Guide · ABB SACE Emax E1–E6
Emax PR121 / PR122 / PR123 trip unit faults and testing
The PR12x trip units on first-generation Emax breakers are out of production, and many are now well over a decade old. Here is how the common faults show up, what ABB's test units can and cannot tell you, and how a full test is recorded.
The three PR12x units in brief
First-generation ABB SACE Emax breakers (E1 to E6) were built from the late 1990s to the early 2010s. The later ones carry PR12x protection releases, which replaced the earlier PR111, PR112 and PR113:
- PR121/P is the basic unit. Protection thresholds and times are set with DIP switches on its front, and alarms are signaled by LEDs.
- PR122/P adds a graphic display with menus, measurement, a trip history and optional internal modules: PR120/V for voltage measurement and power, PR120/K for signaling contacts, PR120/D-M for communication.
- PR123/P adds the more advanced functions, such as dual settings and extra protections, on the same platform.
All three are out of production. When one fails, ABB's usual answer is an Emax 2 retrofit rather than a replacement PR unit.
Common symptoms and what they usually mean
No display, or a blank screen
Check the power supply first. A PR122/P or PR123/P is self-powered from the breaker's current sensors, but only above a minimum three-phase current. ABB's manual puts the switch-on threshold at about 100 A of busbar current on E1–E3 (200 A on E4 and E6), with more needed for full operation and display backlighting. On a lightly loaded or open breaker, a blank display is normal unless a 24 V DC auxiliary supply, a PR120/V module or a PR030/B battery unit is powering the relay.
If the unit stays dead with auxiliary power present, the fault is in the relay itself: a power supply or board failure.
Alarm messages
The PR122/P and PR123/P report alarms on the display; PR121/P uses its LEDs. The ones that point to hardware are:
- TC disconnected: the trip coil is disconnected or faulty. The relay cannot open the breaker until this is fixed.
- Sensor L1 / L2 / L3 / Ne: a current sensor is disconnected or faulty. Look at the sensor, its wiring and the connector before replacing the relay.
- Rating plug: the plug is missing, loose, faulty or the wrong size for the breaker.
- Contact wear: a pre-alarm above 80% of the relay's calculated contact wear, and an alarm at 100%. The contacts need inspection.
- Configuration or Installation: settings or installation data that do not match, often after a relay has been swapped between breakers.
Nuisance tripping
Read the trip history first. It records which element tripped and the current at the time. A genuine overload or ground fault is a system problem, not a relay problem. Ground-fault trips that start after work on the board often come from neutral-sensor or configuration settings. Trips that the recorded currents cannot explain point to drifting electronics, a faulty current sensor or a wiring fault, and that is where a secondary injection test settles it.
Failure to trip in test
If a test shows the relay sending a trip but the breaker does not open, the fault is in the trip path: the trip coil, its wiring or the mechanism itself. Hardened grease or a worn latch can stop a breaker opening cleanly. If the relay does not send a trip at all, the relay or its current sensing has failed.
What ABB's test units can check
ABB makes portable test and configuration units for these relays. They connect to the test connector on the front of the trip unit:
- PR010/T is a stand-alone test unit. It powers the relay and runs an automatic test, a manual test and a trip test. In manual test you choose the simulated current (from 0 to 16 times In) and the phases, and the unit records the trip time and a pass or fail. Test reports can be saved and downloaded to a PC.
- Ekip T&P connects the relay to a PC by USB, for power, communication and testing through ABB's Ekip Connect software.
The PR122/P and PR123/P also have a built-in test menu. Autotest checks the display and LEDs. Trip test sends an opening command to the trip coil; it needs the breaker closed with no current flowing.
These are secondary injection tests. They feed signals into the trip unit instead of the current sensors, and they prove its pickup levels and time delays against the published curve. They are fast and repeatable and need no heavy current. What they do not prove is the current sensors themselves or the wiring between sensor and relay.
Primary injection drives real current through the breaker's poles, proving the whole chain: current sensors, wiring, trip unit and mechanism together. It needs a high-current test set and access to the primary terminals.
ABB's manual warns that dielectric (hipot) tests must not be applied to the inputs and outputs of the PR122/P and PR123/P. Disconnect or isolate the relay before insulation testing the breaker.
What a full test record looks like
Here is a real, anonymized example: an ABB SACE Emax E3N-A 20 (2000 A, 3-pole, fixed), a UL-listed power circuit breaker built to ANSI C37.13, with a PR122/P LSI trip unit and a 2000 A rating plug. Settings: I1 1.0, t1 3 s; I2 1.2, t2 0.1 s with I²t on; I3 1.6.
It arrived with a broken charging handle, a missing CLOSE button and corrosion throughout. The mechanism was fully dismantled, cleaned and rebuilt, and the closing, shunt and undervoltage coils were replaced. The PR122/P was then secondary-injection tested with ABB's Ekip SIM secondary injection test kit:
| Element and test point | Results | Band |
|---|---|---|
| L at 1.5 × I1 | 11.42 / 12.28 / 13.17 s | 10.8–13.2 s |
| L at 3 × I1 | 2.821 / 3.124 / 3.097 s | 2.7–3.3 s |
| S at 2 × I2 | 1.658 / 1.777 / 1.673 s | 1.48–2 s |
| S at 10 In | 72 / 79 / 85 ms | 60–140 ms |
| I at I3 +15% | 12 / 11 / 14 ms | ≤50 ms |
| I at I3 −15% | No instantaneous trip | Must not trip |
The same certificate records contact resistance at 10 A of 14 / 10 / 13 µΩ, insulation resistance above 1000 MΩ at 500 V, contact wear under 20% and more than 30 mechanical operations. See the full sample ACB certificate.
When the trip unit has failed
A dead or out-of-tolerance PR unit does not mean a new breaker. The options are a tested PR unit from donor stock where one is available, a modern electronic trip unit fitted inside the Emax frame and set to the original characteristic, or ABB's Emax 2 retrofit. The first two keep the cradle, the secondary wiring and the settings. Whichever route, the breaker is injection-tested at your settings before it ships.
Frequently asked questions
Why is my PR122/P display blank when the breaker is in service?
The relay powers itself from the breaker's current sensors only above a minimum three-phase current, roughly 100 A on E1–E3 and 200 A on E4 and E6 according to ABB's manual. Below that, it needs a 24 V DC auxiliary supply, a PR120/V module or a PR030/B battery unit to light up. If it stays blank with auxiliary power present, the relay has failed.
Which ABB test units work with PR121, PR122 and PR123?
ABB lists the PR010/T test unit and the Ekip T&P PC interface for these relays. Both connect to the test connector on the front of the trip unit. The PR010/T can run automatic, manual and trip tests on its own.
Is secondary injection enough, or do I need primary injection?
Secondary injection proves the trip unit's pickups and time delays. Primary injection also proves the current sensors and wiring by passing real current through the poles. Secondary injection is the standard workshop proof of the relay; primary injection is the stronger check when sensor or wiring faults are suspected.
What does the "TC disconnected" alarm mean?
The relay has detected that its trip coil is disconnected or faulty, so it cannot open the breaker on a fault. Treat it as urgent and check the trip coil and its connection.
Can you repair UL-listed Emax "-A" breakers?
Yes. Our sample certificate is for an Emax E3N-A, a UL-listed power circuit breaker built to ANSI C37.13. We repair and test these breakers; we do not re-certify UL listings.
For the faults we see on the whole breaker, not just the trip unit, see our Emax E1–E6 repair page. To get a first answer, send the nameplate, a photo of the trip unit and the alarm or fault through request a quote.
Send us the nameplate
A photo of the nameplate and the fault is enough for a first answer. We reply the same working day with a recommendation and a price for diagnosis and freight.