The RCCB (Residual Current Circuit Breaker)—the switch in the distribution box featuring a “T” test button—is designed specifically to prevent electric shock. However, it is not a cure-all; it must be used correctly to function effectively.
An RCCB protects only against earth leakage; it does not handle overloads or short circuits. If you install only an RCCB, it will not trip in the event of wire overheating due to overload or sparking caused by a short circuit. Therefore, an MCB (Miniature Circuit Breaker) must be installed upstream or downstream of the RCCB; the MCB handles overload and short-circuit protection, while the RCCB is dedicated to earth leakage protection.
Residential RCCBs are typically rated at 30mA, a threshold intended to ensure personal safety. However, 30mA may be insufficient for preventing electrical fires; persistent minor leakage—even if below the 30mA threshold—can still ignite surrounding materials. If fire protection is required for the main incoming line, a 100mA or 300mA RCCB should be selected and used in coordination with downstream 30mA protection devices.
| Application | Recommended Tripping Current | Recommended Tripping Time |
| General household main distribution board / socket circuits | ≤ 30 mA | ≤ 0.1 s |
| Damp or corrosive environments (e.g. bathrooms, kitchens) | ≤ 15 mA | ≤ 0.1 s |
| Exceptionally damp locations with good conductivity (e.g. underwater, inside metal enclosures) | ≤ 10 mA | ≤ 0.1 s |
The button marked “T” on the RCCB is the test button. If the switch trips immediately when pressed, the earth leakage protection function is working correctly; if it does not trip, the device has failed and must be replaced. It is recommended to make a habit of testing it once a month. Many earth leakage protection devices remain inactive for years, only for users to discover they are already broken when an actual incident occurs.
What should you do if the RCCB trips? This indicates a current leakage in the circuit or an appliance. First, unplug all electrical appliances and flip the switch back on one by one to identify the specific circuit or appliance causing the leakage. If it trips immediately upon being switched on, the problem lies within the wiring itself, requiring professional troubleshooting. Repeatedly forcing the switch back on effectively renders the protection device useless and poses a significant danger.
The RCCB is just one component of an electrical safety system, not the whole system. It is designed to be used in conjunction with an MCB; you should press the test button monthly, and if it trips, troubleshoot the issue before resetting the switch. Only when used correctly does it serve as a true “life-saving switch.”
