Auxiliary and alarm switches

The auxiliary and alarm switches for 3VA molded case circuit breakers belong to an integrated range of accessories. They can be installed in all sizes of all breakers up to 630 A.

The auxiliary and alarm switches can be very simply snapped into place and connected up in accessories compartments provided on the front panel of the unit to the left and right of the handle.

All auxiliary and alarm switches are designed as changeover contacts and therefore provide a high degree of flexibility for planning and installation purposes.

HQ and HP switches

The switches are available in versions HQ and HP. HQ switches are 7 mm wide, and HP switches 14 mm wide.


Both switch versions can be combined extremely flexibly in a molded case circuit breaker. This level of compatibility means that two HQ switches can be optionally installed in place of one HP switch.

HQ and HP switches have the same functionality, but differ in terms of the following features:

  • Connection technology

    • HQ: One conductor per contact point

    • HP: Two conductors per contact point possible (loop-through)

  • Key electrical data

    • HQ: max. 250 V; max. 6 A

    • HP: max. 600 V; max. 10 A

Individual key electrical data can be found at the end of this chapter.

All HQ switches are also available in a version compatible with electronic circuitry (HP el).

The diagram below uses the example of an ET200S to illustrate the conventional method of connecting the electronics-compatible auxiliary switch AUX, the trip alarm switch TAS and the motor operator MO320 to a distributed I/O unit.

Further information about contact reliability can be found at the end of this chapter.

Auxiliary switches AUX


The purpose of auxiliary switches is to signal the position of the main contacts of the molded case circuit breaker. The contacts of the auxiliary switch open and close simultaneously with the main contacts of the molded case circuit breaker.

Leading changeover switches LCS


Leading changeover switches signal the opening of the main contacts with a lead time of 20 ms in advance of circuit breaker trips and are thus used for load shedding, for example.

Trip alarm switches TAS


Trip alarm switches signal every circuit breaker trip, regardless of the cause of the trip. The trip alarm switches are operated whenever the molded case circuit breaker switches to the TRIP position.

Electrical alarm switches EAS


Electrical alarm switches are operated as soon as the main contacts of the molded case circuit breaker open in the event that the breaker is tripped by the ETU. They indicate the following conditions:

  • Overload L and neutral conductor overload

  • Short-circuit S, I

  • Ground-fault tripping G

  • Residual current device RCD820

The electrical alarm switch is not operated:

  • When the breaker is tripped manually


    • When the breaker is withdrawn from the plug-in/draw-out socket when the main contacts are closed

  • When activated via an auxiliary release

    • Shunt trip STL, STL(EI), STF

    • Undervoltage release UVR, UVR (LNO)

    • Universal release UNI

Electrical alarm switches are compatible only with 3VA2 molded case circuit breakers equipped with electronic trip units (ETU).

Short circuit alarm switches SAS


Short circuit alarm switches signal trips only if they have been initiated by a short circuit. These events are also indicated on the molded case circuit breaker.

The trip must be reset by deliberate acknowledgement of the fault before the molded case circuit breaker is switched to ON again.

Short circuit alarm switches are only compatible with 3VA1 molded case circuit breakers. On breakers equipped with electronic trip units, the short circuit alarm function is performed by the electronic trip unit (ETU) and the EFB300 external function box.