Solid-State Switching Devices for Resistive Loads Solid-State Contactors General data ■ Overview The complete units consist of a solid-state relay plus optimized heat sink, and are therefore ready to use. They offer defined ra- ted currents to make selection as easy as possible. Depending on the version, current strengths of up to 88 A are achieved. Like all of our solid-state switching devices, one of their particular ad- vantages is their compact and space-saving design. With their insulated mounting foot they can easily be snapped onto a standard mounting rail, or they can be mounted on sup- port plates with fixing screws.
This insulation enables them to be used in circuits with protective extra-low voltage (PELV) or safety extra-low voltage (SELV) in building management. For other ap- plications, such as for extended personal safety, the heat sink can be grounded through a screw terminal. The solid-state contactors are available in 2 different versions: • 3RF23 single-phase solid-state contactors, • 3RF24 three-phase solid-state contactors 1) The miniature circuit breakers can be used up to a maximum rated vol- tage of 480 V! Version for resistive loads, "zero-point switching" This standard version is often used for switching space heaters on and off.
Version for inductive loads, "instantaneous switching" In this version the solid-state contactor is specifically matched to inductive loads. Whether it is a matter of frequent actuation of the valves in a filling plant or starting and stopping small operating mechanisms in packet distribution systems, operation is carried out safely and noiselessly. Special "Low noise" version Thanks to a special control circuit, this zero-point-switching spe- cial version can be used in public networks up to 16 A without any additional measures such as interference suppressor filters.
As a result it conforms to limit value curve class B according to EN 60947-4-3 in terms of emitted interference. Special "Short-circuit resistant" version ! "# "# ! "# Skillful matching of the zero-point switching power semiconduc- tor with the performance of the solid-state contactor means that "short-circuit strength" can be achieved with a standard minia- ture circuit breaker. In combination with a B-type MCB or a con- ventional line protection fuse, the result is a short-circuit resistant feeder. The setup and installation above can also be used for the solid- state relays with a I 2 t value of at least 6600 A 2 s.
In order to achieve problem-free short-circuit protection by means of miniature circuit breakers, however, certain boundary conditions must be observed. As the magnitude and duration of the short-circuit current are determined not only by the short-cir- cuit breaking response of the miniature circuit breaker but also the properties of the wiring system, such as the internal re- sistance of the input to the network and damping by controls and cables, particular attention must also be paid to these parame- ters. The necessary cable lengths are therefore shown for the main factor, the line resistance, in the table below.
■ More information Selecting solid-state contactors The solid-state contactors are selected on the basis of details of the network, the load and the ambient conditions. As the solid- state contactors are already equipped with an optimally mat- ched heat sink, the selection process is considerably simpler than that for solid-state relays. The following miniature circuit breakers with a type B tripping characteristic and 10 kA or 6 kA breaking capacity protect the 3RF23..-.DA.. solid-state contactors in the event of short-circuits on the load and the specified conductor cross-sections and lengths: The following procedure is recommended:
• Determine the rated current of the load and the mains voltage • Select a solid-state contactor with the same or higher rated current than the load • Check the correct contactor size with the aid of the rated cur- rent diagram, taking account of the installation conditions 25 Siemens · 2009 Rated current of the miniature circuit breaker Example of type1) Max. conductor cross-section Minimum cable length from contactor to load 6 A 5SY4 106-6, 5SX2 106-6 1 mm2 5 m 10 A 5SY4 110-6, 5SX2 110-6 1.5 mm2 8 m 16 A 5SY4 116-6, 5SX2 116-6 1.5 mm2 12 m 16 A 5SY4 116-6, 5SX2 116-6 2.5 mm2 20 m 20 A 5SY4 120-6, 5SX2 120-6 2.5 mm2 20 m 25 A 5SY4 125-6, 5SX2 125-6 2.5 mm2 26 m