ABB SACE Emax 2 in MV LV Main Switchboards for Industrial Plants

What is an ABB SACE Emax 2 in MV/LV main switchboards? An ABB SACE Emax 2 is an open-air low-voltage circuit breaker rated 400–6300 A up to 1000 V AC under IEC 60947-2, deployed as the principal incomer, bus-tie, or feeder breaker in main distribution boards fed from medium-voltage transformer secondaries. Undersizing the frame for transformer inrush, miscalculating selectivity ratios, or omitting IEC 61439-compliant busbar ratings risks cascading trips, transformer damage, and unplanned plant shutdowns. This guide covers Emax 2 frame selection against transformer secondary current, time-current selectivity strategy in industrial MDBs, bus-tie and dual-transformer switching configurations, outgoing feeder matching, and SCADA integration via IEC 61850 or Modbus.

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

Why the Emax 2 Dominates Industrial Main Switchboards

Walk into any modern cement plant, automotive paint shop, or pharmaceutical clean utility room built in the last decade, and you will almost certainly find an ABB Emax 2 sitting as the LV incomer of the main distribution board (MDB). There is a reason for that. The Emax 2 covers a continuous current range from 630 A up to 6300 A in four mechanical sizes (E1.2, E2.2, E4.2, E6.2), which lets a panel builder standardize on one breaker family from a 1000 kVA distribution transformer all the way to a 4000 kVA unit substation feeding a steel rolling mill.

In our experience, the value of the Emax 2 in an industrial MDB is not the breaker itself — it is what the Ekip trip unit does. A typical incomer in a 2500 kVA, 400 V transformer secondary draws around 3600 A full load. You can cover that with an ABB 1SDA071021R1 E2.2B 2000 Ekip Dip LI only if you derate; in reality you go up to E4.2 4000. But for the bus-tie, secondary feeders to MCCs, and large motor groups, the E1.2 and E2.2 frames cover most of what an industrial plant actually needs.

The MV/LV Interface Question

Engineers often overlook that the Emax 2 sits on the LV side of the transformer, not at the MV interface. The MV breaker (typically a vacuum circuit breaker in the 12 kV or 24 kV switchgear) handles transformer primary protection. The Emax 2 handles secondary overcurrent, ground fault, and — critically — provides the disconnection point for maintenance on the LV bus. The coordination between the MV protection relay (often a SEPAM, REF615, or similar IED) and the LV Emax 2 trip unit is where most selectivity headaches happen.

A common mistake is assuming the LV breaker will always clear a fault before the MV relay sees it. Not always. For a bolted fault on the LV busbar, the MV relay may pick up via the transformer reflected impedance in 40–60 ms, while the Emax 2 short-time delay (S protection) is set at 200 ms for selectivity with downstream MCCBs. If you do not coordinate these, you trip the entire MV feeder for an LV fault — and in a process plant that means hours of restart.

For complete technical specifications and application data on the ABB Emax 2 air circuit breaker family, refer to the ABB SACE Emax 2 product documentation, which details frame ratings, Ekip trip unit configurations, and compliance with IEC 60947-2.

Sizing the Emax 2 for the Transformer Secondary

The first sizing question is straightforward: what is the transformer full-load current, and what continuous rating do you need on the breaker? The second question — and the one that catches procurement off guard — is what is the prospective short-circuit current at the LV bus, and does the ABB Emax 2 frame's Icu rating cover it with margin?

For a 1600 kVA, 400 V transformer, that gives 2309 A. You would specify an Emax 2 with at least 2500 A continuous rating — in practice the E2.2B 2000 A is undersized; you go E4.2 2500 or 3200. For an 800 kVA unit substation feeding a smaller plant section, full-load is 1155 A, and the ABB 1SDA070821R1 E1.2B 1250 fits cleanly.

For a 2500 kVA transformer with uk = 6%, the LV bus prospective Ik" is roughly 60 kA. The Emax 2 E2.2B has Icu = 42 kA at 415 V — not enough. You move to the E2.2N (66 kA) or E2.2H (85 kA). Procurement managers regularly push for the lower-rated B variant to save 15–20% on price; in our experience, this is short-sighted because a single retrofit later costs ten times the saving. For detailed sizing logic with a worked example, the step-by-step Emax 2 sizing calculator guide is the right reference.

Selectivity Strategy in Industrial MDBs

This is where the ABB Emax 2 earns its place. Selectivity in an industrial plant is not optional — when a fault occurs in a single MCC, you cannot afford to trip the entire 4 MW production line. The Ekip Dip and Ekip Touch trip units provide L-S-I-G protection (long-time, short-time, instantaneous, ground fault) with the time-current curves needed to coordinate with downstream MCCBs like Tmax XT and molded-case devices.

The S-Protection Band

The short-time protection (S) on the Emax 2 is the workhorse for selectivity. Typical settings on an incomer: I2 = 6 × In, t2 = 200–400 ms. This gives downstream MCCBs in the 400–630 A range time to clear their faults via instantaneous trip (typically 30–50 ms total clearing time including breaker operating time). For the bus-tie or feeders to large MCCs, you might use an ABB 1SDA070981R1 E2.2B 1600 Ekip Dip LI with intermediate S settings to create a third selectivity tier.

What we typically see in the field: panel builders set every Emax 2 to factory defaults and call it commissioned. That is not selectivity — that is a coincidence. Real selectivity requires a coordination study with curves drawn at 415 V, with motor inrush envelopes overlaid, and with the Ekip parameters set per breaker. ABB's eDesign software does this; so does ETAP. There is no shortcut.

The Bus-Tie and Two-Transformer Configurations

Most industrial plants of any size run two transformers in a main-tie-main configuration with the bus-tie normally open. When one transformer is lost, the bus-tie closes and the remaining transformer carries the full plant load. This sounds simple. In practice the ABB Emax 2 selection for the bus-tie is a topic engineers argue about for hours.

The bus-tie sees the full short-circuit contribution from both transformers (when paralleled momentarily during transfer) and must carry the full load of the larger transformer. For two 2000 kVA transformers, the tie typically uses the same frame as the incomers — say an E4.2 3200. Some engineers argue you can downsize the tie because it rarely carries continuous load; others insist on equal sizing for symmetry. In my experience, equal sizing wins: the small saving from a smaller tie is not worth the spare-parts complexity, and during long-duration single-transformer operation the tie carries continuous load.

Closed Transition vs Open Transition

Open transition (break-before-make) is standard and safe. Closed transition (make-before-break, with both transformers paralleled for ~100 ms) requires the Emax 2 to handle the parallel short-circuit current, which can double Ik". If you specify closed transition, verify the Icu rating against the parallel scenario, not the single-transformer case. This is where many designers get caught — they size for normal operation and forget the transition window.

Outgoing Feeders: Matching Emax 2 Frames to Loads

Below the incomer and bus-tie, the outgoing feeders to sub-distribution boards, MCCs, and large single loads are where the smaller ABB Emax 2 frames shine. A typical 1000 kW motor at 400 V draws about 1750 A — too large for an MCCB, ideal for an ABB 1SDA070861R1 E1.2B 1600 Ekip Dip LI with motor protection settings on the Ekip unit, or for an E2.2 if margin is needed for starting.

For sub-distribution feeders to MCCs in the 500–800 A range, the ABB 1SDA070741R1 E1.2B 800 and ABB 1SDA070701R1 E1.2B 630 are common choices. They give you the same Ekip platform as the incomer — same communication, same diagnostics, same parameter language — which simplifies commissioning and operator training.

When to Specify LSI vs LI Trip Units

The LI variant (long-time + instantaneous) is sufficient for radial feeders to single loads. The LSI variant (long-time + short-time + instantaneous), such as the ABB 1SDA070782R1 E1.2B 1000 Ekip Dip LSI, is required wherever you need selectivity below the breaker — that is, on every feeder going to a sub-distribution board with its own breakers downstream. The price difference is small. The functional difference is significant. Always specify LSI for sub-distribution feeders.

Communication and Plant SCADA Integration

Modern industrial plants run on Modbus TCP, Profibus, or Profinet for switchgear monitoring. The ABB Emax 2 with Ekip Com modules covers all of these. In a typical paper mill or chemical plant, the MDB is monitored by the plant DCS — every breaker reports status, current per phase, energy consumption, trip causes, and contact wear. This data is what enables condition-based maintenance instead of time-based maintenance.

The practical setup: each Emax 2 has an Ekip Com Hub or Ekip Com Modbus TCP module, all connected to a panel-mounted gateway, which talks to the DCS. From the control room, an operator can see that the bus-tie has cycled 47 times this year, that the incomer has accumulated 12% contact wear, and that phase B current is running 8% higher than phase A — a sign of an unbalanced load that needs investigation before it becomes a fault. For data center applications where this monitoring is mission-critical, the considerations are slightly different, as covered in the data center MDB design guide.

Coordination with Standards: IEC, IEEE, and NEMA

For global industrial projects, the standards landscape matters because the same plant may have IEC-compliant European equipment, IEEE-compliant American documentation, and NEMA-rated panels. The ABB Emax 2 is tested and certified to IEC 60947-2 (general LV switchgear), IEC 60947-1 (general rules), and UL 1066 (LV power circuit breakers used in enclosures) for North American markets. This dual certification is one of the reasons the Emax 2 ends up in plants from Houston to Shanghai.

Per IEC 60947-2 §8.3.4, the Icu (ultimate breaking capacity) is the value the breaker can interrupt once and survive for inspection; Ics (service breaking capacity) is what it can interrupt repeatedly without degradation. For industrial MDBs, always check Ics — for the Emax 2 the Ics is generally 100% of Icu, which is a real advantage over many MCCBs where Ics is 50–75% of Icu. NEMA AB 4 covers field testing of the breaker after installation, and IEEE C37.13 covers low-voltage AC power circuit breakers used in enclosures, which aligns closely with how the Emax 2 is applied in North American switchgear.

Procurement Considerations and Common Pitfalls

From a procurement perspective, the ABB Emax 2 selection often comes down to availability and lead time. ABB's manufacturing lead times for standard E1.2 and E2.2 frames are typically 6–10 weeks; for E4.2 with Ekip G Hi-Touch trip units, lead times can stretch to 16–20 weeks. For brownfield retrofit projects, this is the single biggest schedule driver. Holding strategic spares of the most-used frames at the panel builder or end-user warehouse is standard practice in industries where downtime costs exceed €10,000/hour.

A second pitfall: ordering the breaker without the right accessories. The Emax 2 needs a closing coil (YC), at least one shunt trip (YO), an undervoltage release (YU) if required by the application, motor operator (M), and auxiliary contacts (AUX). Specifying these after the fact means weeks of delay. Specify the full configuration code at the start. For comparison with the closest competitor, the Emax 2 vs Schneider MasterPact MTZ comparison goes through this in detail.

Maintenance and Lifecycle Considerations

The ABB Emax 2 is rated for 20,000 mechanical operations and 10,000 electrical operations at full load (E1.2 and E2.2 frames). For an MDB incomer that operates a few times per year, this is essentially "lifetime" — but for a bus-tie that cycles weekly during transformer maintenance rotation, or for a tie breaker in an automatic transfer scheme, you can accumulate a thousand operations in five years. Track them. The Ekip trip unit has an internal counter that reports operations and percentage of contact wear; ignoring this counter is one of the most common maintenance failures we see in audits.

Preventive maintenance per IEC 61439-2 and the ABB maintenance manual calls for a visual inspection at 12 months, a functional test at 24 months, and a full overhaul (contact inspection, mechanism lubrication, secondary wiring check) at 5 years or 5000 operations, whichever comes first. In a process plant where the MDB is a stranded asset — meaning you cannot easily de-energize it — these intervals slip. They should not. A breaker that has not been operated in 8 years has a measurable risk of mechanism seizure on first demand, and that demand is usually a fault condition.

Nuisance Tripping in the Field

One pattern that comes up repeatedly in industrial commissioning: the Emax 2 trips on long-time protection (L) during process startup, even though steady-state current is well within rating. The cause is almost always thermal memory — the Ekip trip unit remembers prior loading, and a hot restart after a brief shutdown trips earlier than a cold start would. Engineers see this and immediately blame the breaker. It is not the breaker; it is the protection algorithm doing exactly what IEC 60947-2 expects. The fix is parameter adjustment, not hardware replacement. The diagnostic process is covered in detail in the article on Emax 2 nuisance tripping root causes and fixes.

Real-World Application: 6 MW Industrial Plant Example

To make this concrete, consider a typical mid-size industrial plant — a food processing facility with 6 MW installed load, two 4000 kVA MV/LV transformers (20 kV / 400 V, uk = 6.25%) in main-tie-main configuration, each protected by an ABB Emax 2 incomer. The full-load current per transformer is 5774 A. Prospective Ik" at the LV bus, with both transformers paralleled briefly during transition, reaches 132 kA.

The breaker selection logic plays out like this. Each incomer is an Emax 2 E6.2 6300 with Ekip Hi-Touch LSIG trip unit, Icu = 150 kA at 415 V. The bus-tie matches: E6.2 6300, Icu = 150 kA. Outgoing feeders to the seven main MCCs — each rated 600–1200 A — use a mix of ABB 1SDA070781R1 E1.2B 1000, E1.2B 1250, and E1.2B 1600 frames with Ekip Dip LSI trip units. Two large refrigeration compressors at 1.5 MW each are protected by ABB 1SDA070981R1 E2.2B 1600 frames with motor protection settings.

Selectivity is achieved through three time-bands: incomer S at 400 ms, MCC feeders S at 200 ms, downstream MCCBs instantaneous. Ground fault is set on the incomer at 1200 A pickup, 400 ms delay, and on each MCC feeder at 600 A, 200 ms — a classic two-tier ground fault scheme that prevents single ground faults from tripping the entire plant. All breakers report to the plant DCS via Modbus TCP through the Ekip Com Hub. The total cost of the LV switchgear breakers is roughly 8% of the MDB project value, but their selection drives 60% of the engineering effort. That ratio is typical for industrial main switchboards. For a deeper dive into the Emax 2 model range and how to navigate it, the Emax 2 features and models overview is the right starting point, and the full technical specifications guide covers ratings and dimensions in detail.

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
• How to Size ABB Emax 2: Step-by-Step Calculator for LV Distribution Panels
• ABB Emax 2 in Data Centers: MDB Design, Redundancy and Uptime Considerations

For a broader range of LV protection devices commonly applied alongside the Emax 2 in industrial MDBs, see the Stoklink collections for air circuit breakers, miniature circuit breakers, residual current devices, and protection relays.

Conclusion

The ABB SACE Emax 2 has become the default LV circuit breaker for industrial main switchboards because it solves the right combination of problems: wide current range from one product family, high breaking capacity in a compact footprint, integrated metering and communication via the Ekip platform, and dual IEC/UL certification for global projects. Specifying it well requires more than picking a frame and a current rating. It requires a transformer impedance calculation, a selectivity study, an accessory configuration, and a maintenance plan — all done before the panel builder cuts steel.

The plants that get this right have main switchboards that ride through faults, restart cleanly, and run for 25 years with predictable maintenance. The plants that treat the Emax 2 as a commodity end up with selectivity problems, nuisance trips, and emergency procurement at three times the price. The difference is engineering judgment applied at specification time. For the complete selection methodology including frame selection, trip unit configuration, accessory specification, and maintenance planning, see the ABB SACE Emax 2 selection, application and maintenance guide, and for the broader context of LV power switching technology, the air circuit breaker engineering guide covers the underlying principles that apply across the Emax 2 range and beyond.