MCB keeps tripping: finding the appliance that causes it without opening the panel

• Switch off the MCB and unplug the appliance before checking anything.
• Make sure your hands and the floor are dry.

Nothing in this article asks you to remove the cover of the panel, a fuse box, a socket or a switch. You only touch the MCB lever from the outside, plugs, and the buttons on appliances.

An MCB is an automatic circuit breaker. It cuts the power when the current through it exceeds its limit, for example because too many large appliances run at the same time. It also cuts the power when there is a short circuit, for example when bare wires touch each other. Many homes also have an ELCB, or an MCB with earth leakage (ground fault) protection, which cuts the power when current leaks to an appliance's metal body or to the ground. Modena's Onyx water heater manual, for example, calls for a circuit breaker with earth leakage protection rated for the heater's power.

So a tripping MCB is not the enemy. It is protecting the wiring and the people in the house. Flipping the lever up again and again without looking for the cause, or swapping it for a bigger one so it stops tripping, takes that protection away. Your job is to recognize the pattern: does it trip from an overload, from one particular appliance, or from a problem in the wiring?

In Indonesian homes the MCB is usually in one of two places: in PLN's electricity meter box at the front of the house, or in the group panel inside. Note which one trips, because that is a useful first clue for the electrician.

1. Write it down first. Note when the MCB tripped, which appliance had just been switched on, whether it was raining, and which MCB tripped. These notes are often more useful than trying again and again.
2. Switch off the large loads. Switch off and unplug high-power appliances such as the AC, water heater, water pump, washing machine, iron, rice cooker and water dispenser. If the AC has its own dedicated breaker, switch that breaker off.
3. Flip the lever up once. With dry hands, push the lever of the tripped MCB back up. If it trips again right away even though the large loads are off, do not try again. That points to a wiring fault, so go straight to the section on when to call an electrician.
4. Turn them on one by one. If the lever stays up, switch the appliances on one at a time, a few minutes apart, starting with the smallest. Note which appliance trips the MCB.
5. Repeat to be sure. If the same appliance trips the MCB twice, the problem is most likely in that appliance. Stop using it and look over its plug and cord from the outside.
6. If it only trips when loads pile up. This points to more load than the circuit can carry. Avoid running large appliances at the same time, for example by not ironing while the water heater and pump are on.

Many faults start with a poor connection, not with the appliance. LG asks AC owners to check that the plug sits firmly and to look for burn marks on the socket slots or the plug. A loose or scorched socket must be replaced by a qualified electrician. According to LG, a loose power cord can overheat and cut the power.

How things are plugged in matters too. LG recommends plugging the AC straight into a dedicated wall socket, not through a power strip or extension cord. Sharp's refrigerator manual says to plug it straight into the wall socket without an extension cord or adapter, and forbids putting power strips behind the refrigerator. Modena's split AC manual calls for a single socket and a circuit breaker that match the ratings on the AC, and for SNI-certified cable (the Indonesian National Standard) of suitable capacity. For storage water heaters, the Modena manual says the socket must be rated at no less than 16A and must be properly grounded.

Some air conditioners have a feature that helps. The Daikin FTXTM-R manual describes a function that caps the maximum power consumption, so the circuit breaker does not trip when the AC runs at the same time as other appliances. Check your AC's manual for a similar feature.

Earth leakage is often linked to water and moisture, so suspect appliances near water first: the water heater, water pump, washing machine, and sockets in the bathroom or on the porch. Many electric water heaters have their own ELCB in the plug. The Modena water heater manual explains how to test it: press the test button, and the indicator light should go out and the reset button pop up; press reset, and the light comes back on. If the reset button cannot be pressed in, the ELCB is faulty. If you press reset and it pops up again, the circuit is leaking or the power is off.

The same manual forbids powering the water heater through an external switch such as a timer, to avoid accidental resetting. Modena's instant water heater manual says to check the built-in ELCB once a month and to switch off the MCB during lightning storms to protect the water heater from damage.

If the house ELCB trips again and again when it rains, do not dry out or open up connections outside the house yourself. Note the times and let an electrician track down the wet spot.

This is the most important part of this article. Stop and call a qualified electrician if:

• the MCB trips again right away even though every appliance is unplugged and every switch is off;
• you smell burning, hear hissing or crackling from the panel, a socket or a switch, or the panel feels hot;
• a socket or plug is loose, melted or scorched (LG says a qualified electrician should replace it);
• the ELCB trips repeatedly, especially when it rains, or a wall or socket is damp;
• water has reached the panel, a cable or a socket;
• the MCB lever feels loose or will not stay up, or the MCB feels hot when you touch it from the outside.

Opening the MCB panel, replacing the MCB, repairing in-wall wiring and checking the grounding are jobs for an electrician, not for the people living in the house. If one particular appliance is the trigger, take it to that brand's authorized service center. If the MCB that trips is the one in the meter box, contact PLN through its official channels. Never fit a bigger MCB just to stop the tripping; the cables in the wall do not get any thicker.