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This blog covers the technical features of spring-loaded and push-in terminals, and both the advantages and disadvantages of these technologies when it comes to installation practices, commissioning, footprint and authorisation for the North American market. The article then compares theoretical analysis with the results of a practical test, which clearly demonstrates how push-in technology can save an impressive amount of time.
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 type of connection technology is the screw terminal, which is increasingly now being replaced by the spring-loaded terminal and its successor, the push-in technology.
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In spring-loaded terminals, often also referred to as cage terminals, the conductor is fixed in a retaining profile using a spring. The spring can be opened using a tool, which needs to be inserted into an operating slot. This allows both flexible conductors (with or without ferrules) and solid conductors to be connected. The spring provides the required contact pressure and prevents the conductor from slipping out. In contrast to screw terminals, this avoids issues with the terminal not operating correctly due to too much or too little torque being applied when tightening the screws. The connection is based on a self-locking mechanism and is thus mechanically durable and electrically safe. Even when exposed to vibrations and shocks, spring-loaded terminals do not loosen by themselves and there is no need for regular maintenance.
Push-in technology is a further development of spring-loaded terminals. As such, in a plug-in terminal the electrical contact is also made and the conductor fixed in place using a spring. However, in the case of push-in technology, the spring will open if the conductor itself is pushed in—this means that rigid conductors or conductors with ferrules can be directly connected without the need for any tools. In order to open the spring and to connect flexible conductors without ferrules, push-in terminals also feature a mechanism that can be operated using a standard screwdriver.
Push-in terminals offer the same advantages as spring-loaded technology: The clamping force does not depend on the user, thereby avoiding issues with the terminal not operating correctly. As with spring-loaded terminals, the conductor is inserted and actuated from the front, which enables compact device designs and simplifies handling.
The disadvantage of spring-loaded terminals is that they cannot be operated without tools; therefore you always need both hands to make the connection. This takes time and, with large cross-sections, a lot of effort, as in this case the terminals have to be forced open, which risks causing damage. If the wrong tool is used, for example a cross-head screwdriver, the spring can also be irreparably damaged. While a screwdriver that is too small will not open the connection completely, meaning that the specified nominal cross-section cannot be accommodated.
These problems are eliminated when using push-in terminals. As with spring-loaded terminals, the conductor is inserted and actuated from the front, which enables 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. Practical tests show that wiring push-in terminals takes up to 40% less time compared to spring-loaded terminals.
Commissioning is also very simple. As push-in terminals can withstand even higher conductor pull-out forces than spring-loaded terminals, they remain extremely stable when exposed to vibration and shock loads and do not need to be retightened.
When it comes to the footprint, there is no difference between the different connection technologies—as seen in devices such as Eaton's contactors and motor starters. All motor-protective circuit breakers with a nominal current of up to 32 A are the same width and have the same footprint dimensions. This means that devices with spring-loaded terminals can easily be replaced with push-in models without having to alter the dimensions of the DIN rail or the control cabinet.
The same applies to approval for the North American market, because Eaton's motor-protective circuit breakers and contactors always comply with the standards necessary to be approved by IEC and UL, regardless of the connection technology. Whether users choose a device with screw, spring-loaded or push-in terminals therefore does not affect the options for worldwide use.
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. Not only did the result confirm the expected reduction in time compared to screw connections—it also resulted in a surprisingly high time saving of around 40% compared to spring-loaded terminals.
The explanation for this is relatively simple: To open the spring-loaded terminal's connection, a slotted screwdriver is required. This means that the user must always hold the conductor to be connected in one hand and the screwdriver in the other. Since there is no need for tools with push-in technology, the user can hold several conductors in one hand, which can then be inserted one after the other using the other hand.
In comparison with spring-loaded 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 post on the differences between push-in and screw terminals.
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