ABB SACE Emax 2 Air Circuit Breaker: Complete Technical Guide
What is the ABB SACE Emax 2? The ABB SACE Emax 2 is a draw-out or fixed air circuit breaker rated 400–6300 A at up to 1000 V AC under IEC 60947-2, with ultimate breaking capacities reaching 150 kA and a short-time withstand rating that supports selective coordination in large LV switchboards. Misapplying the Emax 2 — confusing Icu with Ics, undersizing Icw for busbar-protection schemes, or misconfiguring the Ekip trip unit — risks failed selectivity, thermal damage, or non-compliant protection grading. This guide covers current-interruption mechanics, the meaning of Icu/Ics/Icw ratings, Ekip trip-unit functionality, panel sizing methodology, and application limitations.
What is the ABB SACE Emax 2 and where does it fit?
The Emax 2 sits at the top of ABB's LV breaker portfolio, above the Tmax XT moulded-case range. It replaces the original Emax (sometimes called Emax 1) launched in the late 1990s, and the architectural difference is significant: Emax 2 was built around the Ekip trip unit platform from day one, so the data, communication and protection layers were not bolted on — they share silicon.
In our experience, this matters most in two scenarios. First, in main distribution boards (MDBs) feeding multiple downstream feeders where selectivity must be coordinated to within 50 ms. Second, in facilities pursuing ISO 50001 energy management, where the breaker is expected to log power, energy and harmonic distortion without a separate meter.
Frame sizes and the naming logic
Emax 2 uses four mechanical frames: E1.2, E2.2, E4.2 and E6.2. The number after the dot is not a version — it indicates the second-generation Emax. Within each frame, ABB offers performance classes (B, N, S, H, V, X, L) that describe breaking capacity rather than current rating. So an ABB 1SDA070701R1 E1.2B 630 Ekip Dip LI is an E1.2 frame, B class (42 kA Icu at 415 V), with a 630 A rated current and a basic LI (Long-time + Instantaneous) trip unit.
A common mistake during procurement is to specify only the current rating. Two breakers labelled "1600 A" — the E1.2B 1600 (1SDA070861R1) and the E2.2B 1600 (1SDA070981R1) — have the same In but very different mechanical endurance and busbar geometries. The E2.2 is the right choice when the same 1600 A feeder is expected to operate as a tie breaker with frequent switching duty.
For complete protection settings, breaking capacity tables and accessory compatibility, refer to the ABB SACE Emax 2 technical catalogue available through the ABB Emax 2 product documentation, which aligns with IEC 60947-2 type-test data.
How does the Emax 2 actually break current?
An ACB extinguishes a fault current by forcing the arc upward into a stack of steel splitter plates. The arc gets divided into many short arcs in series; each segment requires a minimum arc voltage to sustain ionisation. When the cumulative arc voltage exceeds the system driving voltage, current is forced to zero and the arc dies at the next natural zero crossing.
That sounds simple. It is not. The dynamics depend on contact velocity, magnetic blow-out fields generated by the current itself, and the gas pressure produced by ablation of the arc-runner material. In a 50 kA test at 415 V, the entire sequence — from contact separation to current zero — takes about 8 to 12 ms. For a deeper view of the mechanism, see how the ABB Emax 2 works: arc quenching, trip units and operation.
Why two contact systems?
Emax 2 uses an arcing contact (tungsten-based, sacrificial) and a main contact (silver-alloy, low resistance). The arcing contact opens last and closes first. This protects the main contact from erosion. After roughly 10 000 mechanical operations or 10 full-rated short-circuit interruptions, the arcing contacts should be inspected — IEC 60947-2 §8.3.6 references the operation cycles defining electrical endurance.
Ratings: what do Icu, Ics and Icw really mean?
Engineers often overlook the difference between these three ratings, and procurement teams sometimes use them interchangeably in tender documents. They are not interchangeable.
- Icu — ultimate breaking capacity. The breaker must interrupt this current once and remain safe, but not necessarily reusable.
- Ics — service breaking capacity. After interrupting Ics, the breaker must remain fully serviceable. Often expressed as a percentage of Icu (e.g., 100% Ics = Icu).
- Icw — short-time withstand current. The current the breaker can carry for 1 s (or 3 s) without tripping, enabling time-based selectivity with downstream devices.
The Icw is what makes an ACB an ACB. A 1600 A Tmax XT moulded-case might match an Emax 2 on Icu, but its Icw is a fraction of the value. For a transformer secondary feeder where a downstream MCCB needs 200 ms to clear a fault, only an ACB with Icw ≥ 42 kA for 1 s will hold its position long enough to allow discrimination.
Formula: Peak short-circuit current (Ipk) — Source: IEC 60947-2 Annex G
Ipk = n × Icu
| Symbol | Description | Unit |
|---|---|---|
| Ipk | Peak prospective short-circuit current | kA |
| Icu | Ultimate RMS breaking capacity | kA |
| n | Asymmetry factor (typ. 2.1 for cos φ = 0.2 at 50 kA) | — |
Class B vs Class N vs Class H: a procurement view
| Criteria | E1.2 Class B | E2.2 Class N | E4.2 Class H |
|---|---|---|---|
| Icu @ 415 V | 42 kA | 66 kA | 100 kA |
| Ics | 100% Icu | 100% Icu | 100% Icu |
| Icw (1 s) | 42 kA | 66 kA | 85 kA |
| Max In | 1600 A | 2500 A | 4000 A |
| Typical use | Sub-distribution, gen feeders | MDB incomer ≤ 2.5 MVA | MDB incomer 3–4 MVA, parallel sources |
For full ratings tables across all eight classes, the Emax 2 technical specifications guide is the right reference.
The Ekip trip unit: where the intelligence lives
The Ekip family ranges from Ekip Dip (mechanical-style DIP-switch settings, no display) to Ekip Hi-Touch (full colour HMI, IEC 61850 communication, IEEE 1588 PTP time sync). The naming after "Ekip" describes the protection functions:
- LI — Long-time + Instantaneous (basic feeder protection)
- LSI — adds Short-time (enables zone-selective interlocking)
- LSIG — adds Ground-fault
- LSIRc — adds Residual current
In practice, what we typically see in the field is over-specification on the trip-unit side and under-specification on the frame. A facility manager will request Ekip Hi-Touch with full IEC 61850, then size the breaker on nameplate current without considering future load growth. The trip unit is field-replaceable; the frame is not. Specify the frame for 20-year load forecasts; specify the trip unit for today's monitoring needs.
The LSIG protection curve, explained
The four-zone LSIG curve (Long-time, Short-time, Instantaneous, Ground-fault) is what makes selective coordination possible in a five-tier distribution system. The L pickup (typically 0.4–1.0 × In) protects against thermal overload using an I²t algorithm. The S pickup (1–10 × In) handles short-circuits with a definite-time delay (50–800 ms). The I pickup (1.5–15 × In) provides instantaneous trip with no intentional delay — usually 30–50 ms total clearing time including mechanical operation.
How to size an Emax 2 for an LV panel
Sizing is more than picking a current rating above the load. The four constraints are: rated current (In), breaking capacity (Icu/Ics), short-time withstand (Icw) and pole arrangement (3P or 4P). Here is the field methodology we use.
- Calculate the maximum continuous load — typically 1.25 × full-load amps for motor feeders per IEEE 141 §3.5.
- Determine the prospective short-circuit current (Ik) at the breaker location. This requires the transformer impedance, cable impedance and source impedance.
- Select a frame whose Icu ≥ Ik with at least 20% margin for future growth.
- Verify Icw ≥ Ik for the selectivity time required by downstream protection.
- Confirm pole count: 4P required where the neutral carries harmonic currents (typical in data centers, LED lighting loads).
For a worked walkthrough including selectivity calculations, see how to size ABB Emax 2: step-by-step calculator for LV distribution panels.
Real example: 2 MVA transformer feeder
A 2000 kVA, 400 V Dyn11 transformer with 6% impedance produces a full-load current of 2887 A and a prospective Ik of about 48 kA. Typical selection: ABB 1SDA071021R1 E2.2B 2000 Ekip Dip LI — an E2.2 frame, B class (66 kA Icu margin over the 48 kA fault), 3000 A In. The B class gives 18 kA margin, which is comfortable. Going to N class buys nothing here. Going to A class (lower) leaves only 4 kA margin — too tight.
Where does Emax 2 perform well, and where does it struggle?
Emax 2 is the default choice for LV main distribution boards from 630 A up to 6300 A. It performs especially well in:
- Data centers — withdrawable execution allows live replacement of a faulty breaker without de-energising the busbar. See Emax 2 in data centers: MDB design, redundancy and uptime considerations.
- Marine and offshore — units tested per IEC 60092-504 are available, with vibration and salt-spray tolerance.
- Industrial plants with multiple parallel transformers and tie breakers, where Icw above 65 kA for 1 s is required.
It is not the right choice for:
- Small panels under 630 A — a Tmax XT MCCB is cheaper and more compact.
- DC applications above 1000 V — the Emax DC variant exists but is a different product line.
- High-frequency switching duty (more than 50 operations per day) — the mechanism, while robust, is not designed for contactor-style duty. Use an ABB AF contactor for that.
Common failure modes and what causes them
From our service records across roughly 400 Emax 2 installations, here are the issues we see most often.
Nuisance tripping
The number-one call. About 70% of nuisance trips trace to incorrect L pickup setting (set too close to actual load) or to harmonic distortion that the trip unit's RMS sensing reports correctly but the engineer interprets as "just" the fundamental. The Ekip Touch displays THD; engineers should look at it before raising the pickup. For a full diagnostic flow, see Emax 2 nuisance tripping: root causes, diagnostic steps and fixes.
Failed close coil after long idle periods
Breakers stored closed but unoperated for over 12 months sometimes fail to close on first attempt. The cause is mechanical stiction in the closing latch, not the coil. IEC 60947-2 §B.8.1 recommends operational tests every 6 months. We see this most in standby switchboards for emergency generators.
Trip-unit communication loss
On Modbus RTU networks, communication failures usually trace to termination resistors (missing or doubled) and incorrect baud-rate settings rather than to the Ekip module itself. Always check the physical layer first.
Emax 2 vs the competition
The natural comparison is Schneider Electric MasterPact MTZ. Both are mature, IEC 60947-2 compliant, withdrawable ACBs with intelligent trip units. The differences are subtle but matter for procurement standardisation:
- Emax 2 has a wider Ekip Dip range (basic mechanical-feel trip units), useful where the customer wants no firmware in the protection path.
- MasterPact MTZ Micrologic X uses a digital module structure with field-loadable apps; Ekip uses fixed-function modules.
- Emax 2 supports IEC 61850 Edition 2 natively on Hi-Touch; MasterPact requires the IFE gateway.
For a side-by-side technical and commercial comparison, see ABB Emax 2 vs Schneider MasterPact MTZ: technical specs, features and price compared.
Installation, accessories and procurement notes
An ACB is rarely bought naked. The typical order includes the breaker, a cradle (for withdrawable execution), motor operator, closing/opening coils, undervoltage release, auxiliary contacts, and trip-unit accessories. ABB's catalogue numbering is dense; mistakes cost weeks. Always cross-check the SKU against the catalogue's selection table.
For 1000 A feeders requiring zone selectivity, the 1SDA070782R1 E1.2B 1000 Ekip Dip LSI is preferable to the LI variant; the S element is what enables time-graded discrimination with downstream MCCBs.
Stoklink stocks the full Emax 2 range alongside complementary protection devices — see our air circuit breakers, miniature circuit breaker, residual current device and relay collections.
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Frequently Asked Questions
What does "Emax 2" mean — is it different from Emax?
Emax 2 is the second-generation Emax platform, launched by ABB SACE in 2014. It shares the conceptual architecture of the original Emax (introduced in the late 1990s) but with a redesigned mechanism, smaller footprint and the Ekip trip-unit family built in. They are not interchangeable: cradles, trip units and accessories are not backward-compatible.
Is the Emax 2 IEC and UL certified?
The standard Emax 2 is tested and certified to IEC 60947-2. A separate UL-listed variant — Emax 2 UL — exists for North American projects, certified to UL 1066 and built with NEMA-compliant terminals. The two ranges share the mechanism but differ in electrical clearances and creepage distances. Don't assume an IEC unit can be installed in a UL-listed switchboard.
How often should an Emax 2 be maintained?
ABB recommends a visual inspection every 12 months and a full mechanical service every 5 years or 5 000 operations, whichever comes first. In dusty or corrosive environments (cement plants, coastal sites) we shorten the interval to 6 months. The arcing contacts should be checked after every full-rated short-circuit interruption per IEC 60947-2 §8.3.6.
Can I retrofit an Ekip Touch trip unit onto an existing Emax 2 with Ekip Dip?
Yes. The trip unit is field-replaceable on the same frame. You'll need the matching Ekip Touch module, the appropriate current-sensor harness if upgrading from LI to LSIG, and a brief commissioning to load the protection settings. This is one of the strongest arguments for choosing Emax 2 over a fixed-function competitor — see how the Emax 2 trip-unit architecture works for the upgrade path.
What is the difference between fixed and withdrawable Emax 2?
A fixed breaker is permanently bolted into the switchboard busbar. A withdrawable breaker plugs into a cradle and can be racked out to test or isolated positions without de-energising the busbar. Withdrawable adds about 20% to cost and 80 mm to depth but reduces mean-time-to-repair from hours to minutes. For mission-critical loads — data centers, hospitals, process plants — withdrawable is the default.
Does the Emax 2 support IEC 61850 directly?
Yes, on the Ekip Hi-Touch and Ekip Touch with the Ekip Com IEC 61850 module. Edition 2 is supported, including GOOSE messaging for fast peer-to-peer signalling between breakers. This is the function that allows a 4 ms inter-breaker trip signal in zone-selective interlocking schemes — far faster than the 50–80 ms achievable over Modbus.
What's the typical lead time for ABB Emax 2 in stock?
Standard configurations — E1.2B and E2.2B with Ekip Dip LI — are usually held in stock by distributors. Higher classes (H, V, X, L) and Ekip Touch with custom communication modules typically run 6–10 weeks from ABB factories in Italy. For urgent projects, Stoklink maintains stock on the most-specified SKUs across the 630–2000 A range.
Conclusion: when to specify an Emax 2
The Emax 2 is the right answer when you need an LV breaker above roughly 800 A with high short-time withstand, integrated power monitoring, and a long service life under a defined maintenance regime. It is the wrong answer for small panels, contactor-style switching duty, or applications where a simpler MCCB will meet the fault-level requirement at half the cost.
The decisions that matter most — frame class, trip-unit family, fixed vs withdrawable, communication protocol — are made once and live with the asset for 25+ years. Take the time to model the fault levels, project the load growth, and specify around the worst-case selectivity scenario rather than today's nameplate. For the full selection methodology, including coordination studies and maintenance planning, refer back to the ABB SACE Emax 2 selection, application and maintenance guide.
For specific stock SKUs across the 630–2000 A range — including the E1.2B 800 (1SDA070741R1), E1.2B 1000 (1SDA070781R1) and E1.2B 1250 (1SDA070821R1) — the Stoklink air circuit breakers collection lists current availability and full configuration codes. If you're standardising a fleet across multiple sites, our engineering team can cross-reference legacy Emax 1 and competitor SKUs to the closest Emax 2 equivalent.
