Breakers · Guide

RCCB, ELCB and MCB Explained for Singapore Homes

Open distribution board with rows of breakers

In one line: an MCB protects the circuit from too much current (overload and short circuit); an RCCB protects you from current leaking to earth (electric shock); and an ELCB is the older version of the RCCB. A modern DB box uses an RCCB plus one MCB per circuit, different guards for different dangers.

What each device actually does

MCB, Miniature Circuit Breaker. One sits on each circuit in your DB box. Its job is current: if a circuit draws more than it should, the classic overloaded kitchen, or a short circuit, the MCB cuts that circuit before the cable overheats. It protects the wiring.

RCCB, Residual Current Circuit Breaker. This one watches for imbalance: it compares the current flowing out against the current coming back, and if some is “leaking” to earth, through a faulty appliance, damp, or a person, it trips in a fraction of a second. It protects people from shock. This is the device that saves lives.

ELCB, Earth Leakage Circuit Breaker. The older technology the RCCB replaced. Early ELCBs were voltage-operated; the RCCB is current-operated and more reliable at catching leakage. If your board still has an ELCB, it is worth an electrician’s assessment.

Which one trips in which situation

Overload three appliances onto one circuit and the MCB for that circuit trips, the rest of your flat stays on. Get earth leakage, an appliance fault, water in an outdoor point after rain, and the RCCB trips, which because it sits upstream can take several circuits dark at once. So a rough diagnosis: one room or circuit dead usually means an MCB; half the flat dead after rain usually means the RCCB. Our power trip guide walks through what to do next.

The test-button habit

Your RCCB has a small “T” (test) button. Pressing it about once a month should make the RCCB trip instantly, proof it will still act if a real fault occurs. If it does not trip on test, the device has likely failed and needs replacing, even though your power is on. It is thirty seconds a month that verifies your main shock protection is alive.

When replacement is due

Protective devices age. Signs it is time to look: an RCCB that nuisance-trips with no traceable cause, one that will not trip on the test button, a very old ELCB, or a board so full that new circuits have nowhere to go. Replacement is straightforward licensed work inside the DB box, never a DIY job, since it sits on the live side of your supply.

RCCB, ELCB and MCB questions

Are MCB and RCCB the same?

No. An MCB (Miniature Circuit Breaker) protects against overload and short circuit, too much current on a circuit. An RCCB (Residual Current Circuit Breaker) protects against current leaking to earth, which is the shock and electrocution risk. They guard against different dangers, which is why a modern DB box has both.

Which comes first, MCB or RCCB?

In a typical consumer unit the RCCB sits upstream, protecting a group of circuits, and the individual MCBs sit downstream on each circuit. So power flows main switch → RCCB → MCBs → your circuits. This is why a single earth-leakage fault on one circuit can trip the RCCB and take out several circuits at once.

Which is safer, RCCB or ELCB?

The RCCB is the modern standard and is considered more reliable. ELCB (Earth Leakage Circuit Breaker) is the older voltage-operated technology; RCCB is current-operated and detects leakage more dependably. If your DB still uses an old ELCB, it is worth having an electrician assess whether it should be upgraded.

Can I use an RCCB without an MCB?

You should not rely on one alone, they do different jobs. An RCCB will not trip on a simple overload, and a plain MCB will not protect you from an earth-leakage shock. Modern installations use both, either as separate devices or combined in an RCBO. An electrician sizes them to your circuits.

What is an RCBO?

An RCBO combines both functions in one device, overload and short-circuit protection like an MCB, plus earth-leakage protection like an RCCB, on a single circuit. Using RCBOs means an earth fault on one circuit only trips that circuit, rather than a shared RCCB knocking out several at once.

How often should I test my RCCB?

The common guidance is to press the test button on the RCCB about once a month. It should trip instantly; if it does not, the device may have failed and needs an electrician to check or replace it. A device that will not trip on test is not protecting you, even though the power is on.

Why does my RCCB keep tripping?

Usually genuine earth leakage, a faulty appliance, water ingress after rain, or ageing wiring, the RCCB doing exactly its job. Occasionally the RCCB itself is worn and nuisance-tripping. Because a tripping RCCB signals a real shock-risk fault, repeated tripping is worth diagnosing rather than resetting.