How Does the ABB Emax 2 Circuit Breaker Work? Complete Guide

What is the ABB Emax 2 circuit breaker? The ABB Emax 2 is an air circuit breaker rated 400–6300 A at up to 1000 V AC under IEC 60947-2, delivering breaking capacities up to 200 kA Icu and integrating a digital Ekip trip unit for protection, measurement, and communication within low-voltage main and tie-breaker applications. Undersizing the frame rating, misconfiguring Ekip protection thresholds, or neglecting zone selective interlocking coordination can result in contact welding, loss of selectivity, or cascading busbar faults. This guide covers the closing and opening mechanism, Ekip trip unit sensing and decision logic, arc chute interruption physics, selectivity and zone selective interlocking schemes, and power management via communication protocols.

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

What Is the ABB Emax 2 and Where Does It Sit in a Distribution System?

The ABB Emax 2 is the second generation of ABB's SACE Emax platform, launched in 2014 and now the workhorse ACB across European, Middle Eastern and Asian LV switchboards. It replaces the original Emax (E1–E6) and slots between molded-case circuit breakers (MCCBs like Tmax XT) and medium-voltage gear. In a typical industrial main distribution board (MDB), you will find an Emax 2 acting as the incomer from a transformer secondary, plus several Emax 2 frames as outgoing feeders to subdistribution panels and large motor control centers.

The family covers four frame sizes: E1.2 (up to 1600 A), E2.2 (up to 2500 A), E4.2 (up to 4000 A) and E6.2 (up to 6300 A). Breaking capacities range from 42 kA on a standard E1.2B such as the ABB 1SDA070701R1 E1.2B 630 up to 200 kA on the high-performance V variants. For a complete breakdown of ratings and dimensions, see our reference on ABB Emax 2 full technical specifications.

For complete technical specifications and protection settings of the ABB Emax 2 air circuit breaker family, refer to the manufacturer's official ABB SACE Emax 2 product documentation, which details compliance with IEC 60947-2 and the full range of Ekip trip unit configurations.

How Does the Operating Mechanism Actually Close and Open the Contacts?

In our experience, this is the part most engineers gloss over until something fails on commissioning. The ABB Emax 2 uses a stored-energy spring mechanism — the same architecture ABB has refined since the 1990s — but with redesigned linkages that reduce closing time to under 80 ms.

Spring Charging

The closing springs can be charged manually using the front handle (typically 4–6 strokes) or automatically by a geared motor (M motor, 24–250 V AC/DC). When charged, a mechanical indicator on the front fascia shows "springs charged" and an auxiliary contact (S33M/2) signals the condition to the control system. Charging takes approximately 4–5 seconds with the standard motor.

Closing Sequence

When the closing command arrives — either via the front pushbutton, the shunt closing release (XF coil) or a remote signal through the Ekip Com communication module — a latch releases the stored spring energy. A four-bar linkage drives the moving contact arms downward against the fixed contacts. Total making time, from coil energization to contacts touching, is typically 70–80 ms.

Opening Sequence

Opening can be commanded three ways: the front trip pushbutton (mechanical), the shunt opening release (YO coil, fed from the trip unit or external signal), or the undervoltage release (YU coil, which trips when its supply falls below 35–70% of nominal). The opening springs — separate from the closing springs — drive the contacts apart in roughly 25–30 ms. Add 10–15 ms for arc extinction in the chute and you arrive at the catalog total break time of around 40 ms.

How Does the Ekip Trip Unit Sense and Decide?

The brain of every ABB Emax 2 is an Ekip electronic trip unit. Unlike older thermal-magnetic releases, the Ekip uses Rogowski coil current sensors and a microprocessor running protection algorithms at high sampling rates. There is no thermal bimetal involved — all "long-time" behavior is simulated in firmware.

Current Sensing with Rogowski Coils

Each pole carries a Rogowski coil — a coreless toroidal winding — around its primary conductor. Because there is no iron core, the coil cannot saturate, so it remains accurate from a few amperes up to the full short-circuit withstand. The coil output is an EMF proportional to di/dt, which the trip unit integrates digitally to recover the true current waveform.

Protection Functions: L, S, I, G

The standard Ekip Dip variant — found in units like the ABB 1SDA070741R1 E1.2B 800 Ekip Dip LI — provides L (long-time overload) and I (instantaneous short-circuit) protection. Higher tiers add S (short-time delayed) and G (ground fault), as in the ABB 1SDA070782R1 E1.2B 1000 Ekip Dip LSI. Engineers often overlook that the LSI configuration is what enables true time-current selectivity with downstream MCCBs — pure LI breakers cannot grade against fast downstream faults.

Decision Time

For an instantaneous trip (I), the Ekip processor evaluates each half-cycle. From fault inception to trip command at the YO coil, decision time is typically 8–10 ms. The mechanism then takes another 25–30 ms to open the contacts. End-to-end clearing time at I3 pickup is roughly 35–40 ms — fast enough to limit let-through I²t for downstream cable protection.

How Does Arc Interruption Work Inside the Arc Chute?

This is where the air circuit breaker earns its name, and it is central to how the ABB Emax 2 performs under fault conditions. When the contacts separate under load, an arc forms across the gap. At 415 V and 50 kA prospective, that arc carries enormous energy and must be extinguished within one or two half-cycles, otherwise the breaker — and the switchboard around it — will not survive.

The Emax 2 uses the classic deion arc-chute principle. As the moving contact lifts, magnetic blowout forces (from the current loop itself) drive the arc upward into a stack of steel splitter plates. The plates split the arc into many short arcs in series. Each short arc has a cathode-anode voltage drop of roughly 25–30 V; with 30+ plates, the total arc voltage exceeds the system driving voltage, forcing the current to zero at the next natural zero crossing. Once at zero, the de-ionized air in the chute prevents re-ignition.

In practice, what we typically see in the field is that arc-chute integrity is the single most common reason a refurbished Emax breaker fails its routine test. After interrupting a near-rated short circuit, the splitter plates erode and the side walls accumulate metallic deposits. ABB recommends inspection after every short-circuit interruption greater than 50% of Icu.

How Do Selectivity and Zone Selective Interlocking Work?

A common mistake on greenfield projects is to set every breaker to its factory defaults and assume the manufacturer has solved selectivity. It hasn't. Time-current grading is your responsibility, and the ABB Emax 2 gives you two tools.

Time-Current Grading

With LSI trip units, you set the upstream Emax to a longer S (short-time) delay than the downstream device. For example: a transformer incomer E2.2B 1600 with Ekip Dip LI would not grade well — it has only instantaneous. You would instead specify an Ekip Touch LSI version and set t2 = 200 ms while the downstream feeder Emax sits at t2 = 100 ms. The 100 ms gap accounts for breaker opening time plus a safety margin.

Zone Selective Interlocking (ZSI)

For installations where you cannot accept the 200 ms upstream delay — data centers, hospitals, semiconductor fabs — ZSI is the answer. Each Ekip trip unit has a ZSI-IN and ZSI-OUT terminal. When a downstream breaker detects a fault, it sends a blocking signal upstream within 4 ms. The upstream Emax, on receiving the block, holds at its long S-delay. If no block arrives, the upstream Emax interrupts immediately at a short delay (typically 80 ms) regardless of its t2 setting. This gives you both selectivity and fast clearance — particularly relevant for the architectures described in our piece on Emax 2 in data center MDB design.

How Do Communication and Power Management Work?

The ABB Emax 2 was the first ACB to embed power metering as a standard feature rather than an add-on. The Ekip Touch and Ekip Hi-Touch trip units measure voltage (via internal taps), current (via the Rogowski coils), and compute kW, kVAR, kVA, power factor, THD up to the 40th harmonic, and energy in kWh — all to revenue-grade Class 1 accuracy per IEC 61557-12.

Communication modules clip onto the back of the trip unit. The Ekip Com Modbus RTU module is the most common in industrial sites; Ekip Com Profibus, Modbus TCP, EtherNet/IP, IEC 61850 and Profinet are all available. In our experience, IEC 61850 is increasingly specified on utility and renewable substation projects in Europe — confirm protocol requirements at tender stage, because retrofitting a different module may require a firmware update.

How Do You Specify and Size an Emax 2 Correctly?

Sizing an ABB Emax 2 involves three parallel checks: continuous current, short-circuit withstand and short-circuit breaking. Get any one wrong and the breaker is unsafe or non-compliant.

Continuous current (In) must exceed the calculated load current with appropriate diversity, derated for ambient temperature above 40 °C. For a 1000 kVA transformer at 400 V, secondary full-load is 1443 A — you would specify an E1.2B 1250 only if you accept overload protection at slightly below FLA, or step up to an E1.2B 1600. The detailed methodology, including ambient correction tables, is laid out in our Emax 2 sizing calculator guide.

Performance Class Comparison

What Goes Wrong in the Field, and Why?

In twenty years of commissioning ABB Emax 2 breakers, three failure modes dominate. First: nuisance tripping on long-time, almost always caused by undersized breakers on harmonic-rich loads (VFDs, UPS rectifiers). The Ekip computes true RMS, so it correctly trips on real heating current — but the designer used apparent fundamental current. Our diagnostic walkthrough on Emax 2 nuisance tripping causes covers this in detail.

Second: contact wear after frequent operation. Emax 2 is rated for 12,500 mechanical operations and 10,000 electrical operations at In on E1.2 frames. If you are switching the breaker daily for load shedding, you will reach end-of-life in about 27 years — but at hourly switching, less than two years. Some engineers argue contactors should be used for frequent switching, and in my experience that is correct below 800 A, where an AF-series contactor handles the duty better.

Third: trip unit firmware mismatches after spare swaps. Always verify that the Ekip firmware matches the installed CT ratio plug — a wrong rating plug on the same trip unit electronics produces silently incorrect protection. Browse the full Air Circuit Breakers range at Stoklink for compatible spares, and our Relay collection for auxiliary protection.

Related Reading

• What Is the ABB SACE Emax 2? Features, Models and Key Benefits
• ABB Emax 2 Full Technical Specifications: Current Ratings, Breaking Capacity and Dimensions
• ABB Emax 2 vs Schneider MasterPact MTZ: Technical Specs, Features and Price Compared
• How to Size ABB Emax 2: Step-by-Step Calculator for LV Distribution Panels

Conclusion

The ABB SACE Emax 2 is a deceptively complex piece of engineering. On the outside it looks like any other ACB; inside, it combines a refined stored-energy mechanism, coreless Rogowski sensing, a microprocessor-based trip unit and a passive deion arc chute that has to handle up to 200 kA in a few milliseconds. Understanding how each subsystem works — the spring linkage, the trip algorithm, the splitter plates, the ZSI bus — is what separates a competent specification from a generic one. Specifying the right frame, the right performance class, and the right Ekip variant for the application is not a catalog exercise; it is a protection coordination study, a thermal study and a duty-cycle assessment combined.

For procurement teams, the practical advice is straightforward: confirm the frame, performance class (B/N/H/V), trip unit family, communication module and accessory pack at the order stage, because field upgrades cost more than the original premium. Stoklink stocks the full standard configuration range, including the ABB 1SDA070781R1 E1.2B 1000 and ABB 1SDA071021R1 E2.2B 2000 for fast delivery. For complementary protection and control devices, see our Miniature Circuit Breaker and Residual Current Device collections.

For the full selection methodology, lifecycle planning and application case studies, see our ABB SACE Emax 2 selection, application and maintenance guide — the parent reference for everything covered here and across the Emax 2 article series.