IEC 60947-2 Standards for Molded Case Circuit Breakers Explained

IEC 60947-2 is the international standard for low-voltage circuit breakers up to 1000 V AC / 1500 V DC, defining Icu, Ics, Icw, utilization categories, and type tests engineers must verify to avoid coordination failures and FAT rejection.

Published: 2026-05-06 | Last updated: 2026-05-06 | By Stoklink Engineering Team

If you have ever opened a project specification from a German EPC contractor and seen a phrase like "MCCB shall comply with IEC 60947-2, utilization category B, Icu = Ics = 50 kA at 415 V AC", you already know that the standard is more than a stamp on a datasheet. It is the contractual language that defines how the breaker must behave when a fault occurs, and how the manufacturer must prove it. In our experience working with substations across the Middle East, Europe and Southeast Asia, roughly 30% of MCCB-related disputes during commissioning trace back to a misreading of one or two clauses in this document.

Scope and Structure of IEC 60947-2

IEC 60947-2 is part 2 of the IEC 60947 family, which collectively covers low-voltage switchgear and controlgear. Part 1 establishes general rules. Part 2 applies specifically to circuit breakers — including MCCBs, miniature MCCBs in the upper frame range, and air circuit breakers (ACBs) when not separately governed by 60947-3 or 60947-4. The current edition, 5.2, consolidates amendments published over the last decade and is harmonized as EN 60947-2 in Europe.

The standard applies to breakers whose main contacts are intended to be connected to circuits with a rated voltage not exceeding 1000 V AC or 1500 V DC. This is a critical detail. For DC traction or photovoltaic systems above 1500 V, IEC 60947-2 alone is not sufficient — IEC 60947-2 Annex U (for direct current applications) and supplementary standards apply. Engineers often overlook this when specifying breakers for utility-scale solar combiner panels.

The document is organized into eight clauses plus annexes. Clause 4 covers classification. Clause 5 defines characteristics. Clause 7 specifies constructional and performance requirements. Clause 8 — the one most often cited in tenders — defines the type tests. Annex B addresses circuit breakers with electronic overcurrent protection, Annex F covers additional requirements for breakers with integrated current measurement, and Annex H deals with electromagnetic compatibility.

Why Part 2 Matters More Than Part 1

A common mistake during procurement is to cite "IEC 60947 compliant" without specifying the part. IEC 60947-1 covers general rules and is referenced inside Part 2, but on its own it does not certify a breaker. A datasheet that lists only "IEC 60947-1" without Part 2 is not making a meaningful protection claim. We have seen this in Chinese-export low-cost MCCBs where the marking is technically true but commercially misleading.

The full text and scope of IEC 60947-2 are published by the International Electrotechnical Commission and can be reviewed on the official IEC 60947-2 standard webstore page.

Key Ratings Defined in IEC 60947-2

The standard defines several rated values that every engineer must understand before selecting a breaker. These are not interchangeable, and confusion between them is the single most frequent cause of selection errors we see in the field.

Rated Operational Voltage (Ue) and Rated Insulation Voltage (Ui)

Ue is the voltage at which the breaker is intended to operate continuously. Ui is the maximum voltage the insulation system has been tested to withstand. For an ABB Tmax XT series breaker, Ui is typically 800 V while Ue is 690 V AC. Why the difference? Because temporary overvoltages from utility switching events can briefly exceed Ue, and Ui provides the dielectric margin defined under Clause 8.3.3.4 (impulse withstand test at 8 kV for 690 V class).

Rated Ultimate Short-Circuit Breaking Capacity (Icu)

Icu is the maximum prospective short-circuit current the breaker can interrupt without damage that prevents future operation, but the breaker is not necessarily required to remain in service afterwards. The test sequence per Clause 8.3.5 is O – t – CO, meaning the breaker performs one opening operation, waits the standard time interval, then performs a close-open cycle on the same fault current.

Rated Service Short-Circuit Breaking Capacity (Ics)

Ics is the breaking capacity the breaker can interrupt and remain operational. The test sequence is O – t – CO – t – CO. After the test, the breaker must still carry rated current and operate normally. Ics is expressed as a percentage of Icu — typically 50%, 75% or 100%. For mission-critical applications such as data center main feeders, we always specify Ics = 100% Icu, and we cover the rationale in MCCB selection for critical data center power systems.

Rated Short-Time Withstand Current (Icw)

Icw is the RMS current the breaker can carry for a defined short time (usually 1 second, sometimes 3 seconds) without tripping. This applies only to Category B breakers (see below) and is the critical parameter for time-based selectivity. A breaker with Icw = 50 kA / 1 s can wait for a downstream device to clear a fault before tripping itself. A detailed treatment of Icu, Ics and Icw ratings goes deeper into the test waveforms.

Utilization Categories A and B

Clause 4.4 of IEC 60947-2 splits MCCBs into two utilization categories. The distinction governs whether the breaker is suitable for time-graded selectivity and is one of the most important specification points for industrial distribution boards.

Category A breakers are not specifically intended for selectivity under short-circuit conditions with respect to other downstream protective devices on the load side. They have no specified Icw. ABB Tmax XT1, XT2, and similar compact frames typically fall here.

Category B breakers are specifically intended for selectivity under short-circuit conditions with respect to other short-circuit protective devices in series on the load side. They have a specified Icw and an intentional short-time delay. ABB Emax 2 (E1.2 through E6.2) and Tmax XT5 / XT7 with electronic trip units typically qualify. The ABB 1SDA070874R1 E1.2C 1600 Ekip Touch LI is a Category B breaker with Icw = 50 kA / 1 s, designed precisely for incomer duty in a switchboard where downstream MCCBs must clear faults first.

When to Choose Category B Over Category A

In practice, the deciding factor is selectivity strategy. If your switchboard has more than two protection levels — say, an incomer feeding sub-distribution boards which then feed motor control centers — you generally need a Category B device at the incomer to allow time grading. A Category A breaker will trip instantaneously on high faults, which can cause the upstream device to trip before the downstream one finishes, leading to unwanted blackouts.

For a 5000 A main bus tie in a refinery substation, we typically specify the ABB 1SDA071275R1 E6.2V 5000 Ekip Touch LSI. Its Icw of 100 kA / 1 s allows full time-current grading with downstream Category B feeders rated 1250 A and 630 A.

Type Tests Required by Clause 8

Clause 8 of IEC 60947-2 defines the verification regime that any breaker must pass before it can be marked as compliant. These tests are performed by the manufacturer or a third-party lab (KEMA, ASTA, CESI are the recognized authorities) and are not optional.

Test Sequence Overview

The standard groups tests into sequences. Sequence I covers general performance: temperature rise, dielectric, overload and mechanical/electrical durability. Sequence II covers Ics. Sequence III covers Icu. Sequence IV covers Icw (for Category B only). Sequence V covers combined sequence on a single sample for some product approvals.

One detail engineers often miss: the same physical breaker is not used for all sequences. Different samples are subjected to different sequences. So a manufacturer claiming Icu = 100 kA has tested a different unit than the one tested for Ics. This is standard practice but worth understanding when reviewing third-party test certificates.

The Often-Overlooked Mechanical Endurance Test

Clause 8.3.3.5 specifies mechanical endurance — the breaker must survive a defined number of operations without current. For frame sizes up to 630 A, that is typically 8000 cycles without maintenance plus 4000 with maintenance, totaling 12000 operations. The ABB 1SDA100425R1 XT5S 630 Ekip Dip LS/I exceeds this, with 12500 mechanical operations rated. For breakers used as switching devices in pumping stations where they cycle daily, mechanical endurance is more limiting than electrical endurance.

IEC 60947-2 vs UL 489 vs NEMA AB

For global procurement managers, the most consequential question is rarely "does this breaker meet IEC 60947-2?". It is "does this breaker meet IEC 60947-2 AND UL 489 for the US portion of our project?". The answer is usually no, and the reason is that the test methods differ in non-trivial ways.

The lower power factor in IEC tests means higher peak asymmetrical currents — making the IEC test arguably more severe for the same RMS rating. This is why many ABB MCCBs sold globally carry both IEC and UL certifications, but with different rated current values for each market. A breaker labeled 100 A under IEC may be derated to 80 A under UL, due to different temperature rise reference conditions (40°C ambient open air for IEC vs 25°C in enclosure for UL).

Selectivity and Cascading Under IEC 60947-2

Selectivity (also called discrimination in older European usage) is the ability of a downstream protective device to clear a fault before the upstream device trips. IEC 60947-2 supports two forms: current-based and time-based. Cascading (back-up protection) is different — it allows a downstream breaker with a lower Icu to be used because the upstream breaker assists in clearing the fault.

Current Selectivity

Current selectivity works when the prospective fault current at the downstream device is lower than the instantaneous trip threshold of the upstream device. This is typical when there is significant cable impedance between levels. For a 100 m run of 4×95 mm² Cu cable feeding a sub-distribution board, the line impedance reduces fault current enough that the upstream 630 A breaker's I trip (set at, say, 6×In = 3780 A) will not pick up.

Time Selectivity

Time selectivity uses the short-time delay (S function) of Category B breakers. The upstream breaker is set with a delay of 200–400 ms, allowing downstream Category A or B breakers with shorter delays to clear first. MCCB sizing for motor loads covers how the inrush current of large motors interacts with these settings.

Engineers often overlook the energy let-through (I²t) curves published by manufacturers. These are essential when verifying selectivity in the high-fault region where simple time-current curves overlap. ABB publishes I²t curves for the Tmax XT and Emax 2 families, and Schneider does the same for ComPact NSX. Without these, current-limiting selectivity claims are guesswork.

Accessories Covered Under IEC 60947-2

Auxiliary devices — undervoltage releases, shunt trips, auxiliary contacts, motor operators — are covered as part of the breaker assembly when supplied by the manufacturer and tested together. A field-installed third-party shunt trip on a certified breaker voids the IEC 60947-2 declaration unless re-tested.

The ABB 1SDA054892R1 UVR-C undervoltage release for Tmax T4-T5-T6 frames is a typical example. It is type-tested with the host breaker per Annex F requirements, and the response time (40 ms typical at 70% Un) is within the standard's mandate. For DIN-rail accessories on a different product line, the ABB 2CCS800900R0011 S800-AUX auxiliary contact block follows the same logic on the S800 series.

Practical Application: Specifying an MCCB for an Industrial Project

Let me walk through a real specification we wrote for a desalination plant feeder panel in Saudi Arabia. The project demanded IEC 60947-2 compliance, 50°C ambient inside the panel, 415 V three-phase supply with prospective short-circuit current of 65 kA RMS at the busbar.

The feeder was rated 1250 A continuous for a high-pressure pump VFD. The choice came down to ABB 1SDA072952R1 E2.2H 1250 Ekip Dip LSI 4-pole. Why this SKU? The H version provides Icu = Ics = 100 kA at 415 V — comfortably above the 65 kA prospective fault. Icw = 85 kA / 1 s gives full time selectivity with downstream 630 A and 250 A feeders. The 4-pole configuration was specified because the system grounding required neutral switching.

For smaller branch circuits in the same panel, we used ABB 1SDA067458R1 XT1H 160 TMD at 63 A and 100 A ratings, and 1SDA067460R1 XT1H 160 TMD 100A for the 100 A feeders. Both are Category A with Icu = 70 kA, sufficient because cable impedance limits downstream fault current to under 50 kA. ABB also offers comparable models for competitive comparison against Schneider and Siemens equivalents.

Common Mistakes in Specification

The mistakes we see most often: specifying Icu without Ics; ignoring temperature derating (a 250 A breaker at 40°C may carry only 220 A at 55°C ambient); confusing Class 2 trip accuracy with Class 1; and failing to verify the breaker's neutral pole is rated for full current (some 4-pole MCCBs have a 50% neutral). Each of these has triggered a real RFC (request for change) on projects we have audited. Some of these issues also drive nuisance tripping in operation, which is a separate but related problem.

How IEC 60947-2 Interacts with Other Standards

IEC 60947-2 does not exist in isolation. It ispart of a larger ecosystem of standards that engineers must navigate together. The breaker certified to 60947-2 still has to fit inside an assembly certified to IEC 61439 (low-voltage switchgear and controlgear assemblies), be coordinated with motor starters per IEC 60947-4-1, and may need to provide ground-fault protection per IEC 60947-2 Annex B for circuits requiring residual current detection.

IEC 61439 Assembly Requirements

IEC 61439-2 governs the panel itself. When a breaker is mounted in an assembly, the temperature rise verification of the assembly may impose derating beyond what the breaker's own datasheet specifies. A 1600 A E1.2 breaker rated for 40°C ambient open-air may need to be derated to 1440 A when installed in an enclosure where internal air reaches 55°C. The verification is done at the assembly level, not the device level. Many disputes between switchgear builders and end users come from misunderstanding this boundary.

Coordination with Motor Protection per IEC 60947-4-1

When an MCCB feeds a motor starter (contactor + overload relay), the coordination type — Type 1 or Type 2 — is defined by IEC 60947-4-1, not Part 2. Type 2 coordination requires that no damage occur to the contactor or overload relay other than light contact welding that can be cleared without replacement. The MCCB's energy let-through (I²t) is the limiting factor, and manufacturers publish coordination tables specifying which breaker matches which contactor. Mixing brands in a Type 2 chain invalidates the coordination claim.

Residual Current Protection

For circuits requiring earth-leakage detection, an MCCB may be combined with a residual current module, or a separate device from the residual current device range may be installed upstream. Annex B of IEC 60947-2 covers the integral solution; IEC 61008 and IEC 61009 cover standalone RCDs and RCBOs. The choice depends on whether you need adjustable trip levels (MCCB with RCM) or fixed sensitivity (standalone RCD).

Air Circuit Breakers vs Molded Case Under IEC 60947-2

Although this article focuses on MCCBs, IEC 60947-2 also covers air circuit breakers (ACBs). The standard does not formally distinguish the two — both are simply "circuit breakers" — but in practice, ACBs occupy the upper end of the rating spectrum (typically 800 A to 6300 A) and are almost always Category B. Browse air circuit breakers in stock to see the typical frame sizes.

For lower ratings, miniature circuit breakers (MCBs) are governed by IEC 60898 for residential and commercial use, or by IEC 60947-2 itself when used in industrial applications. The choice of standard determines the testing rigor: IEC 60898 has lower breaking capacity ceilings (typically 10 kA) and simpler trip curve definitions, while IEC 60947-2 allows MCBs up to 50 kA with more granular trip characteristics.

Documentation and Marking Requirements

Clause 6 of IEC 60947-2 specifies the markings that must appear on every compliant breaker. These include manufacturer name, type designation, rated current (In), rated operational voltage (Ue), Icu and Ics at each rated voltage, utilization category, IP rating of terminals, and the standard reference itself. Missing any of these allows customs authorities or inspection bodies to reject the device.

The accompanying documentation must include the type-test certificate (or a declaration of conformity referencing it), the time-current curves, the I²t curves, the temperature derating tables, and the wiring diagrams for any accessories. We recommend always requesting the manufacturer's "Technical Application" or "Technical Catalog" document for the specific series — ABB, Schneider, and Siemens all publish these freely. They contain coordination tables, selectivity charts, and accessory compatibility matrices that the brief datasheet omits. A primer on what a molded case circuit breaker is and how it functions may be a useful refresher before reading these technical documents.

Maintenance and Re-Verification Under IEC 60947-2

The standard does not mandate periodic re-testing of installed breakers. However, IEC 60364-6 (the inspection part of the wiring rules) does require periodic verification of installations, and many national codes require thermographic inspection annually. After a major short-circuit event, the standard implies but does not explicitly require that the breaker be inspected. In our experience, after any fault clearing close to Icu, the breaker should be replaced. After a fault closer to Ics, it can typically remain in service if visual inspection shows no damage.

For breakers protecting relay-controlled motor circuits or critical processes, we recommend a documented maintenance schedule including annual mechanical operation tests (open-close cycles without load), insulation resistance measurement at the breaker terminals, and trip unit calibration checks every 5 years.

Related Reading

• What Is a Molded Case Circuit Breaker (MCCB)? Function Explained
• MCCB Breaking Capacity: Icu, Ics and Icw Ratings Explained
• MCCB Sizing for Motor Loads: Formula, Calculator and Step-by-Step Guide
• ABB vs Schneider vs Siemens MCCB: Full Brand Comparison for Engineers

Conclusion

IEC 60947-2 is the engineering language of low-voltage circuit breaker selection. It defines what the ratings on the nameplate actually mean, how the manufacturer proves them, and how engineers must use them in coordination studies. The difference between a properly specified MCCB and a poorly specified one is not visible on the datasheet — it appears years later, during the first major fault or the first attempt at selective tripping. Specify Icu and Ics independently. Choose Category B where time selectivity matters. Verify Icw against the actual one-second fault current. Demand type-test certificates, not just markings. And remember that the breaker is only one part of an assembly governed by IEC 61439, coordinated with motor starters per IEC 60947-4-1, and operated under conditions defined by IEC 60364.

For the complete selection methodology — from frame size choice through commissioning — see the comprehensive Molded Case Circuit Breaker (MCCB) Guide: How It Works, Sizing, and Buying Tips. The standards exist to give every engineer a common reference. Use them, cite them by clause, and your specifications will speak the language that manufacturers, contractors, and inspectors all understand.