What do the switches in your DB box do?

What is inside your DB box

HDB's guide to electrical accessories and wiring calls this panel the consumer unit, which distributes electricity in your flat. It holds double pole MCBs (one of them is the main switch), an RCCB, single pole MCBs and terminals.

In its electrical safety advice, the Energy Market Authority (EMA) writes this switch as RCCB (or ELCB). Here is your distribution board explained, switch by switch.

Main switch ratings on the label

The rating is printed on your main switch. HDB's renovation guidelines for electrical works say flats in blocks completed since 1994, or upgraded under the Main Upgrading Programme (MUP) or Home Improvement Programme (HIP), have a 40amps main switch. Older flats have a 30amps main switch.

The rating matters when you add appliances. HDB requires a permit for a new 15amps power point or a 20amps isolator for the aircon in flats with a 30amps main switch. Flats with a 40amps main switch, or upgraded under MUP or HIP, need no permit for these.

Label your circuits

If your DB box labels are missing, faded or wrong, you can work them out yourself. This is practical guidance, not an official rule.

• Check that your hands, the floor and the DB box are dry before you start.
• Switch off one MCB at a time and note which lights and sockets go off.
• Switch that MCB back on before you move to the next one.
• Write a short, clear label next to each MCB, such as "kitchen sockets" or "bedroom lights".

Never open the DB box cover or touch anything behind it. For other checks around the flat, see our home electrical safety checklist.

Test the RCCB once a month

EMA says to test the RCCB once a month. HDB gives the same tip and asks you to switch off sensitive equipment, such as computers, before the test.

1. Switch off sensitive equipment. Turn off computers and similar equipment first. Make sure your hands and the DB box are dry.
2. Press the test button. Press the button marked T on the RCCB once.
3. Check that it switches off. The RCCB should switch off and cut power. If it does not, it may be defective, so call a Licensed Electrician.
4. Switch it back on. Push the RCCB back up to restore power, then turn your equipment back on.

Resetting a trip safely

The next steps are practical guidance, not an official rule. When the DB box is dry and nothing smells burnt, switch off or unplug what was running when the power went, then push the tripped switch back up once. If it trips again straight away, leave it off and call a Licensed Electrician. Do not keep resetting it.

An RCCB trip means it detected current leakage. EMA lists ageing or exposed wires, faulty electrical appliances and damaged insulation as causes of leakage.

If this keeps happening, read our guide for when your ELCB keeps tripping.

If the whole flat has lost power, start with our guide to no power in the whole flat.

When to call a Licensed Electrician

EMA's guide to engaging licensed workers says electrical work at home should be carried out or supervised by a Licensed Electrical Worker (LEW). EMA says electrical work in an HDB flat needs a Licensed Electrician, the class of LEW approved for loads of up to 45kVA. EMA lists repair or replacement of consumer control units or circuit breakers as LEW work, so replacing a DB box, an RCCB or MCBs is a job for a Licensed Electrician. Check the worker's licence card before any work starts, or search EMA's ELISE portal.

Our guide to what work needs an LEW covers other jobs around the flat.

EMA's electrical safety rules require every home to have an RCCB (or ELCB) rated at 30mA or less. HDB flats built before 1985 did not come with one unless the owner added it later. If yours has none, engage an LEW to install it.

For DB box replacement, 5 companies publish a DB box line, and the 4 that price it per job have lowest published rates from S$280 to S$320 per job, as printed, to replace or upgrade the DB box.

FROM THE HOMEZYPRO DIRECTORY

Published DB box replacement rates

For the most common unit (per job), the lowest published DB box replacement rates from 4 companies run from S$280 to S$320 per job, to replace or upgrade the DB box. Each figure is one company's own advertised rate with its conditions, not a quote.

See 5 published DB box replacement rates and sources

Lowest matching advertised rate per company, in SGD as published. "From" marks a starting price and ranges are shown in full. Check the source for minimums, GST and inclusions.

Company	Service as listed	Rate	Source
SC Electrician	Main Distribution Board (DB Box) Replacement	S$280 to S$480 per job	scelectrician.sg
Electrician24 Singapore	DB Box Upgrade	S$300 to S$600 per job	electrician24.sg
Lito Electrical Service	DB box replacement 2 ROOM	From S$320 per job	litoelectrical.com
Repair.sg	Distribution board supply and install	From S$320 per job	repair.sg
Mr Electrician Pte Ltd	MCB & DB Box SP 40A 18P	S$450	mrelectrician.sg

Ask each company what its price covers, and see electrician costs for other electrical jobs.

Questions