Why does my circuit breaker keep tripping? Overload vs short circuit

Q: Why does my circuit breaker keep tripping?

A circuit breaker (MCB) trips for three reasons: overload (too much running on one circuit), short circuit (line touching neutral or earth, trips instantly) or a faulty appliance. If it trips the moment you switch it on, look for a short circuit. If it trips after a few minutes under load, the circuit is overloaded.

For 230/400 V installations to IEC standards (Europe, UK and most of the world). North America uses different voltages, colours and rules: see the “Around the world” notes.

First: when does it trip?

Symptom	Likely cause	What next
Trips instantly when you switch it on, nothing works	short circuit in the wiring or in a fixed appliance	unplug everything on the circuit and reset: holds → appliance fault; still trips → wiring fault, call an electrician
Trips after several minutes under heavier load	overload: too much power on one circuit	spread the load, do not run a heater and a kettle on one socket
Trips when one particular appliance starts	faulty appliance (washer, microwave, charger)	unplug it, get it repaired
Trips "randomly", even at night	damaged insulation, damp box, chewed cable	insulation resistance test by an electrician

If it is not the circuit breaker but the RCD that trips, the cause is leakage, not overload: see why an RCD keeps tripping.

What NOT to do

Never fit a bigger breaker (for example B16 to B25) "so it holds". The cable is sized for the breaker. A bigger breaker lets the cable in the wall overheat before anything trips.
Do not tape or jam the lever, do not bridge the protection.
Do not keep resetting onto a short circuit: the arc damages the contacts.

How to narrow it down

Unplug everything on the circuit (sockets) or switch off all lights (lighting circuit).
Reset the breaker. If it holds, plug things back in one at a time until it trips: that is your culprit.
Trips with nothing connected? The fault is in the wiring: you need an electrician and tests.

Around the world: the logic is the same everywhere. Old installations may have rewirable or cartridge fuses instead of breakers; a blown fuse means the same thing as a tripped breaker, and the replacement must have the same rating, never higher.

Important: if a breaker trips together with a burning smell, smoke or hot accessories, leave the circuit off and call an electrician. Finding short circuits and testing insulation is work for a qualified person.