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In this blog post we'll look at the features of screw and push-in terminals, and both the advantages and disadvantages of the two connection technologies. In order to make this clear, we will also present the results of a practical test, which conclusively confirm the advantages of push-in terminal technology.
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Terminals are detachable connections that are used to permanently connect electrical conductors to each other or to other equipment, both mechanically and electrically. They make it possible for you to wire switchgear systems quickly, simply and safely. But when doing so, the choice of terminal technology is vital in determining the efficiency of the associated processes over the entire life cycle of the system. The oldest and most frequently used type of connection technology is the screw terminal, which is now increasingly being replaced by the spring-loaded terminal and its successor, the push-in terminal.
Screw terminals are available in a variety of designs. What they all have in common is that the terminal mechanism needs to be actuated by means of a stud screw. In this process, the conductor is pressed or clamped firmly against a latch made of a copper alloy. This is done perpendicular to the screw, usually from above or below, but to do this you require enough space.
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Push-in technology is based on plug-in terminals, in which electrical contact is made and the conductor is fixed in place using a spring. The spring is opened by pushing in the conductor itself: Rigid conductors or conductors equipped with a ferrule can be directly connected without the need for any tools. In order to open the spring and connect flexible conductors without ferrules, push-in terminals also feature a mechanism that can be operated using a standard screwdriver. The clamping force does not depend on the user, thereby avoiding issues with the terminal not operating correctly. In addition, the conductor is inserted and actuated from the front, which enables compact device designs and simplifies the handling of the push-in connection.
With screw terminals, applying the correct torque when tightening the screws is crucial to safely clamping the conductor. If the clamping force of the screw is too high, you run the risk of the soft copper used in the conductor wire being damaged. What's more, the thread may crack or the screw head may be damaged, which can cause irreparable damage to the terminal. However, if the applied torque is too low, the clamping force will not be sufficient and the conductor may come loose. This puts the electrical connection at risk of being lost, and in a worst case scenario could cause the terminal to "burn out" due to the increasing contact resistance and the associated temperature rise.
These problems are eliminated when using push-in terminals. Instead of being inserted from above, the conductor is inserted from the front, which allows for compact device designs and simplifies handling. However, the USP of push-in technology is that it enables the direct, tool-free insertion of conductors. The conductor can be inserted and connected with just one hand. This means even users with less technical knowledge can safely install push-in terminals.
Commissioning is also very simple. While it is often recommended to tighten screw connections during commissioning—an important time and cost factor—push-in terminals can withstand significantly higher conductor pull-out forces. This means they remain extremely stable when exposed to vibration and shock loads and are considered maintenance-free.
To test the reliability of push-in connections, Eaton commissioned the independent testing laboratory I²PS to carry out some tests. Not only did these tests reveal that the connections are vibration-resistant—they also demonstrated that push-in terminals guarantee a gas-tight electrical connection even in a highly corrosive atmosphere. At the same time, the series of tests was also able to eliminate the preconception that push-in terminals supposedly heat up under load more than screw terminals. In fact, I²PS has proven that in some cases, push-in connection technology even has a lower temperature rise than screw connections.
Eaton has conducted a series of tests in collaboration with switchgear and control system manufacturer Hanseatic Power Solutions (HPS) to test the productivity and time savings offered by push-in technology under real conditions. The result? Push-in terminals offer a time saving of 50% in comparison with screw terminals. What's more, the use of switchgear with push-in connections can significantly reduce downtime when replacing defective devices.
In comparison with screw terminals, push-in terminals are not only easier to handle, but also offer significant time and cost advantages over the entire life cycle of a system—as a result, any additional costs for devices using this kind of connection technology very quickly pay for themselves. More information on this topic can be found in the Eaton white paper "Wiring more efficiently from start to finish" and in our blog article on the comparison between push-in and spring-loaded terminals.
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