Main Circuit Breaker (MCB)

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Understanding Main Circuit Breaker (MCB) & DB Box For HDB Flats


In Singapore, the electrical wiring configuration may differ for different HDB units.  But basically our main power supply enters our apartment via the Main Circuit Breaker (MCB), located next to our electricity meter outside our HDB unit.

This power then flows into our flat by feeding into an internal wiring cabinet called the Electrical Distribution Box or the DB Box (also known as the Fuse Box or the Circuit Breaker Panel).

The DB Box then splits up the power into many smaller circuits, which send power to various parts of your flat.

Each circuit is protected by an electrical circuit breaker or fuse.

Each circuit is allowed to transport a given amount of energy along its set of wires to the various electrical components/devices in our homes.

The main purpose of the MCB is to cut off the power supply to any HDB unit drawing too much power – thus reducing the chance of tripping the whole HDB block of flats!

So sometimes, if your home MCB is too old, a qualified electrician will recommend you replace your old worn out MCB with a new box. This is to ensure that your home will be always be protected by a working MCB and to prevent any fires!


Why Do Electricians Install Circuit Breakers – CBs, ELCBs, RCDs

There are a few different kinds of switches contained within the DB Box.

One of them is the Electric Circuit Breaker (CB), an electrical switch designed as a safety feature to protect an electrical circuit from damage caused by a power overload or a short circuit.  Its role is to break the circuit by interrupting current flow once a fault condition is detected.

Circuit breakers, like fuses, are rated by the current size they can conduct before they would trip.  Different ratings are needed for different kinds of devices.

Certain household appliances (eg. air conditioners, refrigerators, freezers) need a higher wattage (a lot more power) so they require circuit breakers of higher ratings, usually 20A.  Less power hungry devices like our televisions, lightings, computers can have circuit breakers of lower ratings, typically 10A or 16A.

Besides the circuit breakers, there is an earth leakage protection device – Earth Leakage Circuit Breaker (ELCB), or a newer type called the Residual Current Device (RCD).

These devices are tripped if they detect a small current imbalance between the Live and Neutral wires above the trip value (eg. 30mA).  RCDs protect a single or a number of circuits – so if one circuit trips, only that one circuit will be shut down, instead of the entire house.

An optional surge protector may also be installed to protect devices from power supply spikes, especially in areas with poor earthing and frequent lightning occurrences.

Why Do Our Circuit Breakers Trip?

The most common reasons our circuit breaker trips are as follows:

  1. Overloaded circuit – too many electrical appliances are plugged into the same circuit.
  2. Poor connections – electrical wiring has degraded over time.  Loose or corroded connections can cause increased resistance, which generates excess heat.
  3. Short circuit – live electrical wires overheat, melting the outer insulation, causing fires or electric arcs. Or a live wire touches a grounded or neutral wire or other unintended conductors.
  4. Defective electrical devices – these devices draw electricity in surges or they may draw excessive power, thus causing circuit breakers to trip.

Generally, all the above factors are inter-related in one way or another.

Leave The Dangerous Work To An Electrician

Because of the important role they play in protecting our homes’ electrical system from damages and ourselves from danger, it is of utmost importance that our circuit breakers, fuses, MCBs, RCDs are in tip top working condition at all times.

If you should encounter any sort of problem with your circuit breaker or other protective devices, an experienced electrician should be consulted.

So if you need professional help with your MCB, DB Box or circuit breaker repair, replacement or upgrades, feel free to call us at 9729 1059 or book an appointment with us now!

Call 65 9729 1059 for FAST Plumbing & Electrical Services!