Screw terminals vs spring cage

Home Electrical Engineering Forum General Discussion Screw terminals vs spring cage

  • This topic has 7 replies, 6 voices, and was last updated 9 years ago by Anonymous.
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    John Morris

    I’m not sure if this topic will be of interest to your readers, but we are a switchboard manufacturing company that has always used
    conventional screw type rail connectors for field connections to control wiring.

    At present we are hearing a lot about cage clamp terminals (screwless) from our suppliers and we considering whether or not it would be a good idea to change, as some of our customers are specifying these.

    I would be interested in any experiences and opinions from your readers as to which they have found to be best overall. Maybe it is the case that one type is better for certain applications or in particular instances? I would also be interested in any experiences relating to the larger cage clamp terminal with regard to current carrying capability.




    The “problem” with conventional screw type terminals is that even if properly torqued at installation time, it might loosen, especially whenever there are vibrations (AC power is already a reason for vibrations, I believe, but also on applications with vibrations, like marine, large presses), or significant changes of temperature (motors which are on then off for some time …).

    And this loosening problem (I should also mention bad connection at installation time) remains an important risk, which can end-up in down-time and loss of production, or in the worst case may start a fire … This is generally prevented through regular maintenance, either to re-tighten the terminals or thermal imaging, sometimes vibration measurement to check the risk of loosening an thus reduce if needed the time between maintenance campaigns.

    When you use cage clamp terminals, in my experience, the huge advantage is that you don’t have to worry anymore because they won’t “loosen”. I believe this can be an advantage even for you as switchboard manufacturer, as it reduces the risks during its on-site usage. And it probably has other advantages of interest for you, like quicker connection, no or less risk of loose connection at assembly time …

    I didn’t see and don’t know about any problem related to their usage, so my advice would be: go for it !

    Regarding larger cage clamp terminals, I believe it is the same advantages but have less experience.





    I have no field experience about screwless terminals, but I use to visit a lot of electrical exhibitions and I can tell you that they get more and more popular.

    In fact, this technology is not new. I think it started 30 years ago, pushed by Wago company designing a connection using a “spring” in place of screw and registered as “cage clamp”. 



    My experience too with Cage Clamp Terminals is that they are far better than Screw Terminals.


    Some years ago we produced panels for Sony Outside Broadcast Vans .

    We only used WAGO spring clamp terminals , terminating up to 25mm cables  with great sucess ,easy to terminate cables and no problem with vibration .

    We still use them today ( cost permitting) mainly the Weidmuller ones and would thoroughly recomend them.


    An other big advantage is that one doesn’t need Cord End terminals to end a flexible (stranded) cable.

    Flexible cable in a screw clamp will losen after a while because the thin wires will reorganise themselves. Especially under influence of vibrations. In Belgium it’s even not aloud to use flexible cable in a screw clamp without Cord End terminals.

    Flexible cables in cage clamps give no problem since the spring permanently tightens the cable.

    Cage clamps are also faster, but they are more expensive.

    I have only used WAGO cage clamps (up to 95mm²) and have had no negative experience with them.


    As long as the frequency range at the location of installation of the panels in which the termianls are installed does not fall under the natural frequency of vibration, in which case there will a tendency for opening up of the connection, it is very good arrangement. Most of the off-shore installation does not prefer this arrangement, as the vibration levels are in very wide range and short distance.


    I used to hate spring terminals until someone actually sat me down and explained to me how they worked and what the differences were. It was always confusing for me to figure out whether a terminal was leg spring or spring cage. Now I will always prefer spring unless my customer specifically asks for screw (and I cannot convince him otherwise). The PT terminals from Phoenix go up to 95sq mm also and would be my choice. Hope this helps!

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