How MCBs, MCCBs, ACBs, RCCBs and RCBOs differ, which IEC standard each follows, what trip curves and breaking capacities mean, and which breaker goes where in a Gulf installation.
Low-voltage circuit breakers come in five types. MCBs protect final circuits up to 125 A. MCCBs cover feeders from about 100 A to a few thousand amps. ACBs serve main incomers up to 6,300 A. RCCBs detect earth leakage only, and RCBOs add overcurrent protection to the same device. Choose by the standard, the trip curve, the breaking capacity at the point of installation and the ambient temperature. Then shortlist circuit breaker suppliers in the UAE against those four points.
This guide is for designers, MEP contractors and maintenance engineers who specify, approve or replace breakers. It covers the standard behind each type, B, C and D curves, Icu and Ics, selectivity and residual current types. For the switchboards, panel brands and approvals that these breakers sit inside, see our guide to switchgear and panel brands in the UAE and Saudi Arabia. Buyers in the Kingdom can compare circuit breaker suppliers in Saudi Arabia.
The product standard each type is built to fixes its rating limits and test method.
| Type | What it does | Product standard (current edition) | Scope limits in the standard | Typical place in the system |
|---|---|---|---|---|
| MCB (miniature circuit breaker) | Overload and short-circuit protection, fixed setting | IEC 60898-1:2015+AMD1:2019 (household and similar); many MCBs are also certified to IEC 60947-2 | Up to 440 V AC between phases, 125 A, 25,000 A short-circuit capacity | Final circuits in distribution boards |
| MCCB (moulded case circuit breaker) | Overload and short-circuit protection, usually adjustable | IEC 60947-2:2024 | Up to 1,000 V AC or 1,500 V DC, for instructed or skilled persons | Sub-main feeders, motor and equipment feeders, small incomers |
| ACB (air circuit breaker) | Incomer, bus coupler and large feeder protection, with electronic trip unit | IEC 60947-2:2024 | As for MCCBs | Main LV switchboards |
| RCCB (residual current circuit breaker) | Trips on earth leakage only; no overcurrent protection | IEC 61008-1:2024 | Up to 440 V AC, 125 A | Upstream of a group of MCBs |
| RCBO (RCD with overcurrent protection) | Earth leakage plus overload and short-circuit protection in one device | IEC 61009-1:2024 | Up to 440 V AC, 125 A, 25,000 A short-circuit capacity | Individual final circuits |
IEC 60898-1 itself excludes breakers that protect motors, breakers whose current setting the user can adjust, DC breakers and breakers with residual current tripping (covered by IEC 61009). Anything outside those limits falls under IEC 60947-2, which is why MCCBs and ACBs are built to it.
Note the recent revisions: IEC 60947-2 reached its sixth edition in September 2024 (replacing 2016 plus its 2019 amendment), and IEC 61008-1 and IEC 61009-1 their fourth editions in November 2024 (replacing the 2010 editions and amendments). Specifications quoting older editions should be updated.
An MCB has two trip elements. A thermal element, usually a bimetal strip, responds slowly to overloads. A magnetic element trips within milliseconds when the current passes a set multiple of the rated current (In). The letter on the breaker tells you that magnetic threshold. ABB's technical article on trip curves gives the bands:
The standard sets only the limits of each band; the manufacturer decides where within it the product trips. Two practical points follow. First, ABB notes that a fast B curve can see motor or transformer inrush as a fault, so the fix for tripping on switch-on is often a C or D curve rather than a larger rating. Second, a D-curve breaker may need up to 20 times its rating to trip instantly, against up to 5 times for a B curve, so changing B to D on an existing circuit is a design change: the designer must confirm the fault current at the end of the cable is still high enough, not treat it as a like-for-like swap.
Schneider Electric's FAQ on its Acti9 iC60 range sets out the two sets of conventional currents. Under IEC 60898-1 the breaker must not trip at 1.13 times In and must trip at 1.45 times In within the conventional time of one hour, tested at a 30 °C reference temperature. Under IEC 60947-2 the figures are 1.05 and 1.30 times In, and the manufacturer sets the reference temperature. Schneider gives 50 °C as the reference for its MCBs certified to both standards and 40 °C for those certified to IEC 60947-2 only, and notes that the reference temperature for the rated current must be printed on the device.
This matters in the Gulf, where the air inside a board in a plant room or outdoor kiosk can be well above 30 °C. A breaker carries less than its nameplate current above its reference temperature, so it can trip on load on a hot afternoon. Ask the supplier which reference temperature the offered MCB is calibrated at, and use the manufacturer's derating table for the temperature inside the enclosure, not the room.
Above 125 A, or wherever you need adjustable settings, you move to IEC 60947-2 devices. Schneider Electric's UAE site lists its ComPacT MCCBs from 100 A to 3,200 A and its MasterPact ACBs up to 6,300 A. Hager lists hw+ ACBs for projects up to 6,000 A. Mitsubishi Electric groups its range into ACBs, MCCBs, ELCBs and MCBs.
The trip unit is what you are really specifying. Thermal-magnetic units have a fixed or limited adjustment. Electronic trip units let the engineer set separate functions, and ABB's selectivity paper refers to them by letter: L (protection against overload), S (protection against delayed short-circuit) and I (instantaneous short-circuit protection). If the coordination study needs a short-time delay on a feeder so that downstream devices clear first, the breaker must have the S function; an MCCB with only L and I settings cannot provide it.
Breaking capacity varies with voltage. The 630 A breaker in the photo above, for example, lists an Icu of 36 kA at 400/415 V and 20 kA at 690 V on its plate. Always read the column for your system voltage.
Selectivity means that when a fault occurs, only the breaker nearest to it opens and the rest of the installation stays energised. ABB's technical paper on LV selectivity quotes the IEC 60947-2 definitions:
The same paper describes the techniques. Time-current selectivity makes the upstream breaker trip slower than the downstream one across the overload range. Current selectivity uses different instantaneous thresholds and is often only partial unless a transformer or long cable sits between the two breakers. Time selectivity uses the delayed short-circuit function (S): the upstream breaker waits long enough for the downstream one to clear the fault. ABB notes that with the upstream ACB's instantaneous function switched off, the selectivity limit equals that ACB's Icw. Energy selectivity relies on the maker's tested tables. Zone selectivity uses a signal wire or bus between trip units so that only the breaker immediately upstream of the fault trips.
Each manufacturer publishes coordination tables for its own breaker combinations, so mixing brands between an incomer and its feeders can leave you without published values. Ask for the tables or a coordination study covering every breaker pair.
A residual current device compares line and neutral currents; if some current leaks to earth, the imbalance trips it. An RCCB does only this; it needs an MCB or fuse upstream or downstream for overcurrent protection. An RCBO combines the RCD and the MCB, so each circuit trips on its own and a fault on one does not take out a whole group.
Schneider Electric's guidance on choosing RCCB sensitivity gives 30 mA for protection against electric shock by direct contact and 300 mA for protection against fire due to leakage current. Where 30 mA protection is mandatory is set by the wiring regulations your utility applies and the consultant's specification.
The type letter describes which current waveforms the device will detect.
| Type | Detects | Standard |
|---|---|---|
| AC | Sinusoidal AC residual current | IEC 61008-1 or IEC 61009-1 |
| A | Sinusoidal AC plus pulsating DC residual current | IEC 61008-1 or IEC 61009-1 |
| F | As type A, plus composite residual currents, for installations supplied through frequency inverters | IEC 62423 with IEC 61008-1 or IEC 61009-1 |
| B | Alternating sinusoidal residual currents up to 1,000 Hz, plus pulsating and smooth DC residual currents | IEC 62423 with IEC 61008-1 or IEC 61009-1 |
Type F and type B requirements are set out in IEC 62423:2009, which applies in addition to IEC 61008-1 and IEC 61009-1 rather than replacing them. A type AC device is only defined for sinusoidal AC leakage, so match the type to the load and follow the equipment maker's instructions on which RCD type it needs.
The term ELCB covers two different things. Historically it meant a voltage-operated earth leakage breaker that sensed a rise in voltage on metalwork relative to a separate earth electrode. Those devices largely fell out of favour after current-sensing RCDs arrived. They can only detect faults on metalwork connected to them, and a broken wire in the fault-to-load section disables them. Today, many manufacturers use "ELCB" for a current-operated breaker with earth leakage protection; Mitsubishi Electric, for example, lists ELCBs that provide overload, short-circuit and earth-leakage protection. When a drawing says ELCB, ask the designer to state the product standard, sensitivity and type letter.
All of these brands list full LV breaker ranges; compare them on rating, curve, breaking capacity and selectivity data, not on name. Schneider Electric lists ComPacT MCCBs from 100 A to 3,200 A, MasterPact ACBs up to 6,300 A and the dual-rated Acti9 iC60 MCB family. ABB publishes trip curve guidance and coordination tables between its moulded case and miniature breakers. Hager lists MCBs, RCCBs, RCBOs, MCCBs and hw+ ACBs up to 6,000 A in its Middle East catalogue. Mitsubishi Electric lists ACBs, MCCBs, ELCBs and MCBs, with RCCBs and RCBOs in its MCB family. For Eaton, Legrand, Siemens, LS Electric, Chint and others, the main switchgear guide sets out what each group makes.
UAE: MoIAT regulates low-voltage electrical products; confirm with the supplier and certifying body whether your breakers are in scope, and see our guide to ECAS and EQM product conformity. The utility's wiring regulations and your consultant's specification decide where RCD protection is required and at what sensitivity, so check them before you fix the board schedule.
Saudi Arabia: imported breakers go through SABER under SASO technical regulations, as the main guide explains. For SEC-connected projects or a client's plant, check the approved manufacturer list, which can fix the brand, standard and breaking capacity. LV switchgear suppliers in Saudi Arabia can usually supply the breakers and boards together.
Send that list with the single-line diagram and you can post a requirement on ListGCC for breaker suppliers in the UAE and Saudi Arabia to quote.
More in this series: LV vs MV Switchgear, and Gas-Insulated vs Air-Insulated Explained, Motor Control Centres (MCC), Type-Tested Switchboards and Licensed Panel Builders in the UAE and Saudi Arabia, Distribution Boards.
The letter sets the magnetic trip threshold. ABB's technical article gives B as 3 to 5 times rated current, C as 5 to 10 times, and D as 10 to 20 times. ABB describes C as suited to medium inrush currents and D to high starting currents, such as transformers and motors. A higher curve needs a higher fault current to trip instantly, so check it against the circuit design.
If ELCB means the old voltage-operated device, an RCCB is the better choice, because it senses any current leaking to earth rather than only voltage on connected metalwork. Many manufacturers now use ELCB for current-operated earth leakage breakers, which work like RCCBs or RCBOs. Ask for the standard, sensitivity and type letter so you know which device is being offered.
Icu is the rated ultimate short-circuit breaking capacity: the highest fault current the breaker can interrupt. Ics is the rated service breaking capacity: the fault current it can interrupt and still remain in service, stated as 25, 50, 75 or 100% of Icu under IEC 60947-2. Both must be read at your system voltage. Where downtime is costly, ask for Ics equal to Icu.
Often, yes. IEC 60898-1 tests MCBs at a 30 °C reference temperature, and IEC 60947-2 lets the manufacturer set its own reference, such as 40 or 50 °C. Inside a hot enclosure the breaker carries less than its nameplate current and may trip on load. Ask for the reference temperature and use the manufacturer's derating table for the temperature inside the board.
IEC 62423 defines two types for these circuits. Type F is for installations supplied through frequency inverters and adds composite residual currents to type A. Type B goes further, detecting AC residual currents up to 1,000 Hz and smooth DC as well as pulsating DC. Type AC is only defined for sinusoidal leakage. Confirm the required type in the drive manufacturer's installation instructions.
Featured image: Photo: Santeri Viinamäki, CC BY-SA 4.0, via Wikimedia Commons
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