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LOCC-Box - The safe and intelligent protection module for DC 24V circuits

The EN 60204-1 „Safety of machines, electrical equipment of machines” requests a suitable overcurrent protection against overload and short-circuit as soon as the current of a control circuit exceeds either the rated value of a component or the acceptable current load of a cable.

Requirements for a safe system

LOCC-Box: with 8.1mm width the smallest monitoring current module on the market

March 2 2010 Since the conventional installation with switch-mode power supply and automatic circuit breaker cannot fulfil these requirements for technical reasons, a noticeable change was affected towards electronic monitoring modules in the last years.


A solution would be ideal that runs optimally with capacitive loads, that recognises extremely fast an over-current or a short-circuit during operation and switches off selectively only the path concerned independently of the cable’s cross section and length. Certainly, such a system must store the error in order to avoid a danger by renewed switching on and make a fault diagnosis possible. The LOCC-Box system of the Friedrich Lütze GmbH & Co KG fulfils these requirements with additional intelligent functionalities.

LOCC-Box - practical and rational

LOCC-Box NET, software for control and diagnostic

Matching the real requirements for the shut-down characteristic, the LOCC-Box offers the feature of freely setting the current values within a range from 1A to 10A via switch. These current values in turn can be assigned 10 different characteristics via switch. These characteristics, computed according to the I2t function, contain the thermal and the magnetic tripping characteristics of an automatic circuit breaker. Thus fast down times can be realised with overload and 2ms in case of a short-circuit. While similar products do not distinguish between capacitive load and short-circuit because of an integrated current limiting, the LOCC-Box recognises automatically the real current status. It is the intelligent evaluation that enables the setting of minimal rated values despite high inrush currents.


Beside the conformal over-current protection according to EN60204, the LOCC-Box offers all necessary diagnosis functions as standard. So the extent of utilisation of the path is indicated via LED. In case of a tripping by over-current or short-circuit, a fault message is made by a Desina conformal DC24V signal beside an indication by LED. The single fault signal can be simply extended to collective ones by jumpers. The restarting (after tripping or manual stop) is made then either by a keystroke on the box or electronically by a control system.

LOCC-Box in association with communication networks

Ralf Coors is Head of the Product Management Industrial Automation at Friedrich Lütze GmbH + Co.KG at Weinstadt

However, the demand for optimised installation, start-up and above all the fault diagnosis, makes it mandatory to directly integrate also protection elements into the system communication.


The LOCC-Box Net offers a comprehensive net and equipment analysis. Evaluated can be current, supply voltage, cause of a tripping, number of the tripping processes and operating hours.


The assembly of the network is made by gateways connecting to superordinate communication systems such as USB, RS232, CANopen and ProfiNet. Altogether 255 LOCC-Boxes can be operated at a single gateway.


Your email to ralf.coors(at)


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