Quick answer
If an MCB trips after running a while, the circuit is usually overloaded; if it trips instantly, look for a short circuit. If an RCCB trips, something is leaking current to earth, often a geyser, an appliance or damp wiring. Never hold a breaker on or replace it with a bigger one.
MCB tripping: common causes
| What you see | Likely cause | What to do |
|---|---|---|
| Trips after some minutes or hours | Overload: too many appliances on one circuit | Move loads to another circuit, or have the circuit upgraded with bigger wire and MCB |
| Trips instantly when switched on | Short circuit in the wiring or an appliance | Unplug everything; if it still trips, the fault is in the wiring: call an electrician |
| Trips when a motor, pump or AC starts | Starting current too high for a B curve MCB | A C curve MCB of the same rating usually suits; D curve for motors |
| MCB is hot, or trips at light load | Loose terminal or an old, weak MCB | Have the connections tightened, or replace the MCB |
RCCB tripping: common causes
| What you see | Likely cause | What to do |
|---|---|---|
| Trips when the geyser or an appliance switches on | Leakage in that appliance, often a geyser element | Unplug it and test the RCCB again; have the appliance repaired |
| Trips in the monsoon or after rain | Moisture in outdoor points, junction boxes or old wiring | Find and dry or seal the wet point |
| Trips at random, nothing obvious | Neutrals of different circuits mixed, or many small leakages | An electrician should check that each RCCB has its own neutrals |
| Will not reset at all, even with nothing connected | Faulty RCCB or a wiring fault | Have it tested; replace if faulty |
Finding the cause safely
- Switch off or unplug every appliance on the circuit.
- Reset the breaker. If it trips with nothing connected, the fault is in the wiring: stop here and call an electrician.
- Switch the loads on one at a time. The one that trips it is the culprit.
- Press the RCCB's T (test) button once a month: it should trip. If it does not, replace the RCCB.
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Values are typical guidance for Indian 230 V single-phase and 415 V three-phase supplies. Always follow the equipment nameplate, the manufacturer's instructions and your licensed electrician, who is responsible for the final selection and installation.