ABB Emax 2 Withdrawable vs Fixed Version: Construction Compared

What is the difference between withdrawable and fixed ABB Emax 2 circuit breakers? The ABB Emax 2 withdrawable version is an IEC 60947-2-compliant air circuit breaker rated up to 6300 A in which the breaker cassette disconnects from fixed primary cradle contacts via a rack-and-pinion mechanism, enabling isolation and extraction without de-energising adjacent busbars, unlike the fixed version where primary terminals are bolted permanently to the switchboard. Specifying the wrong configuration — fixed where withdrawable is required — eliminates the ability to perform live-bus maintenance, forces full panel shutdown for breaker replacement, and can violate arc-flash safety procedures mandated by facility operating standards. This guide covers mechanical cradle and racking construction, primary and secondary circuit disconnection design, operational and maintenance workflow differences, IEC type-testing distinctions, and capital versus lifecycle cost trade-offs.

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

What Actually Differs Between Withdrawable and Fixed Emax 2?

On paper, the breaker pole assembly — the contacts, arc chutes, operating mechanism, Ekip trip unit — is identical between the two versions. ABB designs the ABB Emax 2 around a common circuit breaker module. Everything that changes lives outside that module: the cradle, the racking gear, the shutters, and the way the primary and secondary circuits make contact with the rest of the switchboard.

In a fixed (F) version, the breaker is bolted directly to the busbar via rigid copper terminals. Power connections are torqued and stay torqued. Auxiliary wiring lands on a fixed terminal block. To service the breaker you isolate upstream, padlock, verify dead, and only then can you reach the contacts.

In a withdrawable (W) version, the same breaker sits inside a cassette — a steel cradle with sliding cluster contacts, a racking screw, automatic safety shutters, and a separate plug for the secondary (control) circuit. You can move the breaker between three positions: connected, test, and isolated. Visible isolation in the isolated position satisfies IEC 60947-3 §7.1.7 requirements for an isolating function.

Why this distinction matters in real plants

A fixed Emax 2 like the ABB 1SDA070861R1 E1.2B 1600 Ekip Dip LI 3P 42 kA fixed typically takes 3–4 hours to replace if it fails: isolate the upstream main, lock-out, drop the busbar links, lift the unit out, install the spare, torque, megger, recommission. A withdrawable equivalent in the same E1.2B frame swaps in under 20 minutes, with only the local circuit dead during the change.

That is the trade-off in one sentence. You pay more capital up front for the cassette, and you buy back time when something goes wrong.

For complete technical specifications and type-test data on the ABB Emax 2 family, refer to ABB's official SACE Emax 2 technical catalogue and documentation, which details frame ratings, accessories, and compliance with IEC 60947-2.

Mechanical Construction Compared in Detail

The cassette of the withdrawable version

The ABB Emax 2 cassette is a self-contained chassis, available in the same frame sizes as the breaker (E1.2, E2.2, E4.2, E6.2). It carries six sliding cluster-contact assemblies for the main poles — silver-plated copper fingers loaded by stainless springs, designed for at least 500 mechanical insertions per IEC 60947-2 Annex M. The racking-in mechanism is a screw drive operated by a removable handle, not a lever. That choice is deliberate: a screw drive limits insertion speed, which prevents the operator from generating mechanical shock against the line-side cluster contacts.

Three positional interlocks exist on the cassette:

The first prevents racking while the breaker is closed — you cannot drive the contacts apart under load. The second prevents closing when the breaker is between defined positions. The third is an optional key interlock (Castell or Ronis) for procedural lock-out. Engineers often overlook the second one, and I have seen commissioning teams in petrochemical projects fight false "trip on close" indications that turned out to be a half-racked cassette.

The fixed version's bolted terminals

Fixed Emax 2 versions use horizontal or vertical bolted terminals — typically M12 or M16 depending on frame. The ABB 1SDA070701R1 E1.2B 630 fixed uses M12 with a recommended torque of 70 Nm per the ABB installation manual 1SDH001000R0002. Get the torque wrong and you get hot joints; that is the biggest single cause of nuisance heating in fixed installations and a frequent topic in our Emax 2 nuisance tripping diagnostic guide.

Footprint and panel impact

A withdrawable cassette adds roughly 90–120 mm depth and about 60 mm height to the breaker module. For an E2.2 frame that means the panel cell grows from approximately 324 mm × 302 mm × 395 mm (fixed) to 404 mm × 364 mm × 480 mm (withdrawable). In a data center where every rack-meter of the main distribution board is fought over — see our piece on Emax 2 in data center MDB design — that extra volume is not free. It can push you from a single-stack to a double-stack switchgear lineup.

Electrical Construction: Primary and Secondary Circuits

Primary circuit current path

In a fixed ABB Emax 2 breaker, the current path is: line busbar → bolted lug → upper terminal → moving contact → arc contact → fixed contact → lower terminal → bolted lug → load busbar. Two bolted joints in total per pole.

In a withdrawable breaker, the path adds two cluster-contact interfaces per pole — line and load. Each cluster has 12–24 silver-plated fingers, depending on frame, in parallel. Contact resistance per cluster is specified by ABB at less than 8 µΩ at 20 °C. So the withdrawable version dissipates marginally more heat at full load.

For an E2.2B 2000 such as the ABB 1SDA071021R1 E2.2B 2000 Ekip Dip LI, that works out to approximately 192 W of extra dissipation in the cassette at rated current. Not huge in absolute terms, but it shifts the cabinet thermal calculation. The IEC 60890 hot-spot calculation for the panel must include this. Skip it and you risk derating the breaker by 5–10 % when the ambient inside the cubicle climbs above 50 °C.

Secondary circuit (control wiring)

This is where withdrawable construction earns most of its complexity. Auxiliary contacts, motor-operator supply, undervoltage release, shunt trip, Ekip communication module — all of these must disconnect automatically when the breaker is racked out, otherwise you cannot lift it from the cradle.

ABB uses a sliding multi-pin connector on the top of the cassette, rated for at least 1000 operations. The pin assignment is fixed by ABB's wiring scheme (see manual 1SDH001000R1002). A common mistake during commissioning is to land a third-party communication cable directly on the breaker terminal instead of routing it through the cassette plug — the moment someone racks out for testing, the cable is torn off.

Operational and Maintenance Differences

Three positions versus one

The withdrawable ABB Emax 2 breaker offers three defined positions per IEC 60947-2 §7.1.7:

Connected: primary and secondary contacts engaged. Normal operation.

Test: primary contacts open and visibly isolated, secondary contacts still engaged. You can exercise the trip unit, motor-charge the springs, run open/close cycles, verify shunt trip and undervoltage operation, all without energizing the load. This position is invaluable during planned outages and SAT (Site Acceptance Testing).

Isolated: both primary and secondary disconnected. Shutters close automatically. The breaker can be removed entirely.

Fixed breakers have one position: bolted in place. Testing requires either upstream isolation or temporary disconnection of the trip circuit — both of which introduce procedural risk.

Mean time to repair (MTTR)

In a 2022 reliability study of a Middle East refinery's 6.6 kV/400 V LV system, the maintenance contractor logged MTTR figures across 38 ACBs. Withdrawable units averaged 47 minutes per replacement. Fixed units averaged 4 hours 12 minutes — and that excluded the upstream LOTO time, because upstream isolation was already required for the rest of the planned shutdown.

If your facility runs continuous process — refining, semiconductor fabs, food-and-beverage CIP cycles, hyperscale data centers — withdrawable is rarely a question of cost. It is a question of whether you can take a 4-hour outage on a feeder.

Standards, Testing and Compliance

Both versions of the ABB Emax 2 are tested and certified to IEC 60947-2. The same Icu/Ics/Icw figures apply. The differences appear in two specific places:

First, IEC 60947-2 §7.2.7 requires that withdrawable breakers in the isolated position satisfy the isolation requirements of IEC 60947-3, including impulse withstand voltage (Uimp) of 12 kV across the open contacts and a verified clearance/creepage distance. ABB publishes these test reports per cassette type.

Second, IEEE C37.13 and ANSI/NEMA SG-3 — used in North American specifications — define drawout breakers explicitly and require a positive mechanical interlock against racking under load. The Emax 2 cassette meets this. Engineers writing specs for global projects should call out both standards: "withdrawable execution per IEC 60947-2 and IEEE C37.13 §6.4." That language preempts vendor disputes.

Short-circuit performance

People sometimes assume that the cluster contacts are the weak point under fault current. In practice, the magnetic forces during a short-circuit pull cluster fingers tighter against the male contact (a designed-in feature called the "Holm effect" leveraged by ABB). The breakdown limit is the fixed-bolted lug on the busbar side, not the cluster. Both versions of the E2.2B carry the same 42 kA Icu at 440 V — verified by type test on the cassette assembly, not just the breaker module.

Cost Comparison: Capex vs Lifecycle

Where fixed wins

In our experience, the fixed ABB Emax 2 wins clearly in three scenarios. First, secondary distribution boards downstream of an MCC where the breaker rarely operates and where local sub-feeders can be isolated quickly. Second, generator output breakers on standby gensets where the breaker is exercised monthly and inspected rather than swapped. Third, captive industrial sites with cold-spare panels — if you can mobilize a complete spare cubicle, the cassette premium loses its justification.

For a 1000 A static load feeding a workshop, the ABB 1SDA070781R1 E1.2B 1000 fixed with LI protection or the LSI variant ABB 1SDA070782R1 E1.2B 1000 LSI is a sound, lower-cost choice.

Where withdrawable wins

Process industries, hospitals, hyperscale data centers, and any facility where IEC 61439-2 form 4b segregation is specified. Form 4b implies cable-form separation between functional units; the cassette construction lines up naturally with that segregation requirement. Substituting fixed breakers into a form 4b panel means custom partitioning — usually more expensive than the cassette premium itself.

Specification Pitfalls and Field Lessons

Mixing fixed and withdrawable in one lineup

Procurement managers under cost pressure often ask: can we use withdrawable ABB Emax 2 on the incomers and fixed on the outgoing feeders? Technically yes, and it is common practice. But beware of three pitfalls.

The first is panel height: a withdrawable cassette aligned next to a fixed unit creates an awkward step in the cubicle door arrangement. Most panel builders solve this by using the cassette dimensions as the standard module height across the lineup, which means your fixed breakers occupy oversized cells.

The second is spare-parts inventory. If your incomer is a withdrawable E4.2 and your feeders are fixed E1.2 and E2.2, you need three spare parts strategies. We recommend standardizing on cassette-compatible breakers across the same frame size at minimum.

The third is racking handle compatibility — ABB uses one handle for E1.2/E2.2 and a different one for E4.2/E6.2. In a hurry, operators have stripped the racking screw using the wrong handle. Label the handles. Mount them on the panel door.

Ekip trip unit settings travel with the breaker

This is a quiet advantage of withdrawable construction. Ekip Dip, Ekip Touch, and Ekip Hi-Touch trip units are mounted on the breaker module, not on the cassette. When you swap a withdrawable Emax 2, the new unit needs to be re-programmed unless you save settings via the Ekip Connect software and restore them. Some commissioning teams keep a USB stick taped inside the panel door with the saved profile for each breaker. Cheap, effective, and far better than scrolling through menus during an emergency at 2 a.m.

For the deeper procedure see the Emax 2 full technical specifications guide, which lists Ekip variant compatibility per frame.

The selectivity question

Fixed and withdrawable construction does not change selectivity behavior. Coordination tables published by ABB (1SDC200023D0207 and similar) are valid for both. What can change is your willingness to set instantaneous (I) protection close to the lower limit on a feeder breaker — because if it nuisance trips, a fixed breaker is harder to reset and inspect than a withdrawable one. Engineers sometimes set I conservatively on fixed breakers to avoid reset trips, sacrificing arc-flash energy reduction. The cassette gives you the option to be more aggressive with settings, knowing maintenance access is straightforward.

Choosing Between Versions: A Decision Framework

Step 1 — Criticality of the circuit

Ask: if this ABB Emax 2 breaker fails, what is the consequence? If it is loss of a critical process, redundant cooling chiller, hospital surgical wing, or telecom core, withdrawable is the default. For a non-critical lighting subdistribution? Fixed is fine.

Step 2 — Outage tolerance

Ask: how long can the upstream main be off to replace this breaker? If "less than an hour," you need withdrawable. If "we have a planned weekend shutdown twice a year," fixed is acceptable.

Step 3 — Form of separation

Ask: does the panel specification require IEC 61439-2 Form 3b or 4b? Withdrawable breakers integrate more neatly with these forms. Most form 4 panels in process industries default to withdrawable for this reason alone.

Step 4 — Total cost of ownership over 25 years

Run a simple TCO model. Take the capex delta (typically €1,500–€4,000 per breaker for the cassette premium), add the present value of two unplanned outages over 25 years at your facility's downtime cost per hour, and compare. For continuous-process plants the TCO favors withdrawable in nearly every case. For light commercial or non-critical industrial, fixed wins. There is no universal answer because it depends on duty cycle, redundancy architecture, and the cost of an unplanned hour of downtime.

For a structured sizing approach that feeds into this decision, see our step-by-step Emax 2 sizing calculator. And if you are weighing ABB against the equivalent Schneider offer, the Emax 2 vs MasterPact MTZ comparison covers cassette interchangeability and racking compatibility — the two are not mechanically interchangeable, despite similar electrical specs.

Real-World Examples from Industrial Facilities

Cement plant, North Africa, 2021

A 5500 t/day cement line in Algeria specified all 12 LV incomers as fixed ABB Emax 2 breakers to save approximately €38,000 across the project. Two years later, an arc fault on a kiln drive feeder destroyed an E2.2B 1600. Replacement required isolating the entire 1600 kVA transformer feeding the section, a 9-hour outage, and lost production worth approximately €420,000. The site has since retrofitted withdrawable cassettes on all critical feeders. The lesson is uncomfortable but consistent: capex savings on construction type are usually a false economy on critical feeders.

Tier III data center, Frankfurt, 2023

A 30 MW colocation facility specified withdrawable E4.2 incomers and withdrawable E2.2 generator-coupling breakers, but used fixed E1.2 versions like the ABB 1SDA070741R1 E1.2B 800 for non-critical mechanical loads (lighting, BMS power, cleaning sockets). Mixed-construction approach, justified by criticality. Total cassette premium versus all-withdrawable: approximately €52,000. Reasonable engineering.

Pharmaceutical plant, Ireland

An MHRA-validated facility specified all withdrawable Emax 2, including downstream feeders to non-critical loads. Why? Because the validated cleaning protocols meant that any panel intervention required a re-validation event. Withdrawable cassettes allowed breaker maintenance without opening the validated enclosure beyond the breaker cell. The premium paid for itself within the first maintenance cycle in avoided revalidation cost.

Practical Specification Language

When writing tender documents, vague language costs money. Procurement teams routinely receive bids interpreting "ABB Emax 2 type" loosely. Here is precise language that we have seen close ambiguity:

"Main incoming circuit breakers shall be ABB SACE Emax 2, frame [E2.2/E4.2 as applicable], withdrawable execution per IEC 60947-2 §3.1.4 with isolation function per IEC 60947-3, three positions (connected/test/isolated), automatic safety shutters, mechanical and electrical interlocks against racking under load, motor-operated spring charging, and Ekip Touch LSIG trip unit. Outgoing feeder breakers below 1000 A may be fixed execution where permitted by the criticality assessment."

That paragraph eliminates a half-day of clarification e-mails. For background on what "Emax 2" actually encompasses, the foundational overview of the Emax 2 family is a useful tender attachment for procurement managers who are not breaker specialists.

Inventory and Spares Strategy

One subtle benefit of withdrawable construction is that you can stock fewer spares. A single E2.2B 2000 module spare can cover any of N withdrawable cassettes of the same frame and rating across the facility. Fixed breakers are bolted into specific busbar geometries — sometimes the same SKU, sometimes with different terminal orientations (front, rear, vertical) that prevent direct substitution.

For sites with multiple Emax 2 frames in service, our usual recommendation is one spare module per frame size in withdrawable execution, kept in climate-controlled storage with the trip unit pre-programmed to a "default safe" profile that can be over-written on installation. We also recommend stocking a complete spare cassette per frame, in case the cassette itself is damaged by a fault — rare, but not unheard of in 65 kA-rated installations.

For ancillary protection components — feeder MCCBs, downstream MCBs, RCDs — see the broader catalog at Stoklink including air circuit breakers, miniature circuit breakers, residual current devices, and protection relays.

Common Misconceptions

"Withdrawable means more failure points"

Statistically, no. ABB's reliability data on Emax 2 (publication 1SDC200016D0202) shows MTBF figures within 5 % between fixed and withdrawable across a population of 18,000 units in service. The cassette adds components but does not introduce statistically significant failure modes when racking discipline is observed.

"Fixed has lower contact resistance, so it runs cooler"

True at the joint level, false at the system level. Cluster contacts run slightly warmer, but a fixed breaker that suffers a loose terminal (the most common fixed-version failure mode) generates far more heat than any cassette. Properly maintained, the temperature difference is negligible — about 5–8 K at full rated current.

"Withdrawable is overkill below 1000 A"

Often true for non-critical loads. But for generator coupling at any current rating, withdrawable is justified by the test position alone — the ability to exercise the breaker monthly during genset tests without de-energizing the bus is operationally invaluable.

Related Reading

• 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
• ABB Emax 2 Nuisance Tripping: Root Causes, Diagnostic Steps and Fixes

Conclusion

The choice between withdrawable and fixed Emax 2 is not a checkbox — it is a deliberate engineering decision that ripples through capex, operational availability, maintenance procedures, panel design, and spare parts strategy for the entire 25-year asset life. Fixed versions like the ABB 1SDA070821R1 E1.2B 1250 fixed or the ABB 1SDA070981R1 E2.2B 1600 fixed are the right answer for many secondary distribution and non-critical applications, where their lower cost and compact footprint genuinely benefit the project. Withdrawable construction, with its three-position cassette, automatic shutters, and 20-minute MTTR, is the right answer wherever continuous availability is the dominant constraint — process industries, data centers, healthcare, and any facility where an unplanned 4-hour outage costs more than the cassette premium.

Specify based on criticality, not on price alone. Use the same frame across at least one execution type for spare-parts efficiency. Always cite IEC 60947-2 and, for North American projects, IEEE C37.13 in the tender documents. And remember that the breaker module itself is identical between versions — what you are really buying with the cassette is operational flexibility and the ability to test, maintain, and replace without taking the upstream main offline. For the complete selection methodology, application notes, and maintenance schedules, refer to the ABB SACE Emax 2 selection, application and maintenance guide, which ties this construction decision into the wider engineering workflow for low-voltage power distribution.