Guide · Siemens SENTRON 3WL / 3WA
Siemens 3WL vs 3WA: why the trip units don't swap
Siemens has replaced the 3WL with the 3WA. The frames are designed to fit the same switchboard space, but the electronics are new. A 3WA trip unit will not rescue a 3WL. Here is why, and what it means if you want to keep your 3WL in service.
The 3WL and its successor
The Siemens SENTRON 3WL is an air circuit breaker family in three frame sizes, from 630 A to 6300 A. Its electronic trip units are the ETU15B, ETU25B, ETU27B, ETU45B and ETU76B, each fitted with a rating plug, and the breaker talks to its accessories and communication modules over Siemens' CubicleBUS. You find 3WL breakers in US switchboards, data centers and in the bases of European-built wind turbines.
The SENTRON 3WA is its successor. Siemens describes it as built on the proven design of the 3WL, and markets it as an easy retrofit into switchgear that already holds a 3WL, with the same dimensions and connection points. Siemens began phasing out the 3WL in October 2023, and has published further milestones that wind down supply of new units and spares over the following years.
So the OEM path for a failed 3WL leads to a 3WA. That is a reasonable path. It is not the only one.
Why the trip units don't swap
It is tempting to think that if the frames fit the same space, the trip unit is the easy part. It is the opposite. Siemens says plainly that the 3WA's electronic components were completely redeveloped. In practice:
- Different trip-unit family. The 3WA uses the ETU600 and ETU800. These are not interchangeable with the 3WL's ETU15B to ETU76B. A 3WA trip unit does not fit a 3WL breaker, and a 3WL ETU does not fit a 3WA.
- Different internal bus. The 3WA uses CubicleBUS², a development of the 3WL's CubicleBUS. Siemens' 3WA communication manual states that the two are not compatible with each other. Communication modules, metering and external bus modules on a 3WL do not carry across.
- Different settings and parameters. A 3WA trip unit is set up with its own parameters and software. Your 3WL settings have to be translated, not copied, and the protection coordination needs checking again.
The practical result: there is no partial upgrade. You cannot fix a failed 3WL by fitting a 3WA trip unit. The OEM route replaces the whole breaker, and with it the trip unit, the bus modules and the settings.
What swapping to 3WA involves
Fitting a 3WA in place of a 3WL is a real project, even with good mechanical compatibility:
- A new breaker at new-breaker prices, on the OEM's lead time.
- New trip-unit settings, entered and checked against your coordination study.
- Replacement of 3WL communication and bus modules with 3WA equivalents if you use metering or remote monitoring.
- Changes to secondary wiring and controller interfaces where signals differ.
- Commissioning and testing on site.
For a new switchboard or a planned upgrade, that work is part of the plan. For a single failed breaker in a turbine or a critical board, it can turn a breakdown into a lengthy project.
Repairing a 3WL and keeping it
Most 3WL failures are not in the parts that make a 3WL a 3WL. They are in parts that wear, and those can be rebuilt:
- Secondary connector. The block of pins at the top of a drawout unit carries every control and trip signal. Racking and vibration damage the pins, and an intermittent pin looks exactly like a random trip-unit fault.
- Mechanism. After 15 years or so the grease hardens, closing slows and the breaker eventually refuses to latch. Corrosion can seize it completely.
- Motor operator and solenoids. These reach end of life on high-operation duty.
- Auxiliary switches. They go intermittent and send false position and ready-to-close signals.
- Contacts and arc chutes. Main and arcing contacts erode, and arc chute splitter plates wear.
- ETU and rating plug. Display failures, rating plug faults and drift.
A workshop repair strips the breaker to the frame, rebuilds the mechanism, replaces motor operators, solenoids and auxiliary blocks, renews contacts as needed, and restores or replaces the secondary connector and the wiring behind it. The trip unit stays in the 3WL family. A faulty ETU is replaced with a tested 3WL unit, and an upgrade within the family, such as an ETU25B to an ETU45B for its display and ground-fault function, is a workshop job too.
The repaired breaker goes back into its own guide frame with the same trip-unit family, the same CubicleBUS modules, the same wiring and the same settings. It is secondary-injection tested across every enabled protection element at your settings, and contact resistance and insulation resistance are recorded on the certificate.
A real example
A 2500 A 3WL with an ETU45B trip unit came to us from a wind farm in the United States. The mechanism was seized solid, with corrosion through every link and pin, broken internal moldings, a snapped charging handle and carbon on pole L1 up into the arc chute. It was stripped to the frame, every part cleaned individually, the broken parts replaced and the mechanism rebuilt. The ETU45B was secondary-injection tested and contact and insulation resistance were recorded. It spent four days in the workshop and went back by air with its certificate.
How to decide
Repair the 3WL when the switchboard is staying, the breaker is one of several 3WLs you want to keep consistent, or you cannot wait for a new breaker and the commissioning work. Move to 3WA when the board is being upgraded, you need features only the 3WA offers, or your site standard calls for current-production equipment. If the strip-down shows the breaker is not worth repairing, we will tell you before any work starts.
Frequently asked questions
Can I fit a 3WA ETU600 or ETU800 trip unit to a 3WL breaker?
No. The 3WA trip units are a different family from the 3WL's ETU15B to ETU76B and are not interchangeable. The internal bus is different too: Siemens states that the 3WA's CubicleBUS² is not compatible with the 3WL's CubicleBUS.
Does a 3WA fit where a 3WL was?
Siemens designed the 3WA for retrofit into switchgear with a 3WL and highlights matching dimensions and connection points. The breaker, trip unit, bus modules and settings are all new, though, so it still needs engineering and commissioning.
Is the 3WL still made?
Siemens began phasing out the 3WL in October 2023 and points customers to the 3WA. Supply of new 3WL units and spares is winding down, which is why repair of existing units matters.
My ETU shows a fault but passes injection testing. What is wrong?
Check the secondary connector and the wiring behind it before the trip unit. On a 3WL, an intermittent pin in the connector produces exactly this pattern, and it is a repair, not a replacement.
Can you upgrade a 3WL trip unit?
Yes, within the 3WL family. An ETU15B or ETU25B can be upgraded to an ETU45B or ETU76B for ground-fault protection, metering and communications. The new unit is set to your protection settings and injection-tested at them.
For the full list of 3WL faults and how each unit is tested, see our Siemens 3WL repair page. To start, send the nameplate, the ETU type and the 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.