Why DB boxes catch fire: what Malaysian electricians find inside, and how it's fixed

When a DB box burns, the breakers usually weren’t the problem. In the burnt boards Malaysian wiremen and homeowners post, the damage almost always starts at a screw terminal where a cable lands: the main switch’s incoming or outgoing terminal, the neutral bar, an RCCB terminal, a busbar that wasn’t seated. A joint that isn’t gripping copper properly heats up, and none of the devices in a home DB are designed to notice.

What follows comes from burnt-board cases and repair discussions in Malaysian electrical Facebook groups, checked against Bomba, ST, TNB and manufacturer sources.

The numbers behind it

Bomba (JBPM) attributes about 60% of house fires in Malaysia to electrical problems. The Director-General gave the figure in August 2025 without a year or case count. Bomba’s investigators split electrical causes into short circuit, overload and resistance heating, which means a bad connection getting hot. In Melaka, resistance heating was the largest cause of building fires from January to July 2025: 201 cases, which the state put at 65%. The state director described it in a sentence: “apabila wayar elektrik tak ketat dia akan longgar dan akan berlaku lompatan atau ‘spark’” (when a wire isn’t tight it works loose and sparks).

Home DBs do start fires. After the February 2024 fire at Flat Sri Sabah in Cheras, which spread to five units, Bomba KL’s forensic team said they were 90% sure it started at the unit’s DB. News reports often say “litar pintas” (short circuit) for any electrical fire. In the cases below, a true short is the exception.

What the burnt boards show

A few cases show how these play out.

Main switch and RCCB, Bentong, 2023. A neighbour asked the poster to look at a DB with burn marks on it. When it was opened, the RCCB had burnt open (“berlubang dibuatnya”) and the 63A main switch beside it was burnt too. The photos show the main switch’s outgoing terminal and its cable charred and the housing burnt through, and the RCCB’s top terminals blackened. The post gives no cause, but the damage sits exactly at the terminals, the pattern of a joint that overheated.

Neutral bar, Shah Alam, 2026. Two separate jobs. In one, on Jalan Kebun, a neutral bar burnt at its end screw because the screw was loose; the photos show the neutral’s insulation melted and the bar corroded green, and the wireman replaced the bar. In the other, the owner saw flames at the DB. A loose neutral had been making the voltage unstable for some time, and the wireman ended up replacing four fans and 22 lamps.

RCCB after a meter change, 2026. A homeowner’s house tripped two or three times and the lights blinked “macam tak cukup karan” (like there wasn’t enough power) for about a week after a TNB contractor replaced the meter. Then it tripped again, smelled of burning and the DB was hot and smoking. The photo shows the RCCB’s top terminal and its cable charred. Flickering lights were the warning.

MCB at 68°C on a 2A load. A wireman posted a thermal camera reading from an MCB that was hot even though it carried about 2A, its screws were tight and there was no short, and asked the group to guess why. The most-liked practical answer (22 reactions) was “screw cable ketat, tapi kepit pada PVC, tak kena direct pada copper”: the screw was tight on the insulation, not the copper. Others added partly gripped strands, copper nicked during stripping, a cross-threaded screw that feels tight while the cable is still loose, and sooted contacts inside the MCB. One reply summed it up as traffic: three lanes squeezed into one. Wherever the current path narrows, it heats.

DB fire in a solar installation, 2026. Two years after a solar system went in, its DB caught fire and the original installer stopped answering calls. The owner switched the system off and smothered the flames with a damp cloth. Another installer who was called in found soot up the wall above the board and burnt cable at its side. He checked the cable size was right and said loose cable terminations are the usual cause of fires like this.

Busbar in a three-phase showroom DB, Nilai, 2026. A three-phase pin busbar with a burnt spot where it fed a three-pole MCB. The electrician put it down to heating from a high-resistance contact.

Why the breakers don’t stop it

An MCB trips on overload or a short. An RCCB trips when current leaks to earth. A loose joint is neither: the current is normal, and it all returns through the neutral. So a joint can overheat for weeks, charring its insulation, while every breaker stays on. Schneider’s own installation guide says these arcs “are not detected by residual current devices, circuit breakers, or fuses”. One poster asked how an RCCB could “trip tapi boleh lebur” (trip, but still melt). The replies called it a loose connection, and pointed out that the board had no main switch: the incoming cable went straight into the RCCB.

The device that does detect arcing is an arc fault detection device (AFDD). The international wiring standard (IEC 60364) now calls for them on some circuits, but neither Schneider’s nor Hager’s Malaysian catalogue lists one.

Warning signs

These come up again and again in the cases:

• A burning or “hangit” smell near the DB.
• A warm DB cover, or one breaker noticeably hotter than its neighbours.
• Brown or blackened plastic or insulation around a terminal.
• Lights flickering when a heavy load like the water heater comes on. In one case the cause wasn’t even the DB: TNB’s cut-out fuse outside had a loose, taped-up carrier that sparked under the heater’s load.
• Lamps blowing and fans racing. That’s an unstable neutral: the voltage on some circuits rises towards 400V. One street had appliances “suddenly on fire” in several houses. Note which lights went bright before the trip, list what got damaged and gather the neighbours’ complaints; that pattern points to a lost neutral on the supply side.
• Trips that started right after work on the meter or the board.

What to do on the night

If there’s smoke, flames or melting, keep away from the board and call 999. Don’t put water on it; when the solar-case owner used a damp cloth, electricians in the thread said a dry-powder or CO2 extinguisher is the right tool. If the main switch is away from the burning part and you can reach it without touching anything hot, switching it off cuts the house circuits. If the main switch itself is what’s burning, as in the Bentong case, leave it. Either way the cable between the meter and the main switch stays live until the supply is cut at TNB’s cut-out.

If it’s a smell, heat or flicker without fire, switch off the circuit or main switch and don’t keep resetting it. Call a wireman (pendawai) working for an ST-registered electrical contractor. An ordinary single-phase home needs a wireman certified for single-phase work; a three-phase home needs one certified for three-phase. Malaysia’s Electricity Regulations (reg. 111) reserve repair and replacement of installation equipment for a competent person.

If the damage is at the meter or cut-out fuse, or the problem is on the street side, it’s TNB’s: their supply handbook says the meter and service cut-out are TNB’s equipment. Call TNB on 15454. In one case TNB came quickly to replace a sparking cut-out carrier. A shop owner was told a too-hot-to-touch cut-out was “normal”. Some electricians who replied agreed it gets hot under heavy load, but most said to measure each phase’s current and look for a loose contact or overload. TNB also estimates that about 60% of the outages it’s called to are faults in the customer’s own wiring, so check your own DB first.

What a proper repair looks like

The cheap fix is to tighten the screw, tape over the cable and switch back on. Several cases show why that isn’t enough.

• Replace what overheated. A terminal that has burnt has softened its plastic and oxidised its metal; tightening it again doesn’t restore it. Electricians in these cases replaced the main switch, RCCB, MCB or neutral bar involved.
• Cut the cable back to sound insulation, or replace it. In one recent case a crew cut out the burnt pieces after a DB fire and spliced new cable in the board. Afterwards a test pen lit up on the cable and the owner asked the group why. Replies split: some said a non-contact test pen glows near any live cable, others suspected heat-damaged insulation and leakage. A test pen can’t settle that; an insulation-resistance (“megger”) test can. Cable that has cooked near a burnt terminal is better replaced back to sound insulation than joined.
• Terminate properly. Strip to the right length, push the copper fully in, no insulation under the clamp, no nicked or cut strands. Don’t force several conductors into a hole meant for one; use a longer bar or a proper connector. One wireman fixed a neutral that had welded itself to the bar by fitting a longer neutral bar. For main cables, some use crimped cable ends.
• Tighten to the maker’s torque, with a torque screwdriver. Feeling tight isn’t the test: a cross-threaded screw can feel “ketat level Mike Tyson” with the cable still loose, and overtightening strips threads. The UK’s Electrical Safety First warns against tightening terminals with a battery drill. The figures differ by brand. Schneider gives 3.5 N·m for Easy9 MCBs, Easy9 RCCBs and Acti9 iC60. Hager gives 2.8 N·m for its MU MCBs and CD RCCBs, and 2.1 N·m for its AD RCBOs.
• Fix whatever made it run hot. A circuit carrying a heavy continuous load needs the right cable and breaker. ST’s domestic wiring guideline sets the minimums: 10mm² main cable up to a 40A main breaker, 16mm² up to 63A, 2.5mm² for socket circuits, 4–6mm² for aircond and water heater circuits. A 32A MCB on a lighting circuit, 1.5mm² cable on sockets, or a meter cable wired straight into an RCCB with no main switch all turned up in the same call-outs.
• Check the neutral and the supply if lamps or appliances died: measure each phase to neutral, phase to phase, and neutral to earth.

Heavy new loads: EV chargers, water heaters, aircond

New continuous loads find weak joints quickly. A homeowner asked why the RCCB and MCB in the small DB feeding a 7kW EV charger ran hot at 20A on 6mm² cable. The most-liked reply said to open it up and check the terminations (“buka tgk termination”), since 6mm² is enough for a 7kW wallbox. Others preferred 10mm² and a separate RCCB or DB fed from the main board’s incoming side rather than tapped off an outgoing circuit. Another owner lost power after the first 45-minute home charge when TNB’s cut-out fuse burnt.

Aircond on a 13A socket came up too: in one house the socket’s neutral terminal melted. Some replies said a 1hp inverter unit draws under 4A, so a socket is fine; others recommended a 20A double-pole switch or a direct 20A point. Several put the melting down to a bad contact at the socket terminal. Our aircond guide and water heater guide cover the right circuits for those loads.

Prevention: what’s worth doing

• Have the DB checked under load, especially an older one. No law requires periodic checks of homes: the Electricity Regulations exempt domestic installations from the five-yearly testing required elsewhere. Bomba advises an inspection every 10 to 15 years. Wiremen advertising in the groups say every two to five years. Nobody has shown which interval prevents more fires, but a check is cheap compared with a burnt board. Ask for terminals to be retorqued and for a temperature check with the house’s big loads running. A thermal camera or infrared thermometer finds a hot terminal that looks fine.
• Get a check after any work on the meter, the board or the main cables, and straight away if flickering or trips start afterwards.
• Press the RCCB’s test button monthly. It proves the RCCB still trips on leakage. It says nothing about loose terminals.
• Use approved devices. MCBs, RCCBs and RCBOs need ST approval and the ST-SIRIM label. The enclosure itself isn’t on ST’s approved list. Plastic boards from Schneider’s Easy9 range and Hager’s golf range state that they pass the 650°C glow-wire test. Maxguard sells a separate fire-retardant PS line but prints no test temperature. Our DB box guide compares the boards sold in Malaysia.

Does the brand matter?

The burnt boards in these posts carried Maxguard, ABB, Hager, TBC and other brands. That mostly reflects what’s installed in Malaysian homes, not which brand fails. Some electricians said certain budget brands “tak tahan panas” (can’t take the heat), and others advised against mixing brands in one board. Neither claim was backed by more than opinion. In the cases with clear photos, the failure point was a connection. A better device helps, but a properly made joint matters more. Our MCB and RCCB brands guide covers what’s sold here.

If a repair turns into a whole new board, our DB box upgrade guide covers when that makes sense and what wiremen charge. Undersized or fake cable heats up too, so see SIRIM-labelled cable before buying replacement wire, and earthing and surge protection for lightning, a different way a DB gets damaged. Trips without heat or a smell are usually leakage, covered in RCCB keeps tripping.