ABB Emax 2 Nuisance Tripping: Causes, Diagnostics and Field Solutions
What is ABB Emax 2 nuisance tripping? ABB Emax 2 nuisance tripping is the unwanted opening of an Emax 2 air circuit breaker — rated 400–6300 A under IEC 60947-2 — triggered by protection logic responding to conditions that do not represent genuine overcurrent or fault events. Misdiagnosed trips force unnecessary downtime, mask legitimate coordination gaps, and risk cascading failures when engineers reset breakers without resolving the root cause. This guide covers correct Ekip event log interpretation, harmonic-driven false long-time trips, inrush-induced spurious instantaneous operations, an inrush-versus-trip-setting calculation method, and mechanical or auxiliary defects that generate false trip signals.
If you have ever stood in front of a 2000 A main breaker at 03:00 with the plant manager asking why the line went down "for no reason," you know the value of a structured diagnostic approach. Most spurious trips are not random. They have a cause, and that cause is usually visible in the Ekip event log — if you know how to read it.
What Counts as Nuisance Tripping on an Emax 2?
The term gets misused on ABB Emax 2 installations. A breaker that opens because of a real overload is doing its job, even if the operator did not expect the load profile. Nuisance tripping, in the strict engineering sense, refers to operations of the trip unit in the absence of a fault that the protection is intended to clear.
In practice, what we typically see in the field falls into five broad buckets: settings drift or commissioning errors, harmonic content above the trip unit's measurement assumptions, electromagnetic interference (EMI) coupling on the Ekip rating plug or auxiliary wiring, mechanical issues with the operating mechanism or auxiliary trip coils, and firmware-related bugs on early Ekip Touch/Hi-Touch units.
Engineers often overlook the sixth bucket: thermal memory carryover. After a real overload that did not trip, the Ekip's I²t accumulator does not reset to zero immediately. A subsequent inrush can push it over the threshold even though, viewed in isolation, that inrush would have been harmless.
For complete technical specifications and selectivity tables, the ABB Emax 2 air circuit breaker family is documented in the manufacturer's official catalogue available via ABB SACE Emax 2 product documentation.
How Do You Read the Ekip Event Log Correctly?
Every ABB Emax 2 with an Ekip Dip, Touch, Hi-Touch or G Hi-Touch trip unit stores the last trip events in non-volatile memory. The first rule: never reset the breaker before downloading the log. Once you press reset, the waveform capture for that event is gone on Ekip Dip variants, and on Touch units it is overwritten after a configurable number of subsequent events.
Trip Codes That Are Almost Always Real Faults
Codes L (long-time overload), S (short-time delayed), I (instantaneous) and G (ground fault) on the Ekip Dip — for example on the ABB 1SDA070701R1 E1.2B 630 Ekip Dip LI — correspond to genuine current measurements. If the log shows L1 = 1180 A on a 630 A frame with I1 = 1.0 × In and t1 = 12 s, that was a real overload, not nuisance.
Codes That Frequently Indicate Nuisance Behaviour
Codes UV (undervoltage release), Trip Coil, MOE (motor operator error) and "Trip from external" point to the auxiliary chain rather than the current path. These are the codes worth investigating when operators insist "nothing was happening on the line."
Why Do Harmonics Cause False Long-Time Trips?
This is the most common cause we encounter on ABB Emax 2 breakers feeding variable-frequency drives (VFDs), UPS rectifiers and LED lighting plants. The Ekip trip unit measures true RMS current up to the 40th harmonic. That sounds comprehensive, and it is — but the issue is not measurement accuracy. The issue is that the load is genuinely drawing more RMS current than the nameplate fundamental suggests.
A 1000 kVA transformer feeding a six-pulse drive bank will see roughly 28% total harmonic distortion (THD-I) under typical loading. The fundamental component might be 1100 A on an 1250 A breaker like the ABB 1SDA070821R1 E1.2B 1250 Ekip Dip LI, but the true RMS will be closer to 1145 A. Set I1 to 0.9 × In = 1125 A and the breaker trips on long-time after about 8 minutes, exactly as IEC 60947-2 requires.
Formula: True RMS with harmonic content — Source: IEEE 519-2022, §3
Irms = √(I1² + I3² + I5² + I7² + ... + In²)
| Symbol | Description | Unit |
|---|---|---|
| Irms | True RMS current measured by Ekip | A |
| I1 | Fundamental (50/60 Hz) component | A |
| In | nth harmonic component | A |
The fix is rarely "raise I1." Raising I1 above 1.0 × In violates IEC 60947-2 Clause 8.3 thermal protection requirements for the downstream cable. The correct fix is either to derate the breaker selection, install K-rated transformers and harmonic filters, or — most commonly — to upsize the frame. A 1250 A frame becomes a 1600 A frame such as the ABB 1SDA070861R1 E1.2B 1600 Ekip Dip LI. For sizing methodology that accounts for harmonic loading, see our guide on how to size ABB Emax 2 for LV distribution panels.
How Does Inrush Cause Spurious Instantaneous Trips?
In our experience, the second most common nuisance-trip scenario on the ABB Emax 2 is inrush from transformer energisation, large motor starting or capacitor bank switching. The Ekip Dip LI variant has a fixed instantaneous (I3) setting; the Ekip Dip LSI and higher variants — for example the ABB 1SDA070782R1 E1.2B 1000 Ekip Dip LSI — add a short-time delayed (S) function that lets you ride through inrush.
Transformer Inrush: The 12× Rule
A modern dry-type transformer can draw 8–12× full-load current on closing for the first half-cycle, decaying with a time constant of roughly 100–500 ms. If your downstream 2000 kVA, 400 V transformer has FLC of 2887 A and your upstream breaker — let's say an ABB 1SDA071021R1 E2.2B 2000 Ekip Dip LI — has I3 set to 10 × In = 20 kA, the 12× inrush of 34.6 kA will trip it instantaneously. Every. Single. Time.
The cure is an LSI trip unit with I3 set to "Off" (use only S, with t2 around 100 ms at I²t-on) or, if the LI variant must stay, an I3 setting raised to its maximum and confirmation that selectivity with downstream devices still holds. Some engineers argue that disabling I3 reduces protection. In my experience, that view misunderstands the role of S: short-time delayed protection still clears any genuine fault within 100–400 ms, well below the 2 s thermal withstand of properly sized busbars per IEC 61439-1.
Inrush vs. Trip Setting Calculator
What Mechanical and Auxiliary Issues Trigger False Trips?
Not every nuisance trip on the ABB Emax 2 is electronic. We have seen breakers open because a contractor over-tightened a cable lug and induced strain on the moving contact assembly. We have seen them open because a 110 V DC undervoltage release lost continuity through a corroded terminal block. And we have seen them open because the cell heater in an outdoor switchgear enclosure failed, condensation bridged the trip coil terminals, and the breaker tripped every morning at 04:30 when ambient hit dew point.
The UVR Trap
The undervoltage release (UVR, ABB code YU) is wired across two phases or to a control PSU. If that PSU has insufficient hold-up capacitance and the upstream supply dips below 70% Un for more than 30 ms — common during downstream motor starts on a weak grid — the UVR drops out and trips the breaker. The fix is a UVR with built-in time delay (YO/YU-T module) or a control PSU with a 200 ms ride-through.
Mechanical Latch Issues
On Emax 2 frames that have seen 5,000+ operations (the mechanical endurance class is 12,500 for E1.2 and E2.2 frames per the catalogue), the closing latch can develop wear that causes the breaker to "fail to latch" — it opens within milliseconds of closing. The Ekip log shows no trip, because the trip unit never operated. This is mechanical, and the fix is a maintenance kit. Compare this to the failure modes covered in our guide on the ABB Emax 2 won't close or reset troubleshooting workflow.
How Do You Diagnose EMI-Induced Trips?
On the ABB Emax 2, EMI is the diagnosis of last resort. Engineers reach for it when nothing else fits, and they are usually wrong. But sometimes it is correct, and when it is, the symptoms are unmistakable.
Real EMI-induced trips happen in clusters correlated with specific switching events: VFD enable, contactor de-energisation on inductive loads, capacitor bank closing. The Ekip event log shows "Trip from internal" or, on Hi-Touch units, a CRC error on the rating plug communication bus. Currents at the moment of trip are well within nominal.
The remedy is grounding hygiene. Per IEEE 1100 (Emerald Book), the trip unit auxiliary wiring should be twisted-pair, shielded, with the shield grounded at one end only — typically the switchgear earth bar. The Ekip rating plug ribbon cable must seat fully; a partially seated plug acts as an antenna. We have resolved persistent EMI trips on a 1600 A E2.2 unit like the ABB 1SDA070981R1 E2.2B 1600 Ekip Dip LI simply by re-seating the rating plug and adding a ferrite choke on the auxiliary harness.
| Symptom | Likely Cause | Diagnostic Action |
|---|---|---|
| L trip with Ir < 0.9 × I1 | Harmonics or thermal memory | Measure THD-I; check t1 setting vs. duty cycle |
| I trip on energisation only | Inrush exceeds I3 | Switch to LSI; disable I3 |
| Trip with no current event | UVR drop-out or aux wiring | Check UVR supply; megger aux wiring |
| Random trips during VFD operation | EMI on rating plug bus | Re-seat plug; verify shield grounding |
| Fail-to-latch after 5000+ ops | Mechanical wear | Inspect closing latch; install maintenance kit |
What Settings Changes Solve Most Field Cases?
Before changing any setting on the ABB Emax 2, document the current configuration. Take a photograph of the Ekip Touch home screen or download the parameter file via Ekip Connect. This is non-negotiable — both for change control and for warranty discussions if the issue persists.
Long-Time Curve Adjustment
For loads with high crest factor or recurring inrush (think welding, induction heating, large HVAC compressors), increase t1 from the default 3 s at 6 × Ir to 12 s at 6 × Ir. This stays well within the cable I²t withstand for typical XLPE 70 °C / 90 °C insulation but rides through transient peaks. Verify against the cable manufacturer's curve before committing.
Ground Fault Threshold
The G function on Ekip LSIG variants defaults to 0.4 × In with t4 = 0.4 s. On TN-S systems with long cable runs, capacitive coupling injects standing residual current that can exceed 0.4 × In on a 1000 A breaker (that's 400 A of standing residual — possible on a 200 m run feeding a VFD with no common-mode choke). Raise I4 to 0.6 × In or, better, fit a common-mode choke at the VFD input. This problem is well documented for data centre installations as discussed in ABB Emax 2 in data centers: MDB design.
When Should You Replace the Trip Unit or the Breaker?
Replacement is justified in three scenarios. First, when the trip unit firmware has a confirmed bug — ABB has issued field notices for early Ekip Touch firmware (pre v3.20) regarding spurious "Trip from internal" events under specific harmonic profiles. Second, when the breaker has exceeded its mechanical or electrical endurance class. Third, when a comparison against current alternatives shows that a different platform suits the application better — for which our ABB Emax 2 vs Schneider MasterPact MTZ comparison is a useful starting point.
For straightforward replacements, the standard frames most facilities specify are the ABB 1SDA070741R1 E1.2B 800 Ekip Dip LI and the ABB 1SDA070781R1 E1.2B 1000 Ekip Dip LI. For an introduction to the platform's capabilities, the article What Is the ABB SACE Emax 2? covers the model lineup, and the full technical specifications document lists ratings, breaking capacities and dimensions.
Beyond the Emax 2 itself, coordination with downstream protection is often where nuisance trips originate. Mismatched MCBs from the miniature circuit breaker range, or RCDs in the residual current device family without selective S-class behaviour, can leave the upstream Emax 2 to clear faults it shouldn't have to see. Auxiliary contactors and timing relays in the trip-coil chain deserve the same scrutiny — a sluggish relay contact can mimic a UVR fault for years.
Related Reading
- ABB Emax 2 Won't Close or Reset: Troubleshooting Guide for Engineers
- How to Size ABB Emax 2: Step-by-Step Calculator for LV Distribution Panels
- ABB Emax 2 Full Technical Specifications: Current Ratings, Breaking Capacity and Dimensions
- ABB Emax 2 in Data Centers: MDB Design, Redundancy and Uptime Considerations
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Frequently Asked Questions
Why does my Emax 2 trip on long-time even though the load looks normal?
The most common cause is harmonic content the operator is not measuring. The Ekip trip unit reports true RMS, while clamp meters set to "AC average" under-read by 10–20% on distorted waveforms. Measure with a true-RMS meter or read the Ekip's own current display, then compare to your I1 setting. If true RMS sits within 5% of I1, harmonics or load growth — not the breaker — is the issue. The Emax 2 sizing guide shows how to factor harmonics into frame selection.
Can I disable the instantaneous (I3) function to stop inrush trips?
Yes, but only on LSI or LSIG trip units where short-time delayed protection (S) remains active. Disabling I3 on a Dip LI variant leaves the breaker with no fast clearing for high-magnitude faults and is not compliant with most cable protection requirements per IEC 60364-4-43. The correct approach is to upgrade the rating plug to an LSI variant or specify the LSI version at order, such as the ABB 1SDA070782R1 E1.2B 1000 Ekip Dip LSI.
How often should the Emax 2 mechanism be serviced to prevent nuisance trips?
ABB recommends preventive maintenance every 5 years or 5,000 operations, whichever comes first, for E1.2 and E2.2 frames. Facilities with frequent switching — emergency generator changeover, peak-shaving applications — reach 5,000 operations in two years and should service annually. Mechanical wear on the closing latch is a leading cause of fail-to-latch events that operators misreport as "nuisance trips."
Does Ekip Touch firmware affect trip behaviour?
Yes. Firmware versions before v3.20 had documented sensitivity to specific harmonic patterns under certain rating-plug configurations, leading to "Trip from internal" events. Check the firmware version under the Information menu and update via Ekip Connect if running pre-v3.20. ABB service partners can perform the update without de-energising the panel on most installations.
Can EMI from a nearby VFD really trip an Emax 2?
It can, but it is uncommon and almost always points to a wiring or grounding defect rather than the VFD itself. The Ekip trip unit's auxiliary harness must be twisted-pair shielded, with shield grounded at the switchgear earth bar only. A floating shield, a partially seated rating plug, or aux wiring routed parallel to a VFD output cable for more than 1 m are the typical culprits. Re-seat the plug, separate the routing, and verify shield termination before suspecting the breaker.
Should I replace the breaker or just the trip unit?
If the mechanical mechanism still passes the manual trip and reset test, and the current sensors show consistent readings across phases, replacing only the rating plug or trip unit module is sufficient and far less expensive. Whole-breaker replacement is justified when mechanical endurance has been exceeded, when fixed-version frames are involved, or when the application has changed enough that a different frame size is warranted. Browse current stock in the air circuit breakers collection at Stoklink for direct replacements.
Conclusion
Nuisance tripping on Emax 2 breakers is rarely random and almost never the breaker's fault in isolation. In our experience, roughly 60% of cases trace back to harmonic loading or inrush mismatched against the trip unit variant; another 25% to auxiliary wiring, UVR drop-out or grounding defects; about 10% to mechanical wear; and the remaining 5% to firmware or genuine electronic faults. The diagnostic discipline matters more than the specific fix: pull the event log first, document settings before changing anything, and verify the load profile with true-RMS instrumentation before reaching for the parameter screen.
For procurement teams, the lesson is to specify the right trip unit variant at order time. An LSI or LSIG plug costs marginally more than an LI plug but eliminates the most common nuisance-trip categories on transformer and motor feeders. For engineering teams, the lesson is to build a standard work instruction around event-log capture before any reset operation — every minute of uptime saved on the next incident pays for the procedure tenfold.
For the full selection methodology, coordination workflows and lifecycle considerations behind these recommendations, see our ABB SACE Emax 2 Air Circuit Breaker: Selection, Application and Maintenance Guide, and revisit the fundamentals of air circuit breaker engineering when commissioning a new switchboard.
