⚠️ CRITICAL SAFETY WARNING: READ BEFORE PROCEEDING ⚠️
This information is for EDUCATIONAL PURPOSES only. It is provided to help you, the reader, understand the necessary safety devices (like MCBs, RCCBs, SPDs, and proper switches) required for electrical protection in your home, office, or shop.
DO NOT ATTEMPT TO INSTALL OR WORK ON ELECTRICAL SYSTEMS YOURSELF.
Electrical work can be highly dangerous, leading to severe injury, fire, and property damage if done incorrectly. You MUST hire a licensed and qualified electrician to design, install, and certify any new or modified electrical system.
ACTIONABLE ADVICE FOR YOUR PROPERTY’S SAFETY:
Many buildings, especially older ones, were constructed without the modern, essential safety devices like RCCBs (Residual Current Circuit Breakers), leading to a high frequency of electrical fires and fatal shocks.
For all buildings, new and old:
- ADVISE YOUR ELECTRICIAN to install all necessary protection devices as per national and local electrical codes (e.g., MCBs, RCCBs/RCDs, and SPDs).
- Even if you own an old building, please learn and prioritize the upgrade of your existing electrical panel to include these life-saving devices. Your safety depends on it.
The most robust and compliant sequence ensures that the most sensitive devices (like the RCCB and final loads) are protected by the less sensitive, high-current devices (like MCBs and SPDs).
This sequence applies to the Load Side of the AC Changeover Switch (i.e., the power that feeds your home circuits):
Power Source (Grid or Inverter) – Main Isolator/Switch – SPD – MCB (Main) – RCCB – Branch MCBs – Loads
Here is the component list with the recommended connection order from the output of the Changeover Switch to your final home circuits:
| Device | Role in the System | Recommended Position |
| 1. Main Isolator/Switch | Total isolation of the board from either source (Grid or Inverter). Crucial for maintenance. | First device in the DB (after the changeover switch). |
| 2. Main SPD (Surge Protection Device) | Protects everything that follows (MCB, RCCB, and loads) from large, transient voltage spikes. | Second in line, connected before the main current protection. |
| 3. Main MCB ( MCCB FOR HEAVY LOAD) | Primary Overcurrent Protection. Protects the main wiring and busbars of the DB from a massive short circuit or overload. | Third in line, provides backup protection for all downstream devices. |
| 4. RCCB (Residual Current Circuit Breaker) | Essential Human Safety. Provides earth leakage/electric shock protection for a group of circuits. | After the Main MCB to protect the most sensitive device (the RCCB) from overcurrent/shorts. |
| 5. Branch MCBs | Circuit Protection. Protects individual final circuits (sockets, lights, A/C unit, etc.) from overloads and shorts on that specific line. | Final output devices before the circuits go to the house loads. |
Key Modification and Why:
- Placement of SPD:
- Reasoning: Placing the SPD after the main switch/isolator but before the Main MCB/RCCB ensures it can safely dump a surge to the earth line before it reaches the other components. It protects the integrity of the expensive breakers that follow.
- Using a Main MCB before the RCCB:
- Reasoning: As detailed in the blog post, the MCB (overcurrent protection) must come before the RCCB (leakage protection). This ensures the RCCB itself is protected from high-current damage if a fault occurs.
Summary of Final AC DB Layout
For a robust solar home setup, the power flow should be:
- GRID LINE
- SOLAR INVERTER AC OUT
- (Both lines feed into…)
- Automatic or Manual CHANGE-OVER SWITCH (ATS/MTS)
- (The selected output then feeds into the…)
- HOME AC DISTRIBUTION BOARD
- Main Isolator (for full safety isolation)
- SPD (Surge Protection)
- Main MCB (Overcurrent Protection for the DB)
- RCCB (Earth Leakage Protection – may be one main one, or several protecting groups of circuits)
- Individual Branch MCBs (Final Load Protection)
- Loads (House Circuits)
Always consult with a certified electrician who is familiar with your local electrical codes (NEC, IEC, etc.) before finalizing and installing any wiring plan. They will ensure correct component ratings (Amperage, sensitivity, and pole numbers) for your specific loads and inverter size.