Short circuit protection concepts with Push-in fuse terminal blocks
Every systems manufacturer – from machine building to process engineering – should be concerned with the issue of “fuse protection for circuits”. Whether it is a matter of protection against overloads or short circuits – fuses protect devices and cables from failure. The fuse elements in use today have scarcely changed in many years. Anyone who would nevertheless like some savings when wiring circuits opts for fuse terminal blocks with Push-in connection.
Fuses – tried and tested for a long time
Fuses are one of the first components that were developed in the history of electrical engineering. Thomas Alva Edison is considered to be the inventor who, in 1880, had the idea to protect an electrical circuit with a predetermined breaking point, and filed a patent on this idea. In the event of overload, the electrical current is concentrated on a defined point by intentionally narrowing the cable cross-section in the circuit. This basic principle is still used today in almost any fuse element.
It is the task of the fuses to protect devices, systems, and cables from failure. In the event of a short circuit in the circuit of a device, for example, a brief overcurrent causes the fuse element to trip and the circuit to open before the device can be damaged. In this case, it is vital that the fuse element as well as the corresponding fuse carrier – a fuse terminal block, for example – are perfectly suited to the application.
In machine building and systems manufacturing, type 5 x 20 mm and 6.3 x 32 mm cartridge fine fuses have become established. They are more and more used when reliable and accurate protection is required. Thanks to the large number of available fuse types – fast blow or slow blow, sand-filled, in glass or ceramics housing -, cartridge fuses are available in almost any version and for any requirement. The format of the fuse-links is standardized globally and has hardly changed in the last 70 years since its first definition in DIN 41571.
New fuse terminal blocks with Push-in connection technology
Matters are quite different when looking at the counterpart – the fuse carrier. Driven by trends such as cost-efficiency and miniaturization, totally new fuse terminal blocks have been developed. In this context, Phoenix Contact has also extended its product range successively. The new range comprises 4-mm² multi-level fuse terminal blocks for holding type 5 x 20 mm cartridge fuse elements, and 6-mm² fuse terminal blocks for type 6.3 x 32 mm cartridge fuse elements. All the series have knife disconnect terminal blocks and disconnect terminal block of the same shape for component connectors. In this way, any application can be designed universally.
The new fuse terminal blocks are equipped with easy Push-in connection technology that is widely used. Compared to other established connection technologies, Push-in technology has numerous advantages. Push-in technology works based on the pressure spring principle – the conductor can be plugged in directly without having to open the terminal point first. Thanks to the sophisticated spring principle of the high-alloy steel spring that pushes the conductor against the current bar, the conductor can be mounted with up to 50 percent lower insertion force. This considerably reduces the wiring time – both the builders and the operators save costs.
The multi-level terminal blocks also offer savings potential, thanks to their compact dimensions. Using conventional wiring methods of sensors and actuators, the power supply and the divisible signal path are wired separately on adjacent feed-through terminal blocks. Additional space is required for the ground potential of the conductor shield. Large distances to the control box also call for larger conductor cross-sections. A terminal block series has been developed for these requirements: PT 4-PE/L-HESI. In the past, at least five terminal blocks were required to fulfill this task. Today, however, this type of connection only requires one pair of terminal blocks: one multi-level fuse terminal block and one knife disconnect terminal block of the same shape. Thanks to a pitch of 6.2 mm, space savings of 18.6 mm can be achieved, i.e., 66 percent when compared to the standard 31 mm. The comprehensive range of accessories of the CLIPLINE complete terminal block system can additionally be used for clearly marking the terminal blocks. Furthermore, potentials can easily be distributed using jumpers and two bridge shafts on each level.
Automotive flat-type fuses in machine building and systems manufacturing
It is not only the fuse terminal block connection that needs to be simple and intuitive. Operation and replacement of a defective fuse element, too, should only take a few seconds. Because time plays a major role, flat-type fuses are used in the automotive field but also in machine building and systems manufacturing. To meet this demand, Phoenix Contact has designed a fuse terminal block holding compact type C fuses according to ISO 8820-3 or DIN 72581-3.
The fuses are color-coded depending on the current strength and available worldwide. The fuses are only available for low voltages up to 48 V but the standardized fuse carrier can be used for other purposes and also for higher voltages up to 250 V AC. The standardized flat-type fuse socket can hold thermal circuit breakers (TCP for short) that convert a fuse terminal block into a miniature circuit breaker. In addition to the high nominal voltage, the thermal circuit breakers also have other advantages. These automatic devices can be switched on again and current paths can be enabled using an operating element. In contrast, fuses cannot be repaired and need to be replaced after tripping.
Another advantage is the overall width, which is significantly smaller than that of conventional miniature circuit breakers, which means that a lot of space can be saved in the control cabinet. The PT 6-FSI/C fuse terminal block has a nominal cross-section of 6 mm² and is also suitable for a nominal current of up to 30 A – a performance range for operation of numerous electrical devices.
- By Moritz Krink, Product Marketing Modular Terminal Blocks, Industrial Cabinet Connectivity Business Unit, Phoenix Contact GmbH & Co. KG, Blomberg, Germany