Do you need to replace your DB box? What Malaysian wiremen say, what it costs and what to check

“Your DB box is outdated, it has to be changed first.” Homeowners hear this from aircond installers, renovators and new-house inspectors, and then ask the electrical groups whether it’s true. The wiremen’s answers are more careful than the contractor pages that come up on Google: sometimes the whole board does need replacing, but often the job is one new circuit or a couple of breakers.

Adding an aircond often doesn’t need a new DB

In one widely-read Pendawai Elektrik thread, an aircond installer told the owner of a 20-year-old house to replace the DB before adding a fifth unit. The owner posted a photo. Most wiremen who replied said the board was already three-phase and looked usable. Their advice:

• check whether the existing main switch, RCCB and breakers still work properly, and replace any that are worn;
• add an MCB for the new aircond if there’s a free slot;
• run a dedicated circuit from the DB to the aircond, not a connection looped from a nearby socket.

Several said a full DB replacement for one aircond looked like overcharging. One pointed out that if the board really were obsolete, the wiring behind it would be too, so the advice didn’t add up.

Not everyone agreed. Others in the same thread said a board without enough ways has to be upgraded anyway, that boards older than about 15 years are better replaced, and that a board with a lot of looped wiring is worth redoing. A photo of the cover can’t settle it; someone has to open the board and check its condition and free ways. If it has no free slots, a small second DB is a common alternative to replacing the main one.

An aircond does need its own properly sized circuit. The Energy Commission’s (ST) guideline lists 4–6mm² cable for special power circuits such as aircond; our aircond guide covers the circuit in detail.

When an upgrade is worth it

The case for a new or bigger board is stronger when:

• there are no spare slots and you’re adding circuits;
• lighting and sockets share one RCCB, so a leak anywhere cuts everything;
• water heaters have no 10mA protection of their own;
• the components are old pull-out fuse types, damaged or overheating;
• you’re moving into a house and can do everything at once.

For a house about to be occupied, with three 1hp aircond, one 3hp unit and two water heaters, the commonly suggested changes were:

• a board with spare ways for future circuits (how to size a DB box);
• separate RCCBs for lighting and for sockets;
• an RCBO or RCCB for each water heater. ST’s water heater guideline requires 10mA sensitivity, and in another thread members corrected a widely-liked answer that claimed 30mA was enough (water heater guide);
• each aircond on its own MCB, with the larger unit on a bigger breaker.

One reply also suggested fitting an SPD and checking the earth reading while the board is open. ST’s guideline makes an SPD depend on a lightning risk assessment rather than fitting one by default (earthing guide). One commenter suggested converting to three-phase, and another replied that single-phase was enough and the conversion would waste money. Our single vs three-phase guide covers that decision.

What ST’s guideline says about the board

The Energy Commission’s domestic wiring guideline sets out a few points worth knowing before you get a quote:

• The DB should follow the MS IEC 60670 standard, with the main switch at a height an adult can easily reach.
• An RCCB’s current rating must be at least that of the nearest breaker upstream. For example, a 40A RCCB fed directly from a 63A breaker doesn’t meet it.
• If a main RCCB has a time delay, it must be 500 ms or less.
• The main circuit cable must be at least 10mm² for a main breaker rated up to 40A, 16mm² up to 63A and 25mm² up to 100A.
• Installations above 100A must be designed by a registered consulting engineer or an ST-registered electrical contractor.

Inside the board, the order is incoming supply, then main switch, then RCCBs, then MCBs. Asked whether one layout photo was “correct” and another “wrong”, wiremen said both were fine. Left or right placement depends on which side the supply cable comes in, and on keeping the cables short and tidy. When another photo was posted later in the thread, one or two members called out its unmarked cables and a 300mA RCCB in a house.

Choosing the new board

If the board does need replacing, the box itself is a choice too. Count the modules the new devices take and add spare ways. In our worked example, a single-phase terrace house with two RCCB groups, two water heaters and a dozen MCBs needs about 22–26 modules, so a board of 36–39 modules leaves room. Ask for separate neutral bars for each RCCB group. A steel (“metalclad”, “DB besi”) board must be earthed; a plastic one stated as class II (double insulated) doesn’t need to be, and for plastic a fire-retardant type is worth asking for. Our DB box guide covers sizing, metal versus plastic and the ready-to-use sets, and compares the boards on Malaysian lists:

• Maxguard: metalclad DB-E and DB-N boxes from about RM137 to RM440 on Shopee, plastic MG units, and ready-to-use boards with the incomer and RCCB fitted;
• Hager IU steel boards (IU39S, three rows of 13, about RM354–441) and Hager golf plastic boards, flush or surface;
• Schneider Resi9 MP plastic boxes up to 36 modules surface-mounted, and the larger PrismaSeT XS.

Ready-to-use boards and marketplace “full sets” usually come with one 100mA RCCB (300mA on three-phase). A 300mA device doesn’t meet the 100mA limit for lighting and aircond circuits, so those need a 100mA RCCB, socket circuits 30mA and water heaters 10mA.

“My sockets use C32 breakers. Is that dangerous?”

It depends on the circuit. For general socket circuits, ST’s guideline allows a 32A breaker on a ring circuit of 2.5mm² cable (serving up to 100m² of floor area) or on a radial circuit of 4mm² (up to 75m²). A radial circuit on 2.5mm² should have a 20A breaker (up to 50m²). So a second electrician who swaps a C32 for a C20 might be right or might be unnecessary. Ask whether the circuit is a ring or a radial and what size the cable is. Our cable guide explains the sizes.

The same thread mixed up what each device does. An MCB trips on overload or on a short between live and neutral, while an RCCB trips when current leaks to earth; a severe live-to-earth fault may trip both. Because they cover different faults, a board needs both, or RCBOs that combine them.

Damaged cables at the board

If you can see bare copper where cables enter the main switch or breakers, don’t leave it. Wiremen recommended cutting back or replacing the damaged cable and terminating it properly, and warned that exposed copper can cause tracking and trips. Some members suggested taping or heat-shrinking it; treat that as a stop-gap until a proper repair.

Main cables are large, typically 10mm² or more. If the damage is on the incoming cables, before the main switch, turning the main switch off doesn’t make them dead; they have to be isolated at the meter side. This is work for a competent wireman.

What it costs

Prices from the groups in 2025–2026. These are individual quotes and estimates, not market rates:

Contractor sites list RM300–1,500 for a single-phase DB installation depending on state, and RM850–1,300 including parts, with about RM200 more for a metal-clad box. Get a written list of what’s being replaced: the box (brand, code and number of ways), main switch, how many RCCBs and of what sensitivity, how many MCBs and RCBOs, and whether an SPD is included. Ask for a workmanship warranty too. One wireman offered only a month on a replacement board because he couldn’t vouch for the old wiring behind it, which is a fair caveat to ask about.

For other electrical work prices, see our house wiring prices guide; for choosing breaker brands, see MCB and RCCB brands.