In brief
A terminal block is a connecting element mounted on a DIN rail that securely and detachably connects conductors in a control cabinet.
Contents
What is Terminal block?
Terminal blocks form the interface between the internal wiring of the control cabinet and the cables to sensors, actuators and motors. They are snapped onto DIN rails side by side, linked with jumpers and identified with markers. Requirements for terminal blocks for copper conductors are described in IEC 60947-7-1, and for protective conductor terminal blocks in IEC 60947-7-2. They make testing, fault-finding and replacing cables easier.
By connection technology, a distinction is made between screw terminals, spring-cage terminals and push-in terminals, into which solid conductors can be inserted without tools. By function, there are feed-through, protective earth, multi-level, fuse, disconnect, test and sensor terminal blocks as well as terminal blocks with components such as diodes. Key ratings are rated cross-section, rated current and voltage, number of connection points, rail type and colour. Multi-level terminal blocks save space on the rail, while disconnect terminal blocks allow measurements without disconnecting the conductors.
Terminal blocks are inexpensive, but their failure can bring a plant to a standstill. Causes are loosened screw connections, overheated contact points, incorrect conductor cross-sections or damaged terminal housings. Accessories such as jumpers, end plates and markers must match the terminal system. With screw terminals, the specified tightening torque should be observed.
In practice: maintenance and procurement
For replacement or extension, the manufacturer part number, connection technology, cross-section, function and colour as well as matching accessories are needed. It pays to standardise on a few terminal systems across the plant so that jumpers, end plates and markers remain interchangeable.
Synonyms and abbreviations: DIN rail terminal · feed-through terminal block · connection terminal · modular terminal block
Frequently asked questions
What is the difference between screw, spring-cage and push-in terminals?
With screw terminals, the conductor is clamped with a screw that can be retightened regularly. Spring-cage terminals hold the conductor by spring force; the spring is opened with a tool to insert it. With push-in terminals, solid conductors or conductors with ferrules can be inserted directly. Spring technologies are largely maintenance-free and vibration-resistant.
Which terminal block for which cross-section?
Each terminal block is designed for a specific rated cross-section and can accept conductors within a defined range around it. The cross-section depends on current, cable length and installation method. The terminal should match the conductor used; terminals that are too small can overheat, while terminals that are too large do not hold thin conductors securely.
What information is needed to reorder terminal blocks?
The manufacturer part number, connection technology, rated cross-section, terminal function, number of levels and connections, colour and rail type are needed. Matching accessories such as cross-connectors, end covers, end brackets and markers should also be stated, as these are usually system-specific. If terminals from different systems are mixed, jumpers and covers often do not fit.