ABB Emax 2 in Hospital Critical Power Distribution Systems Guide

31 May, 2026
Posted by: Muhammet KUL

What is an ABB Emax 2 hospital critical power distribution system? An ABB Emax 2 hospital critical power distribution system is a low-voltage switchgear architecture built around IEC 60947-2–listed air circuit breakers rated 400–6300 A, engineered to maintain uninterrupted power across normal, essential, and life-safety branches under NFPA 99 and IEC 60364-7-710 requirements. Mismatched frame selection, improperly configured Ekip trip units, or unresolved selectivity gaps during ATS transfer events can collapse discrimination coordination and black out critical surgical or ICU loads. This guide covers LV breaker requirements for healthcare facilities, normal-essential-critical branch architecture, Emax 2 frame-to-load matching, Ekip trip unit parameterization for healthcare loads, selectivity during ATS transitions, and transformer-based frame sizing calculations.

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

Why Hospitals Demand a Different Class of LV Breaker

Hospitals are not factories. A welding shop can absorb a five-second voltage dip; a cardiac catheterization lab cannot. The IEC 60364-7-710 standard for medical locations divides patient areas into Group 0, Group 1, and Group 2, with Group 2 (operating rooms, ICUs, intensive care) requiring an automatic supply changeover within 0.5 seconds for safety services and a maximum 15-second restoration for essential services. NFPA 99 in North America divides loads similarly into Type 1 essential systems with life safety, critical, and equipment branches — and at every transition point, an upstream protective device such as the ABB Emax 2 must clear faults without compromising those time windows.

What does this mean for the breaker at the top of your MDB? It means the device must do four things at once: sense a real fault in milliseconds, ride through generator voltage transients without nuisance tripping, coordinate selectively with downstream MCCBs and MCBs so that a fault in one OR does not black out an entire wing, and report all of the above to a BMS that biomedical engineering will audit during Joint Commission inspections.

Selectivity (discrimination) is defined as the coordinated operation of series-connected protective devices to provide stepped disconnection, ensuring that only the device immediately upstream of the fault opens (per IEC 60947-2 Annex A).

In our experience commissioning hospital switchgear across three continents, the single most common cause of nuisance outages in healthcare LV systems is not equipment failure — it is poor coordination between the incoming ACB and the feeder MCCBs. A fault on a 250 A laundry feeder should never take down the 1600 A incoming breaker. Yet we see it. Often.

For complete technical parameters and type-test certifications of the ABB Emax 2 air circuit breaker family, refer to the manufacturer's official catalogue published by ABB at ABB SACE Emax 2 product documentation.

Architecting the Hospital LV System: Normal, Essential, Critical

A typical mid-sized hospital (300–500 beds) uses a tri-level supply architecture, often anchored at the main incomer by an ABB Emax 2 ACB. The normal source feeds non-critical loads — kitchens, administration, parking. The essential source, fed from the standby generator via an automatic transfer switch (ATS), serves life-safety lighting, fire alarms, and elevators. The critical (or life-safety in NFPA terms) branch handles patient-care equipment with UPS backup feeding into a second-level ATS or static transfer switch.

Where the Emax 2 Fits

At the main incomer position, the Emax 2 frame size is dictated by transformer secondary current. For a 1600 kVA transformer at 400 V, full-load current is approximately 2310 A, which means the ABB 1SDA071021R1 E2.2B 2000 A with HR (high-rated) terminals is undersized — you would step up to an E4.2 frame. For an 800 kVA transformer the calculation gives ~1155 A, so the ABB 1SDA070821R1 E1.2B 1250 A is the natural fit.

Formula: Transformer Full-Load Secondary Current — Source: IEC 60076-1

I_FL = S / (√3 × U_n)

Symbol	Description	Unit
I_FL	Full-load secondary current	A
S	Transformer rated apparent power	VA
U_n	Rated secondary line-to-line voltage	V

Key takeaway: Always size the incoming Emax 2 with a minimum 25% headroom above transformer FLA to accommodate future load growth and to keep the breaker operating below the thermal pickup setpoint during sustained peak demand.

Frame Selection: Matching Emax 2 Models to Hospital Loads

Hospital MDB design is rarely a clean slate. You are usually dealing with a brownfield expansion, an existing transformer pad, and a fixed footprint. The ABB Emax 2 family handles this with four frame sizes (E1.2, E2.2, E4.2, E6.2) sharing common accessories, so you can mix frames in the same switchboard without retraining the maintenance staff.

E1.2 Frame — Feeders and Sub-Distribution

The E1.2 covers 630 A to 1600 A in a compact 324 mm wide frame. For sub-distribution panels feeding ward floors, the ABB 1SDA070701R1 E1.2B 630 A with Ekip Dip LI trip unit is a workhorse. The "B" performance level offers 42 kA Icu at 415 V, sufficient for most hospital secondary distribution where transformer impedance limits prospective short-circuit current.

For the radiology department — CT and MRI machines have aggressive inrush — the ABB 1SDA070741R1 E1.2B 800 A handles the 8–10× inrush profile if the instantaneous setting is correctly biased. Engineers often overlook the fact that an MRI gradient amplifier can pull 600 A peak for 200 ms without being a fault.

E2.2 Frame — Main Incomers

For 1600–2500 A applications such as main incomers on dual-transformer systems, the ABB 1SDA070981R1 E2.2B 1600 A with horizontal rear (HR) terminals integrates cleanly into top-fed switchboards. The HR terminal arrangement matters in hospitals because the rear-access cable management saves on switchgear width — and floor space in hospital electrical rooms is always negotiated against MEP, not given.

Criteria	E1.2B 1000 A	E1.2B 1600 A	E2.2B 1600 A
SKU	1SDA070781R1	1SDA070861R1	1SDA070981R1
Icu @ 415 V	42 kA	42 kA	42 kA
Icw (1 s)	42 kA	42 kA	66 kA
Frame width	324 mm	324 mm	404 mm
Best fit	Sub-MDB feeders	Sub-MDB main	Main incomer
Trip unit	Ekip Dip LI	Ekip Dip LI	Ekip Dip LI

The Icw (short-time withstand current) difference is the engineering reason to step from E1.2 to E2.2 on incomers: a 66 kA / 1 s rating gives the downstream breakers time to clear without the upstream incomer self-tripping on instantaneous. This is the foundation of zone-selective interlocking. For deeper specs see our Emax 2 full technical specifications reference.

Trip Unit Configuration for Healthcare Loads

The Ekip Dip LI trip unit standard on the breakers above provides Long-time and Instantaneous protection. For most hospital sub-distribution this is enough. But on the main incomer, you almost always want LSI or LSIG — adding Short-time delay and Ground-fault protection — which is precisely why ABB Emax 2 trip units are offered across the full LSIG range. The reason: selectivity windows. With only LI, the incomer will instantaneous-trip on any high-current event, defeating discrimination.

The ABB 1SDA070782R1 E1.2B 1000 A with Ekip Dip LSI is what we typically specify for sub-MDB incomers feeding critical-care branches. The S-function delay band, set to 200–400 ms, lets a downstream MCCB clear a fault in 50–80 ms while the upstream Emax 2 watches and waits.

Setting Recommendations for Hospital Service

L (Long-time): 0.9–1.0 × In for incomers; thermal memory ON to prevent reset abuse
S (Short-time): 4–6 × Ir, time delay 200 ms with I²t OFF for clearer coordination
I (Instantaneous): Set to 8–10 × In on incomer to ride through transformer inrush during ATS retransfer
G (Ground): 0.3–0.5 × In, time delay 200–400 ms — critical for IT-system medical groups per IEC 60364-7-710

Key takeaway: A common mistake is leaving the instantaneous setting at the factory default of 12 × In. During generator-to-mains retransfer, transformer magnetizing inrush can hit 11 × In for two cycles, causing nuisance trips that look mysterious until you pull the Ekip waveform capture.

Selectivity and the ATS Transition Problem

In our experience, the most subtle issue in hospital power design is the interaction between the ABB Emax 2 instantaneous setting and the transfer switch closed-transition behavior. Modern ATSs offer closed-transition (CTTS) modes that briefly parallel the generator with utility — typically 100 ms or less. During that overlap, available short-circuit current can momentarily double.

If your incomer Emax 2 is set with I = 8 × In and the prospective Isc during overlap exceeds that pickup, the breaker will trip — exactly when you need it not to. The mitigation: either coordinate with the ATS supplier to confirm overlap Isc, or use the Emax 2's closed-transition signal input to temporarily raise the instantaneous setting via the Ekip Touch trip unit's adaptive protection logic.

This kind of interaction is why we recommend reading our piece on Emax 2 nuisance tripping root causes before commissioning, and why hospital projects benefit from Ekip Touch over Ekip Dip when budget permits.

Calculator: Emax 2 Frame Sizing for Hospital Transformers

For a worked example: a 2000 kVA transformer at 400 V gives I_FL = 2887 A, with 25% headroom = 3609 A. Round up to 4000 A — that is an E4.2 frame. The full air circuit breaker collection at Stoklink includes E4.2 ratings on request. For sizing methodology, the step-by-step Emax 2 sizing calculator walks through the full procedure.

IT System Earth-Fault Monitoring in Group 2 Locations

Group 2 medical locations (operating theatres, ICUs, intensive care) require an isolated IT (Isolé Terre) supply per IEC 60364-7-710 §710.411.6. The reason is patient safety: in a TN-S system, a first earth fault on a patient-connected device draws fault current through the patient. In an IT system, the first fault is benign — the system continues to operate while an insulation monitoring device (IMD) alarms, with the upstream ABB Emax 2 holding the supply intact until maintenance can intervene.

The Emax 2 does not directly serve the IT-isolated bus (that is fed via a 1:1 medical isolation transformer), but it sits upstream as the feeder to the iso-transformer primary. The setting consideration here is the G-function: ground fault detection on the upstream Emax 2 must not trip on capacitive leakage from the iso-transformer secondary, which can be surprisingly high (50–200 mA per OR). Set the G pickup at 0.5 × In with a 400 ms delay.

IT system (per IEC 60364-1) is defined as a power distribution arrangement where no live conductor is directly connected to earth, and exposed conductive parts are earthed independently — used in medical Group 2 locations to maximize continuity of supply during a first insulation fault.

Communication, Metering, and BMS Integration

Hospital facilities teams need real-time visibility. The Ekip Com modules for the ABB Emax 2 add Modbus RTU, Modbus TCP, Profibus, Profinet, and EtherNet/IP — covering virtually any BMS protocol stack you encounter. In one Middle East tertiary hospital project, we tied 14 Emax 2 breakers via Modbus TCP into a Schneider EcoStruxure BMS without a single protocol gateway. That is rare in heterogeneous fleets and a real benefit when the alternative is layered translation.

For comparison, the equivalent Schneider MasterPact MTZ communication options are functionally similar but use IFE/IFM gateway hardware that adds line items to the BOM.

Key takeaway: Specify the Ekip Com module at the breaker order stage, not as a field retrofit — the firmware handshake between trip unit and com module is much smoother when factory-paired, and you avoid a service call to update Ekip Connect 3 firmware on a live hospital MDB.

Maintenance Strategy for 24/7/365 Operation

Hospitals do not have a maintenance shutdown window. Period. Whatever testing you do, you do it with bypass arrangements or during the lowest-load 03:00 window with full coordination from clinical engineering. The ABB Emax 2 supports this through:

Front-accessible withdrawable racking (no rear access required)
Ekip Connect 3 software for trip unit testing without primary injection
Mechanical interlocking kits for safe ATS bypass operation

For data center cousins of hospital design — also 24/7 critical — see our Emax 2 in data centers MDB design article; many of the redundancy principles cross over.

In practice, what we typically see in the field is that hospitals over-specify breaker mechanical operations life (factory rated 12,500 CO cycles for E1.2B) but under-specify operator training. A breaker rated for 25 years of service will fail in five if maintenance staff rack it in under load because the kirk-key sequence is not posted on the panel door.

Procurement Considerations: Lead Time, Spares, Standardization

Hospital electrical rooms have a 30-year service expectation. The ABB Emax 2 platform launched in 2014 and ABB has committed to long-term parts availability, but procurement managers should still:

Standardize on one or two frame sizes across the campus to minimize spare-trip-unit inventory
Specify identical accessories (UVR, shunt trip, motor operator) site-wide
Order at least one spare cassette (moving part) per frame size on site
Document the Ekip parameter set as a backup file via Ekip Connect

For background on the platform itself, our overview What is the ABB SACE Emax 2? covers features and model breakdown.

Ready to Source Air Circuit Breakers?

Browse in-stock air circuit breakers
Request a custom quote — response within 4 hours
Talk to an engineer

Frequently Asked Questions

Can the Emax 2 be used as the main breaker on the essential branch downstream of the ATS?

Yes, and it is common practice. The breaker downstream of the ATS sees the same fault current envelope as the main incomer during normal operation but a reduced envelope during generator operation. Size it for the worst case — utility — and verify generator contribution does not undercut the instantaneous pickup, which would defeat selectivity during outage events.

What Icu rating do I need for a hospital MDB on a 1600 kVA transformer?

For a 1600 kVA, 415 V transformer with 6% impedance, prospective short-circuit current at the secondary terminals is approximately 38.5 kA. The 42 kA Icu of the Emax 2 "B" performance level provides adequate margin. For paralleled transformer arrangements (2 × 1600 kVA bus-tied), recalculate with both transformers contributing — you may need the "N" or "S" performance level at 50–66 kA Icu.

Is the Ekip Dip trip unit sufficient, or do I need Ekip Touch for hospital service?

Ekip Dip LSI works for most hospital sub-distribution and even main incomers if you only need protection plus basic communication. Ekip Touch becomes worthwhile when you need adaptive protection (different settings for utility vs generator source), advanced power quality metering, or local color-display diagnostics for clinical engineering staff. Our technical specifications guide compares trip unit feature sets in detail.

How does the Emax 2 handle the 0.5-second changeover requirement of IEC 60364-7-710?

The Emax 2 itself does not perform the changeover — that is the role of the ATS. However, the breaker's role is to not trip during the brief overlap or the inrush that follows. With proper L-S-I-G coordination and an instantaneous setting biased for transformer inrush, the Emax 2 stays closed through the transient. The 0.5 s requirement applies end-to-end to the supply system, not the breaker alone.

Can I use the Emax 2 with a residual current device for additional earth-fault protection?

The Emax 2 can be supplied with an integrated residual-current module (Ekip RC) for the main breaker, but in hospital applications RCDs are typically applied at the final circuit level (30 mA for socket outlets in patient areas per local codes). The upstream Emax 2 G-function provides ground-fault protection, not personal protection. For socket-level RCDs, see the residual current device collection at Stoklink.

What is the typical lead time for an Emax 2 with Ekip Hi-Touch and communication modules?

Standard catalog configurations like the 1SDA070861R1 E1.2B 1600 A are commonly available from stock at 1–2 weeks via European distribution. Configured-to-order versions with Ekip Touch, specific communication modules, or non-standard accessories typically take 6–10 weeks from ABB factory. For hospital projects, plan accordingly and stock at least one common spare frame on site.

How do I verify selectivity between the Emax 2 incomer and downstream MCCBs?

Use ABB DOC software (free) to import the Emax 2 trip curve and the downstream MCCB curves on a single time-current plot. Verify the curves do not cross within the prospective fault current range at the downstream busbar. For coordination beyond Icu of the downstream device, ABB publishes selectivity tables in the technical catalog — these are pre-tested combinations that guarantee discrimination up to specified currents. The same approach works for MCB-level coordination at Stoklink on lighting and small-power feeders.

Conclusion

Hospital critical power distribution is unforgiving territory. The breaker at the top of the MDB has to keep an OR running through a generator transfer, hold its position during transformer inrush, discriminate selectively against a fault on a 32 A ward feeder, and report all of it to a BMS that biomedical engineering audits monthly. The ABB SACE Emax 2 family, properly specified and configured, does this work reliably across the frame range from E1.2 (630 A) to E6.2 (6300 A).

The decisions that matter most are not the obvious ones. Frame size follows transformer kVA and is largely formulaic. The judgment calls are in the trip unit setpoints, the coordination strategy with the ATS, the choice between Ekip Dip and Ekip Touch for adaptive protection, and the long-term standardization across a 30-year hospital lifecycle. Get those right and your hospital LV system will outlast the building services contract that delivered it. Get them wrong and you will be debugging nuisance trips at 03:00 while a clinical lead asks why an OR went dark during a routine generator test.

For procurement managers comparing Emax 2 against alternatives, our Emax 2 vs Schneider MasterPact MTZ comparison covers technical and commercial trade-offs. For the full selection methodology, lifecycle considerations, and maintenance strategy, see the ABB SACE Emax 2: Selection, Application and Maintenance Guide. And when you are ready to specify, the air circuit breaker collection at Stoklink lists current stock with full datasheets and lead times — including the E1.2B 1000 A and E2.2B 1600 A HR models most commonly deployed in healthcare LV systems globally.