Air Circuit Breaker IEC 60947-2 Standard Explained for Engineers

What is IEC 60947-2? IEC 60947-2 is the international standard governing low-voltage circuit breakers, including air circuit breakers (ACBs) rated up to 1000 V AC, defining performance requirements for breaking capacity, utilization categories, and type-test verification. Specifying an ACB without verifying its Icu, Ics, and Icw ratings against this standard risks inadequate fault interruption, failed selectivity coordination, or regulatory non-compliance on protected installations. This guide covers utilization categories A and B, the distinction between Icu, Ics, and Icw short-circuit ratings, nameplate interpretation per IEC 60947-2, selectivity frameworks, and mandatory temperature-rise, dielectric, and mechanical endurance test requirements.

What is IEC 60947-2 and why does it matter for ACB selection?

IEC 60947-2 is Part 2 of the IEC 60947 series, "Low-voltage switchgear and controlgear — Circuit breakers." Part 1 (IEC 60947-1) defines the general rules common to all switchgear; Part 2 specializes those rules for circuit breakers. If you are buying an ACB for a 690 V switchboard in a cement plant, the type test certificate you ask the manufacturer for is almost always against IEC 60947-2 — not against IEC 60898, which applies to household MCBs, and not against UL 489, which is the North American equivalent for branch-circuit breakers.

In our experience, procurement teams treat the standard as a checkbox. Engineers should treat it as a contract. Every parameter on the breaker nameplate — Ue, Ui, Uimp, Icu, Ics, Icw, Ir, Im, Ig — has a defined meaning under IEC 60947-2, and a defined test sequence behind it. When a specification says "ACB compliant with IEC 60947-2," what it really means is that the manufacturer has performed the O-CO-CO duty cycle (open, close-open, close-open) at the declared short-circuit current and the breaker passed the post-test dielectric verification.

How IEC 60947-2 differs from IEC 60898 and UL 489

A common mistake on tender documents is mixing standards. IEC 60898 is for circuit breakers intended for use by uninstructed persons in homes — it caps at 125 A and 25 kA. IEC 60947-2 has no such restriction; ACBs at 6300 A and 150 kA Icu are squarely in scope. UL 489 is the listing standard for North American molded-case breakers and uses different test methods (different power factors at fault, different temperature reference). A breaker dual-listed to both IEC 60947-2 and UL 489 will carry two separate ratings on the nameplate, often with different kA values, because the test conditions differ.

Understanding utilization categories A and B

This is where most engineers stop reading the standard, and where most selectivity problems begin. For an ACB, IEC 60947-2 Clause 4.4 defines two utilization categories:

Category A: Circuit breakers without a specifically declared short-time withstand current (Icw). They are designed to clear a fault as fast as possible. Most molded-case breakers fall here.

Category B: Circuit breakers with a declared Icw, capable of carrying a short-circuit current for a defined time (typically 1 s, sometimes 3 s) without tripping instantaneously. This is what allows time-graded selectivity. Air circuit breakers are almost always Category B.

Why does this matter? Picture a typical industrial main-tie-main lineup at a 2.5 MVA substation. The incomer is an ABB Emax 2 E2.2B 2000 A, the feeders are 630 A and 800 A E1.2 frames, and downstream are 250 A MCCBs. If a fault occurs on a feeder, you want the feeder breaker to clear it — not the incomer. To achieve that, the incomer must be able to ride through the fault current for the duration the feeder breaker takes to clear, plus a margin. Only a Category B breaker with a declared Icw can do this. The ABB 1SDA071021R1 E2.2B 2000 A declares Icw = 42 kA for 1 s, which gives the upstream protection engineer the headroom to set a 200–300 ms intentional delay.

When Category A is acceptable

Category A is fine for the last protective device in a radial system — typically MCCBs feeding final motor circuits or lighting panels. There is nothing downstream that needs to coordinate, so instantaneous tripping is desirable. Engineers often overlook this and over-specify Category B everywhere, paying a 30% price premium for performance they never use.

Icu vs Ics vs Icw: the three short-circuit ratings explained

If there is one section of IEC 60947-2 worth memorizing for ACB selection, it's Clause 8.3.5 on short-circuit performance. The standard defines three distinct short-circuit currents, and confusing them is the single most common source of under-rated switchgear in the field.

Icu — rated ultimate short-circuit breaking capacity: the maximum prospective fault current the breaker can interrupt once. The test sequence is O – t – CO. After the test, the breaker is not required to be reusable for normal service; it must only be safe (no fire, no shock hazard) and capable of carrying its rated current.

Ics — rated service short-circuit breaking capacity: the fault current the breaker can interrupt and remain in service. Test sequence: O – t – CO – t – CO. After the test, the breaker must still meet its dielectric and temperature-rise specs. Ics is declared as a percentage of Icu: 25%, 50%, 75%, or 100%.

Icw — rated short-time withstand current: covered above.

In practice, what we typically see in the field: a tender specifies "Icu = 65 kA" and stops there. The supplier delivers a breaker with Icu = 65 kA and Ics = 50% × Icu = 32.5 kA. The plant suffers a 50 kA bolted fault three years later. The breaker clears it — Icu was sufficient — but the post-fault inspection finds carbonized arc chutes and welded contacts. The breaker is junked. The engineering specification should have demanded Ics = 100% × Icu for any breaker upstream of critical loads.

How to read an ACB nameplate per IEC 60947-2

Pull up an ABB Emax 2 datasheet — for example the ABB 1SDA070861R1 E1.2B 1600 A. The nameplate is dense. Here is how to decode it field by field, with the relevant IEC 60947-2 clause:

• Ue (rated operational voltage): 690 V AC. The voltage at which the breaking capacity is verified. Clause 4.3.1.1.
• Ui (rated insulation voltage): 1000 V. The reference for dielectric tests. Clause 4.3.1.2.
• Uimp (rated impulse withstand voltage): 12 kV. Lightning impulse withstand, 1.2/50 µs waveform. Clause 4.3.1.3.
• In (rated current): 1600 A at 40 °C ambient. Derate per Clause 4.3.2.4 above this.
• Icu / Ics / Icw: e.g., 42/42/42 kA at 415 V. All three equal — this is a B-class breaker with full ride-through.
• Utilization category: B, per Clause 4.4.
• IP code: typically IP20 for the breaker itself; the cubicle provides higher ingress.

For a deeper breakdown of every nameplate parameter, see ACB Technical Specifications: Ratings, Parameters and Definitions.

Selectivity and the IEC 60947-2 framework

Selectivity (or discrimination) is the property of a protection scheme where only the breaker closest to the fault opens. IEC 60947-2 Annex A defines two types:

Total selectivity: achieved up to the lower of the two breakers' Icu. The downstream breaker always clears first regardless of fault magnitude.

Partial selectivity: achieved only up to a defined limit current Is. Above Is, both breakers may trip simultaneously.

Manufacturers publish selectivity tables — ABB calls them "discrimination tables," Schneider uses "coordination tables." These are valid only when both breakers are from the same manufacturer's published combinations. Mix vendors and you are on your own; you must verify with time-current curves and possibly a real fault test.

Some engineers argue mixing vendors is fine if the curves look right on paper. In my experience, curves don't capture dynamic effects: the let-through I²t of an upstream current-limiting breaker can dip below the trip threshold of a downstream electronic trip unit during the first half-cycle, causing nuisance tripping that no static curve study predicts. For more on this failure mode, see Air Circuit Breaker Nuisance Tripping: Causes, Diagnosis and Fixes.

Worked example: 1600 A incomer with 630 A feeders

Consider a typical scenario: an ABB 1SDA070861R1 E1.2B 1600 A incomer with three ABB 1SDA070701R1 E1.2B 630 A feeders. Both are Category B with Icw = 42 kA / 1 s. Set the feeder Ekip Dip LI trip units to instantaneous at 6 × In = 3780 A. Set the incomer with a short-time delay (S function — note this requires the LSI version, e.g., the ABB 1SDA070702R1 LSI variant) at 0.2 s and pickup at 8 × In = 12,800 A. A fault on a feeder up to ~12 kA will be cleared by the feeder alone; the incomer rides through. This is total selectivity in practice.

Temperature rise, dielectric, and mechanical endurance tests

IEC 60947-2 doesn't only specify short-circuit performance. The full type-test sequence in Clause 8.3 includes:

Temperature rise (Clause 8.3.3.3): The breaker carries rated current until thermal equilibrium. Terminal temperature rise must not exceed 65 K (silver-plated) or 55 K (bare copper). This is why proper torque on cable terminations matters — a loose joint adds resistance, generates heat, and pushes the breaker past its tested limit.

Dielectric (Clause 8.3.3.4): Power-frequency withstand at 2 × Ui + 1000 V for 1 minute, plus impulse at Uimp.

Mechanical endurance (Clause 8.3.4): Number of no-load operations. For ACBs, typically 10,000 operations for the breaker frame and 25,000 with maintenance. The ABB E1.2B 800 A declares 12,500 mechanical operations.

Electrical endurance (Clause 8.3.4): Operations under load. Typically 10% of mechanical endurance.

IEC 60947-2 vs IEEE/ANSI C37 and NEMA AB

For projects spanning continents — say, an EPC building a refinery in the Middle East with North American owner standards — engineers must reconcile IEC 60947-2 with the IEEE/ANSI C37 family and NEMA AB standards. The differences are not cosmetic.

NEMA AB-1 and AB-3 are the application guides; the listing standard is UL 489. For ACBs in particular, IEEE C37.13 is the closer cousin to IEC 60947-2 Category B — both contemplate a drawout breaker with declared short-time withstand. A breaker compliant with IEC 60947-2 is generally not directly substitutable for a UL 489 breaker in a US-code project without re-listing, even if the ratings look equivalent on paper.

Practical specification language for procurement

Procurement managers ask: what should the spec sheet actually say? Here is field-tested language for an industrial ACB tender:

"Air circuit breakers shall comply with IEC 60947-2:2016, utilization category B, with manufacturer type-test certificates from an accredited laboratory (KEMA, ASTA, CESI, or equivalent). Icu and Ics shall both be 100% rated at 65 kA minimum at 415 V AC. Icw shall be not less than 50 kA for 1 s. Trip units shall be electronic with LSIG functions and ammeter, complying with IEC 60947-2 Annex F (electromagnetic compatibility) and Annex H (digital communication where specified). All breakers shall be drawout, three-position (connected/test/isolated) with key interlocks per IEC 60947-2 Clause 7.1.10."

This wording closes the typical loopholes: it forbids 50% Ics, demands Icw, requires accredited test certificates, and pins down the trip unit functions. For a complete sizing methodology including cable coordination, see How to Size an Air Circuit Breaker.

Frame size selection by application

Quick reference for matching frame to application, all IEC 60947-2 Category B:

• Small commercial substation (≤500 kVA): E1.2B 630 A incomer.
• Medium industrial (800–1000 kVA): E1.2B 800 A or E1.2B 1000 A.
• Large industrial (1250–1600 kVA): E1.2B 1250 A or E1.2B 1600 A.
• Heavy industrial / data center (≥2000 kVA): E2.2B 1600 A or E2.2B 2000 A with HR (horizontal rear) terminals for busbar connection.

For data center applications specifically, where the prospective fault current at the main switchboard often exceeds 50 kA and selectivity with downstream PDU breakers is critical, see Air Circuit Breakers in Data Centers: Selection and Design Best Practices. For brand-level trade-offs between Emax 2, Masterpact MTZ, and Siemens 3WL, consult ABB vs Schneider vs Siemens ACB: Brand Comparison for Engineers.

Common compliance failures during FAT and SAT

Factory Acceptance Tests (FAT) and Site Acceptance Tests (SAT) are where IEC 60947-2 stops being theoretical. Here are the failure modes we keep seeing:

Wrong test certificate. The supplier produces a certificate for a similar frame size, not the exact catalog number ordered. IEC 60947-2 Clause 8.3 type tests are valid only for the tested specimen. Always demand the certificate matches the SKU on the delivery note.

Field-installed accessories voiding type test. A common scenario: the breaker arrives without a shunt trip, an electrician installs an aftermarket coil. The breaker's type test, particularly the dielectric verification, is no longer valid. Use only the manufacturer's catalog accessories. The Ekip Dip protection module on ABB Emax 2 is integral; never substitute.

Incorrect torque on terminations. The temperature-rise test (Clause 8.3.3.3) was performed at the manufacturer's specified torque. A 1600 A horizontal terminal typically requires 70 N·m on M12 bolts. We have measured installations at 35 N·m where the assembler "didn't have a calibrated wrench." The result: 25 K extra rise, contact erosion, eventual failure.

Settings drift from the relay study. The protection coordination study specifies Ir = 0.9 × In, tr = 12 s, Im = 8 × In. The commissioning team accepts the breaker at default factory settings. First fault, the wrong breaker trips. Always verify trip unit settings match the latest issue of the protection study, signed and dated.

The standard's evolution: 2016 edition and what's coming

IEC 60947-2 has been amended several times. The current widely cited edition is 2016, with Amendment 1 in 2019 and Amendment 2 in 2023. The 2023 amendment formalizes requirements for digital communication interfaces (Modbus, Profibus, IEC 61850 mappings) under Annex U, and tightens requirements for cybersecurity in trip units that expose Ethernet ports.

The next edition, expected to align more tightly with IEC 61439 (the assembly standard), will introduce a more granular concept of "system rated short-time withstand" — recognizing that an ACB does not operate in isolation but as part of a switchgear assembly with busbars, droppers, and CTs that all share the fault. This is overdue. We have all seen incidents where the breaker was perfectly rated at 65 kA but the busbar bracing was rated at 50 kA, and the assembly let go before the breaker tripped.

Procurement should track these revisions. A breaker certified to IEC 60947-2:2006 may technically still be sold, but in a switchgear assembled with such a breaker will struggle to meet IEC 61439 type test requirements and may not be accepted by insurers like FM Global or risk consultants on greenfield sites.

Quick-reference clause map

For engineers who want a shortcut to the most-referenced clauses:

• Clause 4.3: Rated values — Ue, Ui, Uimp, In, Icu, Ics, Icw.
• Clause 4.4: Utilization categories A and B.
• Clause 7.2: Constructional requirements.
• Clause 8.3.3: Verification of dielectric properties and temperature rise.
• Clause 8.3.4: Mechanical and electrical endurance.
• Clause 8.3.5: Short-circuit performance (Icu, Ics, Icw test sequences).
• Annex A: Discrimination/selectivity between circuit breakers.
• Annex F: Additional requirements for circuit breakers with electronic over-current protection.
• Annex H: Test sequences for derating, communication, etc.
• Annex M: Modular residual-current devices integrated with circuit breakers.

Bookmark this. Most engineering disputes on a project can be resolved by pointing to one of these clauses with the correct edition reference.

Where IEC 60947-2 intersects other low-voltage standards

IEC 60947-2 doesn't live alone. A practicing engineer needs to know how it dovetails with adjacent standards. The breaker sits inside an assembly governed by IEC 61439-1/2, fed by cables sized per IEC 60364-5-52, protecting a system designed per IEC 60364-4-43 (overcurrent) and IEC 60364-4-41 (shock protection). The full air circuit breaker range at Stoklink, the miniature circuit breaker range for downstream final circuits, the residual current device collection for earth-fault protection, and the relay collection for control circuits all interact within the same IEC framework.

A specific intersection worth noting: when an ACB integrates a residual-current function (Ekip Dip with Rc module on Emax 2), it must comply with both IEC 60947-2 Annex M and IEC 60947-2 Annex B. The two annexes have overlapping but not identical test requirements. Always confirm the manufacturer claims compliance with both, not one.

Conclusion

IEC 60947-2 is not a bureaucratic hurdle — it is the engineering language that lets a procurement engineer in Singapore, a panel builder in Italy, and a commissioning engineer in Brazil agree on what a circuit breaker actually does. Master the distinction between Icu, Ics, and Icw. Insist on Category B with declared Icw for any breaker that participates in selectivity. Read the nameplate and tie every parameter back to its clause. Demand type-test certificates that match the SKU. Specify torque values and trip unit settings in commissioning documentation, because compliance is not preserved by accident.

The standard rewards rigor. Plants where engineers treat IEC 60947-2 as a working document run for decades on the same switchgear; plants where it is treated as a marketing claim suffer the avoidable failures that fill incident reports. For the full selection methodology — from load analysis through sizing, brand selection, and commissioning — see the parent Air Circuit Breaker Engineering Guide, which weaves IEC 60947-2 compliance into every step of the workflow.