Auxiliary releases

Auxiliary releases allow remote electrical tripping of the circuit breaker. They can be used to monitor control or main circuits in order to implement a protective system against accidental restart following a power failure, for example.

Auxiliary releases therefore perform a main circuit monitoring function in addition to the main circuit monitoring performed by the trip unit.

Auxiliary releases are extremely easy to install. No tools are required because these 21 mm wide components are simply snapped into place in the accessories compartments to the left and right of the handle. The accessories are connected by screw terminals for auxiliary conductors with a cross-section of up to 1.5 mm2. The terminals are mounted on the front of the unit for easy access.

The shunt trips are suitable for use in electrical interlocks. An attempt to switch on a circuit breaker while the interlock voltage is applied to the shunt trip leads to a so-called "no-load switching operation", i.e. the basic breaker always returns to the TRIP position and the main contacts never close.


All auxiliary releases are reverse-polarity-protected.

Shunt trips left STL


Shunt trips of type STL can be fitted in the left-hand accessories compartment as an alternative to an undervoltage release. The units are available with five rated voltages in the following range:

  • 24 to 600 V AC 50/60 Hz

  • 12 to 250 V DC

They have a maximum power consumption of 58 VA which is significantly lower than the power consumption of the flexible shunt trip versions.

Switches (permanent signal) or buttons (minimum signal duration 40 ms) can be used to control shunt trips.

Shunt trips flexible STF


Shunt trips of type STF can be fitted in the left-hand and the right-hand (3VA2 only) accessories compartment. They are therefore suitable for combining different auxiliary releases in one switch.

The units are available with six rated voltages in the following range:

  • 24 to 600 V AC 50/60 Hz

Due to their design, their power consumption ranges up to maximum 750 VA and is therefore higher than the power consumption of STL versions.

Undervoltage releases UVR


Undervoltage releases trip the molded case circuit breaker in the event that the rated voltage fails or drops to between 70 % and 35 % of its normal value (in compliance with the relevant standard).

The main contacts of the basic breaker cannot be reclosed until the rated voltage of the UVR reaches 85 % of its normal value. The breaker main contacts cannot close until the UVR rated voltage reaches this level.

The units are available with rated voltages in the following range:

  • 24 to 480 V AC 50/60 Hz

  • 12 to 250 V DC

Undervoltage releases with leading NO contacts UVR (LNO)


The UVR release is protected against open circuits when combined with an EMERGENCY STOP pushbutton. The two installed NO (auxiliary) contacts allow the control circuits to be isolated after the breaker has tripped. The undervoltage release with leading NO contacts UVR (LNO) is therefore an ideal component for installation in the EMERGENCY STOP circuit of a 3VA molded case circuit breaker or switch disconnector as the main switch for a machine or installation. Safe disconnection of the main current paths and safe isolation of the EMERGENCY-STOP circuit requires the molded case circuit breaker to be switched OFF.

Universal releases UNI


A universal release is a single, 21 mm wide component in which a shunt trip and an undervoltage release are combined. These are subject to the same tripping conditions as the individual devices. A single component with minimal footprint can therefore perform both functions.

The three available rated voltages are identical in each case for both the shunt trip and the undervoltage release. These rated voltages are:

  • 12 V DC

  • 24 V DC

  • 48 V DC

Technical specifications of shunt trips and releases


3VA molded case circuit breakers


EMERGENCY-STOP pushbutton (to be provided by customer)


Undervoltage release with leading NO contacts