ABB SACE Emax 2 Air Circuit Breaker: Selection, Application and Maintenance Guide

What is the ABB SACE Emax 2 air circuit breaker? The ABB SACE Emax 2 is an IEC 60947-2–compliant low-voltage air circuit breaker available in four frame sizes from 800 A to 6300 A, with breaking capacities up to 150 kA at 690 V AC, designed for main and tie breaker applications in industrial and infrastructure power distribution. Specifying an incorrect frame rating, mismatching the Ekip trip unit to the load profile, or neglecting selectivity coordination can result in unwanted tripping, thermal damage to downstream equipment, or failed discrimination during fault events. This guide covers arc-quenching and trip unit operation, frame and rating selection methodology, an Emax 2 sizing calculator, fixed versus withdrawable construction tradeoffs, and selectivity coordination techniques.

Published: 2026-04-27 | Last updated: 2026-04-27 | By Stoklink Engineering Team

What Is the ABB SACE Emax 2 Air Circuit Breaker?

The ABB Emax 2 is the second-generation evolution of ABB's flagship air circuit breaker line, launched in 2014 to replace the original Emax (E1–E6) introduced in the late 1990s. In our experience commissioning LV switchboards across cement plants, data centers, and offshore platforms, what differentiates the Emax 2 from a generic ACB is not the breaking mechanism — most modern ACBs use comparable arc-chute geometries — but the integrated Ekip ecosystem and the embedded power analyzer.

The breaker is offered in four physical sizes, each scaled to a current and breaking capacity envelope:

• E1.2 — 630 A to 1600 A, breaking capacity Icu up to 66 kA at 415 V
• E2.2 — 800 A to 2500 A, Icu up to 100 kA
• E4.2 — 1600 A to 4000 A, Icu up to 150 kA
• E6.2 — 4000 A to 6300 A, Icu up to 200 kA

For the size, the E1.2 frame is unusually compact: 324 mm wide for a 1600 A 3-pole withdrawable unit. That matters when retrofitting older switchgear without expanding the busbar chamber. We have used this property to retrofit Emax E1 (legacy) into existing General Electric M-Pact panels using the official retrofit kit, with no busbar modification required.

Where the Emax 2 sits in the LV protection hierarchy

In a typical industrial single-line diagram, the Emax 2 occupies the top three protection layers: transformer secondary main incomer, bus-tie (coupler), and major outgoing feeders above 630 A. Below that level, engineers typically transition to molded-case circuit breakers (MCCBs) such as the ABB Tmax XT or Schneider Compact NSX, and below 125 A to miniature circuit breakers. The Emax 2 is rarely justified below 630 A on a pure cost basis — an MCCB does the job at one-third the price — but it is selected at lower currents when the application demands a high Icw (short-time withstand current) or extensive metering.

For complete technical specifications, performance curves, and Ekip trip unit configuration details, consult the official ABB SACE Emax 2 product documentation, which provides the manufacturer's authoritative reference for selecting and applying the ABB Emax 2 in low-voltage distribution systems.

How Does the Emax 2 Work? Arc Quenching, Mechanism and Trip Units

Understanding how the ABB Emax 2 operates matters because most field failures we have investigated stem from misapplication of the trip unit, not mechanical wear of the breaker itself.

Mechanical operation

The Emax 2 uses a stored-energy spring mechanism. A motor (or manual handle) charges the closing springs against an internal cam. When the close command is issued — by pushbutton, remote 24 V DC pulse, or communication — a closing solenoid releases the cam, the closing springs drive the moving contacts onto the fixed contacts in roughly 70 ms, and the opening springs simultaneously charge for the next trip. The opening time, on a fault, is typically 25–30 ms, with total clearing time around 45–60 ms depending on the arc extinction.

The arc-quenching method is conventional for ACBs in this class: the arc is drawn upward into a stack of steel plates (the arc chute) that splits the single arc into many shorter series arcs. Each sub-arc has a higher voltage drop near its electrodes, so the cumulative arc voltage exceeds the source voltage and forces the current to zero. Compared to molded-case breakers, the Emax 2 has a much larger arc-chute volume, which is why it can interrupt 100+ kA at 415 V without significant stress.

The Ekip trip unit family

This is where the Emax 2 differentiates itself. The Ekip platform is modular — Ekip Dip, Ekip Touch, Ekip Hi-Touch, Ekip G Touch, Ekip Hi-Touch Measuring — and the choice determines what protection functions, measurements, and communication options the breaker supports.

A common procurement mistake is to specify Ekip Hi-Touch on every breaker in a panel "for future-proofing." In practice, only the main incomer and bus-tie need that level of metering — outgoing feeders are best served by Ekip Dip LI or LSI to control cost. We see Ekip Dip LI versions, like the ABB 1SDA070701R1 E1.2B 630 Ekip Dip LI and the ABB 1SDA070741R1 E1.2B 800 Ekip Dip LI, used heavily on outgoing motor feeders where the upstream protection handles ground fault and the feeder itself only needs overload and instantaneous.

How Do Engineers Select the Right Emax 2 Frame and Rating?

Selecting an ABB Emax 2 is more than picking a current. It is a five-axis decision: rated uninterrupted current Iu, rated service breaking capacity Ics, short-time withstand Icw, system voltage Ue, and trip-unit configuration. Get any one wrong, and the breaker either trips nuisance-style or fails catastrophically under fault.

Step 1: Determine the load current

Start with the calculated full-load current of the protected circuit. For a transformer secondary, this is straightforward — the transformer nameplate gives the rated secondary current. For a bus, sum the diversified load currents. Apply a sizing margin: most designers use Iu ≥ 1.25 × Iload for continuous duty, per NEC 215.2(A)(1) and IEC 60364-4-43 §433.1.

Worked example: a 1600 kVA, 415 V transformer gives I_FL = 1600 × 1000 / (1.732 × 415) ≈ 2226 A. Applying a 25% margin yields 2783 A, so an E4.2 frame at 3200 A is the natural fit. The next frame down — E2.2 at 2500 A — is too tight for steady-state operation plus a 10% transformer overload tolerance.

Step 2: Calculate the prospective short-circuit current

This determines Icu (ultimate breaking capacity) and Icw (short-time withstand). The prospective fault current at the bus is:

For the same 1600 kVA transformer at u_k = 6%, I_sc = 1600 × 100 / (1.732 × 415 × 6) ≈ 37 kA. An E2.2B at 42 kA Icu is sufficient. If the upstream MV network contributes significantly — say, infinite-bus assumption gives 50 kA — you would specify the E2.2N at 65 kA or E2.2H at 85 kA.

Step 3: Select the trip unit

Match the trip unit to the protection scheme. For selectivity coordination with downstream MCCBs, you need at least an LSI trip unit so the short-time delay can be set to ride through downstream instantaneous trips. The ABB 1SDA070782R1 E1.2B 1000 Ekip Dip LSI is the typical choice for a 1000 A feeder requiring time-graded selectivity.

Emax 2 Sizing Calculator

Fixed vs Withdrawable: Which Construction Should You Specify?

This question recurs in nearly every ABB Emax 2 project review. The honest answer is: it depends on maintenance philosophy and downtime cost.

Fixed versions bolt directly to the busbars. They cost roughly 30% less than withdrawable, occupy less depth, and are mechanically simpler. The downside is that any maintenance — contact inspection, mechanism greasing, trip unit replacement — requires de-energizing the bus. In a 24/7 facility this is unacceptable.

Withdrawable versions sit in a cassette. The breaker can be racked out to the test position (control circuits live, power circuits isolated) or fully withdrawn for replacement, all while the busbar remains energized. This is mandatory in data centers, hospitals, and continuous process plants.

In practice, we specify fixed versions like the ABB 1SDA070821R1 E1.2B 1250 and the ABB 1SDA070861R1 E1.2B 1600 on outgoing feeders to large but non-critical loads (HVAC, lighting subpanels), and reserve withdrawable for incomers and bus-ties. This blended approach typically saves 15–20% of switchboard cost without sacrificing reliability where it matters.

How Do You Coordinate Selectivity With an Emax 2?

Selectivity (also called discrimination) is the property of a protection system where only the breaker closest to the fault opens, leaving the rest of the network energized. With ACBs such as the ABB Emax 2 as the upstream device and MCCBs or fuses downstream, achieving total selectivity up to the bus fault current is non-trivial.

Time-current selectivity

The Emax 2's short-time delay (S function) is what makes selectivity possible. A typical setting on a main incomer is I2 = 6 × In with t2 = 0.4 s. This lets a downstream MCCB clear its instantaneous trip in roughly 30 ms while the upstream Emax holds the fault for the remaining time. The fault clears, the downstream device opens, the upstream device times out without operating.

The constraint is Icw. If the upstream Emax 2 must hold 50 kA for 0.4 s, you need an E2.2B with Icw = 42 kA/1 s minimum, or an E2.2N at 65 kA/1 s. Engineers often overlook this and specify a breaker whose Icw is below the Icw required for the selected delay — the breaker will trip on its own thermal limit before the downstream device has cleared, causing nuisance bus shutdowns during downstream faults.

Energy-based (zone selective interlocking)

The Ekip ZSI feature provides zone selective interlocking via a hardwired or bus signal. When a downstream breaker detects a fault and signals upstream, the upstream Emax 2 holds its short-time delay at its programmed value. If no downstream signal is received, the upstream device reduces its delay to typically 80 ms, clearing the fault much faster. This is critical for arc-flash mitigation per NFPA 70E and IEEE 1584.

Comparing the Emax 2 to Schneider, Siemens and Eaton

Procurement teams ask this constantly. The honest summary: all four major platforms — ABB Emax 2, Schneider MasterPact MTZ, Siemens 3WL, Eaton Power Defense — meet IEC 60947-2 and the ratings overlap heavily. The differences are in trip-unit ergonomics, communication protocols, retrofit footprint, and regional spare-part availability.

In our experience, the Emax 2 wins on physical compactness and Bluetooth-based commissioning (the Ekip Bluetooth module lets engineers set parameters via mobile app without opening the panel — a real time saver during commissioning). MasterPact MTZ wins on the Micrologic X user interface, which most field engineers find more intuitive on first encounter. Siemens 3WL has the strongest pedigree in heavy industry and the deepest selectivity tables. Eaton is competitive on price but has narrower availability outside North America.

Where Is the Emax 2 Used? Real-World Applications

The ABB Emax 2 shows up across the industrial spectrum, but each sector imposes its own selection logic.

Data centers

In Tier III and Tier IV data centers, the Emax 2 typically serves as the main incomer on each utility feed and as the bus-tie in the main distribution board (MDB). The driver is uptime: every minute of unplanned downtime in a colocation facility costs the operator anywhere from $5,000 to $50,000 depending on SLA. That is why we see withdrawable E2.2 and E4.2 frames with Ekip Hi-Touch trip units on every incomer — the metering and Modbus communication feed directly into the DCIM system, and the withdrawable cassette allows hot maintenance.

For a typical 2 MW IT load at 400 V, the main incomer current is roughly 2900 A, which lands on an E4.2 at 3200 A. We commonly use the ABB 1SDA071021R1 E2.2B 2000 Ekip Dip LI on UPS output feeders and the ABB 1SDA070981R1 E2.2B 1600 Ekip Dip LI on critical mechanical loads (chillers, CRAH banks).

Oil and gas, offshore platforms

Offshore LV switchboards face salt-laden atmospheres, vibration, and limited maintenance windows. Specifications typically demand IEC 60068 vibration tests, conformal coating on electronics, and ATEX-zone segregation. The Emax 2 holds DNV and ABS marine-type approvals, which simplifies vendor approval. The trade-off is that we usually upsize Icw by one step on offshore projects, because rotating-machine fault contributions on platforms are heavy and the typical fault duration before generator decay is longer than onshore.

Cement, steel and heavy process

In a cement plant we commissioned in North Africa, the kiln main drive (a 6 MV motor with VFD) sits behind an Emax 2 E4.2 at 4000 A as the LV switchgear incomer. The challenge there is harmonic content — the VFD pushes 4–7% THD into the upstream bus. Ekip Hi-Touch Measuring captures this and feeds it to the plant SCADA, which has helped operators justify a harmonic filter retrofit by quantifying the actual distortion rather than relying on design assumptions.

Renewable energy plants

In solar farms, the Emax 2 typically sits on the LV side of the inverter step-up transformer. The unusual constraint is bidirectional power flow: the breaker may export power to the grid most of the day and import small auxiliary loads at night. Standard L-protection works, but G (ground fault) requires care because solar inverters can produce DC ground-fault components that fool conventional residual sensors. The Ekip trip units handle this with a dedicated DC-immune residual sensor option.

Healthcare facilities

Hospitals fall under IEC 60364-7-710, which mandates IT (isolated terra) systems for Group 2 medical locations like operating theatres. The main LV switchboard upstream usually uses the Emax 2 with full LSIG protection, but the IT subsystem itself uses insulation monitoring devices and avoids upstream G protection that would defeat the purpose of the IT system. A common mistake is to enable G protection on the Emax 2 feeding the IT transformer — the first phase-to-ground fault then trips the upstream breaker instead of merely raising an alarm. The trip unit's G function should be disabled for IT-system feeders and replaced with insulation monitoring per IEC 61557-8.

What Are the Most Common Field Problems With the Emax 2?

No platform is immune to operational issues, and the ABB Emax 2 is no exception. Here are the recurring ones we see and how to diagnose them.

Nuisance tripping under normal load

The most frequent root cause is incorrect L-function setting. The Emax 2's long-time pickup I1 has a tolerance of ±10% per IEC 60947-2 §8.3.4.1. If the setting is at 0.95 × In and the actual continuous load is 0.92 × In with normal harmonics raising true RMS to 0.97, the breaker trips after roughly 15 minutes. The fix is to recalculate the actual operating current including harmonic content (the Ekip Hi-Touch displays this directly under the "I rms" parameter) and set I1 ≥ 1.10 × I_actual.

The second most common cause is current-transformer (CT) saturation in the rating plug for breakers operating well below their nameplate. An E4.2 at 3200 A used to protect a 1500 A feeder will measure with reduced accuracy. The remedy is the appropriate rating plug — ABB ships rating plugs in increments (e.g., R3200, R2500, R1600) so the CT is matched.

Breaker won't close

If the springs are charged but the closing command produces no result, the most common culprits in order of probability are: (1) the breaker is in the OPEN-LOCKED state due to an undervoltage release with no control voltage, (2) the racking interlock is not in either CONNECTED or TEST position, (3) the spring-charged microswitch is mis-aligned after maintenance, (4) the closing solenoid (Y1) coil has failed. The Ekip trip unit's event log records the reason — always read it before disassembling.

Communication dropouts

For Modbus RTU, the typical issue is RS-485 termination. The Ekip Com module needs a 120 Ω termination at each end of the daisy chain. We have walked into panels where five Emax 2s are paralleled on Modbus and only the first and last had termination — the middle ones polled intermittently for months until someone noticed. For IEC 61850, the more common issue is GOOSE message timing — keep the publishing interval ≥4 ms and ensure VLAN segregation if the network carries non-protection traffic.

How Do You Maintain the Emax 2 Over Its Service Life?

The ABB Emax 2 is rated for a mechanical endurance of 12,500 to 25,000 operations depending on frame, and an electrical endurance of 6,000 to 10,000 operations at rated current. In a typical industrial application — incomer that opens perhaps 50 times per year for maintenance and tests — the breaker will outlive the switchgear it sits in. But that is only true if maintenance is performed on schedule.

Recommended maintenance intervals

Contact wear assessment

The Emax 2 has a wear indicator on each pole — a colored band on the moving contact carrier visible through the front window. When the band reaches the limit mark, contact replacement is due. In practice, this happens after roughly 70% of the rated electrical endurance has been consumed. Engineers often overlook the wear indicator because it requires racking the breaker out to inspect; we recommend including this step in the 3-year preventive maintenance procedure rather than treating it as a separate task.

Lubrication: do not over-grease

A frequent field error is applying generic grease (often lithium-based EP2) to the closing mechanism. The wrong grease attracts dust, hardens at low temperatures, and can cause closing failures in cold storage warehouses or unheated outdoor enclosures. ABB specifies a specific polyurea grease compatible with the steel surfaces and rubber seals; substituting it voids the warranty and, more importantly, changes the friction characteristics of the mechanism enough to affect closing time.

Procurement Considerations: Lead Time, Spare Parts and Total Cost

For procurement managers, the Emax 2 is not a commodity. Stock availability, retrofit-kit compatibility, and trip-unit lead times all influence project schedules.

Standard vs configured lead times

Common configurations — E1.2B and E2.2B with Ekip Dip LI in 3P fixed format — typically ship from European stock in 2–4 weeks. Custom configurations (Ekip Hi-Touch with IEC 61850, Withdrawable HR terminals, neutral pole at 200%) extend to 8–14 weeks. We recommend that procurement teams build a stock list of the four most-used SKUs in their facilities — typically the 630 A, 1000 A, 1600 A, and 2000 A frames in fixed Ekip Dip LI configuration — and keep at least one of each on the shelf.

Spare parts strategy

The critical spares for an Emax 2 fleet are: (1) Ekip trip units in matched ratings, (2) closing/opening solenoids (Y1, YO, YU), (3) auxiliary contact blocks, (4) rating plugs sized to the application, (5) main contacts (typically delivered as a kit per pole). The total spare cost for an "incomer-grade" kit is roughly 15% of a new breaker — modest insurance against a 4–14 week lead time.

Total cost of ownership

Sticker price is misleading. A useful rule from our project history: over a 25-year service life, the breaker purchase represents roughly 30% of total cost; commissioning and testing 10%; energy losses through the breaker's contacts (a function of contact resistance and load profile) 35%; and maintenance plus eventual refurbishment 25%. Specifying a slightly oversized frame — say E2.2 at 2000 A instead of E1.2 at 1600 A for a 1400 A continuous load — reduces I²R losses across the contacts by roughly 35% and pays back the upcharge within 6–8 years through energy savings alone.

Integration With Other LV Devices

The Emax 2 rarely operates in isolation. It coordinates upstream with MV protection (typically ABB Relion REF615 or REF620 relays on the transformer primary) and downstream with MCCBs, motor starters, and final-circuit protection.

For motor feeders, the typical chain is Emax 2 main → MCCB feeder → contactor → overload relay. The contactor-overload combination can be a Type 2 coordinated pair from the Stoklink contactor collection, while the MCCB selection draws from the moulded case circuit breaker collection. For final circuits below 125 A, MCBs from the miniature circuit breaker collection handle individual loads.

Ground-fault protection is split between the Emax 2's G function (for the bus and major feeders) and dedicated residual current devices on the small final circuits where personnel protection is the goal. Auxiliary control logic — interlocks, automatic transfer, alarm aggregation — is typically built around a panel of control relays and Modbus interface modules wired to the Ekip trip unit.

For the broader portfolio of frame ratings and ordering options, the air circuit breakers collection at Stoklink lists the current Emax 2 SKUs with availability and lead-time information.

Standards Compliance: What the Emax 2 Is Tested To

The Emax 2 is type-tested to IEC 60947-2 (low-voltage circuit breakers), with the relevant clauses being §7 (rated values), §8 (type test sequence), and §9 (routine tests). It also holds compliance with:

UL 1066 — Low-Voltage AC and DC Power Circuit Breakers Used in Enclosures, for the North American market. The UL-listed versions have slightly different rating designations and a separate part-number range (e.g., E1.2N-A is the UL variant of the IEC E1.2N).

ANSI C37.50 — North American test procedures for low-voltage power circuit breakers, applicable to the UL-listed variants.

NEMA AB-1 — Molded-case and low-voltage power circuit breaker general requirements; the Emax 2's integrally-fused versions reference NEMA AB-1 §5.

IEEE C37.13 — Standard for low-voltage AC power circuit breakers used in enclosures; defines the LSIG protection nomenclature used in the Ekip trip units.

IEC 61000-6-2 / 61000-6-4 — EMC immunity and emission standards. The Ekip trip units are tested for industrial-environment immunity, which matters in installations near MV switchgear or VFD-heavy plants.

Marine and offshore approvals include DNV-GL, ABS, Lloyd's Register, RINA, and BV — relevant for shipboard, FPSO, and offshore wind installations. Procurement teams specifying for marine projects should request the certificate package early, because some certificates are tied to specific configurations and not the generic frame.

Related Reading

• How to Size ABB Emax 2: Step-by-Step Calculator for LV Distribution Panels
• ABB Emax 2 Selectivity Coordination: Calculation Method and Selectivity Tables
• ABB Emax 2 vs Schneider MasterPact MTZ: Technical Specs, Features and Price Compared
• ABB Emax 2 Maintenance Procedure: Inspection Schedule, Lubrication and Test Protocol
• ABB Emax 2 Ekip Trip Units Explained: Types, Functions and Selection

Conclusion

The ABB SACE Emax 2 is a mature, well-supported low-voltage air circuit breaker platform that delivers strong performance across industrial, commercial, and infrastructure applications. Its strengths — compact footprint, modular Ekip trip-unit ecosystem, native communications, and broad standards compliance — make it the default specification on many global engineering projects. Its weaknesses are cost relative to MCCBs at lower currents and the learning curve required to use the Ekip platform fully.

Selection comes down to disciplined sizing: calculate full-load and short-circuit currents accurately, choose Iu with a 25% margin, pick Icw to support your selectivity scheme, and match the trip unit to actual functional requirements rather than over-specifying. Maintenance is straightforward but unforgiving of neglect — annual inspections, three-year secondary injection, five-year lubrication. Procurement is straightforward when standardizing on common SKUs and keeping critical spares on the shelf.

For the full selection methodology that places the Emax 2 within the broader context of low-voltage protection design, see our Air Circuit Breaker engineering guide. For ordering specific frames and trip-unit configurations discussed throughout this article, the air circuit breakers collection at Stoklink lists current availability, technical datasheets, and SKUs across the Emax 2 range.