the leakage current. Standard AC Type RCCBs can be blinded by this DC current.
- Nabíjení elektromobilu: Requires Typ B protection or Type A with 6mA DC detection. Installing a Type B RCCB to protect a group of MCBs is incredibly expensive. Using a single Proudový chránič typu B for the EV circuit is far more cost-effective.
Vnitřní součásti
The engineering challenge of the RCBO is miniaturization. Combining the toroidal transformer of an RCCB and the arc chutes of an MCB into 18mm requires precise thermal management. VIOX engineers use high-grade bi-metals and compact electronic PCBs to ensure heat dissipation complies with IEC 61009 temperature rise limits.
Závěr
While the RCCB + MCB configuration remains a valid, low-cost solution for simple residential applications, the RCBO has emerged as the professional standard for modern electrical distribution.
The “Space Crisis” in panels, driven by renewable energy and automation integration, makes the 18mm footprint of the RCBO invaluable. When combined with the operational benefits of full selectivity and reduced wiring labor, the RCBO offers a superior Return on Investment (ROI) for contractors and end-users alike.
For VIOX partners, recommending RCBOs is not just about upselling hardware; it is about delivering a resilient, future-proof electrical system that minimizes downtime and simplifies maintenance.
ČASTO KLADENÉ DOTAZY
Can RCBO completely replace RCCB+MCB combination?
Yes. An RCBO provides the exact same protection functions (Overload, Short Circuit, and Earth Leakage) as an RCCB and MCB combined, often with better performance regarding selectivity.
What are the space savings in a typical 12-circuit panel?
In a 12-circuit single-phase board, using RCBOs typically saves 2 to 4 module widths (36-72mm) compared to a dual split-load RCCB arrangement, allowing for a smaller enclosure or more space for wiring.
Is RCBO more expensive than RCCB+MCB?
Hardware-wise, individual RCBOs are generally more expensive than buying one RCCB and several MCBs. However, when you factor in the reduced installation time (labor) and simpler cabling, the total project cost difference is minimal, and often cheaper for the RCBO option in complex boards.
Which configuration offers better selectivity?
RCBOs offer superior selectivity. If a fault occurs, only the specific RCBO for that circuit trips. With an RCCB+MCB setup, the main RCCB trips, disconnecting power to all MCBs associated with it (often 4-8 circuits).
What about maintenance and long-term reliability?
RCBOs simplify maintenance because fault finding is instant—you know exactly which circuit has the earth fault. Reliability is comparable, though RCBOs reduce the number of connection points (potential failure points) inside the board.
When should I choose RCCB+MCB over RCBO?
Choose RCCB+MCB for budget-critical residential projects where minimizing upfront hardware cost is the only priority, and where “nuisance tripping” (losing multiple circuits at once) is considered an acceptable inconvenience.
