Short answer: an MCB protects a circuit from too much current, from an overload or a short circuit. An RCCB protects people from electric shock by tripping when current leaks to earth. An MCCB does the same job as an MCB but for much larger currents, which is why it usually sits at the main supply of a large house or building. Most homes use MCBs on their individual circuits and residual-current protection on at least some of them. Which devices and ratings your home needs is a decision for a qualified electrician.
What each device does
MCB: miniature circuit breaker
An MCB switches a circuit off when the current through it is too high. It has two tripping mechanisms: a thermal part that reacts to a smaller overload that lasts for a while, and a magnetic part that reacts almost instantly to the very large current of a short circuit. MCBs protect the individual circuits in a distribution board, such as a lighting circuit or a socket circuit, and they cover currents up to about 100 to 125 A.
RCCB: residual current circuit breaker
An RCCB compares the current going out along a circuit with the current coming back. If some of it is leaking away, for example through a damaged appliance or through a person, the difference is the residual current, and the RCCB trips. Devices intended to protect people commonly trip at 30 mA, fast enough to reduce the risk of a fatal shock. An RCCB does not protect against overload or short circuit, so it is always used together with MCBs or another overcurrent device.
MCCB: moulded case circuit breaker
An MCCB protects against overload and short circuit like an MCB, but it is built for much higher currents, from tens of amps up to thousands. Many MCCBs have adjustable trip settings, while an MCB’s trip points are fixed at the factory. MCCBs are typically used as the main incoming breaker or on large sub-boards, more often in large houses, apartment buildings and commercial premises than on ordinary household circuits.
RCBO and ELCB
An RCBO combines an MCB and an RCCB in one device, so a single circuit gets both overcurrent and earth-leakage protection. ELCB is an older name you may still hear; the original voltage-operated ELCBs have largely been replaced by current-operated residual current devices such as RCCBs and RCBOs.
MCB vs RCCB vs MCCB compared
| Device | Protects against | Typical ratings | Where it is used |
|---|---|---|---|
| MCB | Overload and short circuit | Up to about 100 to 125 A, fixed trip settings | Individual circuits in a home’s distribution board |
| RCCB | Earth leakage, to reduce the risk of electric shock | Commonly 30 mA trip sensitivity for protecting people | Groups of circuits, together with MCBs |
| MCCB | Overload and short circuit at higher currents | From tens of amps up to thousands, often adjustable | Main incoming supply, large boards, commercial buildings |
| RCBO | Overload, short circuit and earth leakage | Combines MCB and RCCB ratings in one device | Individual circuits that need both kinds of protection |
Ratings, trip curves and poles in plain terms
Rated current
Every breaker has a rated current, written as a number of amps, for example 16 A or 32 A. It is the current the breaker carries continuously without tripping. An electrician matches the rating to the circuit it protects, so that the breaker trips before the circuit is overloaded.
Trip curves: B, C and D
On MCBs, the letter in front of the rating (such as C16) is the trip curve. It sets how large a sudden surge of current must be before the breaker trips instantly:
- B curve: trips at about 3 to 5 times the rated current. Used for circuits with small start-up surges, such as many lighting and general household circuits.
- C curve: trips at about 5 to 10 times the rated current. Used where equipment draws a moderate surge when it starts, such as motors and some lighting.
- D curve: trips at about 10 to 20 times the rated current. Used for equipment with heavy start-up surges, more common in commercial and industrial settings.
Poles
The number of poles is how many conductors the device switches. Single-pole and two-pole devices are used on single-phase circuits; three-pole and four-pole devices are used on three-phase supplies. In Pakistan, household supplies are normally single-phase at 230 V and 50 Hz, while larger homes and buildings may have a three-phase supply at 400 V.
Where each one is typically used in a home
- Individual circuits: an MCB, or an RCBO, on each lighting, socket and appliance circuit.
- Shock protection: an RCCB protecting a group of circuits, or RCBOs on individual circuits. Many wiring standards require residual-current protection for socket circuits and for circuits in wet areas such as bathrooms.
- Main incoming supply: a main breaker sized for the whole house; in larger homes and buildings this is often an MCCB.
Every installation is different, and the right combination depends on the supply, the size of the house and the circuits in it.
Have a qualified electrician choose and fit breakers
Circuit breakers are part of your home’s mains wiring. Choosing the right type, rating, curve and number of poles, and fitting them in the distribution board, must be done by a qualified electrician. This guide is general background only and is not installation advice.
If a breaker trips repeatedly, treat it as a sign of a fault or an overloaded circuit and ask an electrician to find the cause.
Frequently asked questions
What is the difference between an MCB and an RCCB?
An MCB trips when there is too much current in a circuit, from an overload or a short circuit. An RCCB trips when current leaks to earth, to reduce the risk of electric shock. They protect against different faults, so they are used together.
Do I need an RCCB if I already have MCBs?
MCBs alone do not detect a small leakage current through a person, so they do not give shock protection. Residual-current protection from an RCCB or RCBOs adds that. A qualified electrician can tell you which circuits in your home need it.
What is the difference between an MCB and an MCCB?
Both protect against overload and short circuit. An MCB covers currents up to about 100 to 125 A and has fixed trip settings; an MCCB covers much higher currents and often has adjustable trip settings, so it is used for main supplies and large boards.
What do B, C and D mean on an MCB?
They are trip curves. A B-curve MCB trips instantly at about 3 to 5 times its rated current, a C curve at about 5 to 10 times and a D curve at about 10 to 20 times, to suit circuits with small, moderate or heavy start-up surges.
What is an RCBO?
An RCBO combines an MCB and an RCCB in one device, so a single circuit is protected against overload, short circuit and earth leakage.
Who should choose and fit a circuit breaker?
A qualified electrician. Breakers are part of the mains wiring, and the type, rating, curve and number of poles have to be matched to your supply and circuits.
Planning a smart home?
Breakers protect the circuits; smart switches, touch panels and door locks are what you use every day. Browse our smart switches, read our smart door lock guide or control panel comparison, or ask us on WhatsApp about home automation for your home.
