Thermal imaging or retightening wire terminals, seriously?

Thermal ImagingReading some forum discussions around loose electrical connections, it is obvious there are two camps of thoughts: one promotes regular retorquing or retightening of the wire terminals, while the other calls for thermal imaging.

But I guess the question is not even about retightening or thermal imaging of wire terminals …

Loose electrical connection is definitely a big risk, and if not avoided or detected will result in over-heating, internal arc or fire inside electrical equipment. How to avoid such hazards?

On one hand, regular retorquing of screw terminals could create overtorquing conditions, worsening the condition of the electrical connection.

And on the other hand, thermal imaging requires dedicated skills and tools, and could have anomalies or impossibilities: all electrical apparatus have to be operational and at the nominal load, and accessing measurement points could bring safety issues.

But why to try to eliminate the consequences and not the root causes?

The best, in my opinion, is to eliminate the root causes and it is possible to do so by using devices with maintenance free terminals (spring cage or cage clamp types).

I really wonder why this type of wire terminals is not more regularly used. What do you think?

As a designer, do you generally specify the use of spring cage terminals in your tender specifications?
And if not, why?


  • I’m fully in favour of spring clamps such as by WAGO. I find the reluctance to using spring clamps is the status quo mind set, dislikes change.

  • This is a very interesting post. If you ask me about what kind of wire terminals are the best, my opinion is that spring cage or cage clamp conectors are clearly better than screw terminals, because of their installation ease and their operational safety. But, as in many other issues in electrical engineering, there is a factor that can’t be forgotten: the habits, which are not always easily changed in favour of technical advances. Therefore, it’s a fact that screw terminals continue to be extensively used, and, at this point, thermal imaging provides by far the best solution for preventive maintenance. Even if you use cage clamp terminals, thermal imaging continues to be a very valuable tool for potential failures detection.

  • Colleagues, It appears we’ve been experiencing the same phemonena on others changing or not to the use of spring clamp. Very interesting. My vote is certainly for spring clamps, for speed and stability of terminations. Thermal imaging is great.

  • “if the design of the electrical installation is not good, sub dimension the section of wire, over dimension of MCB (and generally all other type of protective device), low quality products, because of the limited knowledge of technical requirements, the result is overload in the end of the installation.
    Doesn’t matter if you use cage clamps (“new tech”) from whatever producer and any other product you think, the reason of heating the point of defect is important, and is a mast to find reason of defect.
    So in my opinion is good the new technology – thermal imaging, to find the points of defect before is happening the defect, but of course good quality products could increase the time of appearance of defect.
    About retightening of connectors, is written in the standards to be done at a moment in the life of a product.
    By the way the difference between the cage clamps and screw connectors is the price – not the habits like someone suggested.

  • What nobody has mentioned is that a thermal survey will not just detect loose connections but also high resistance in switchgear contacts, crimps and plug / sockets. Re-torquing will never prevent these high resistance problems.

    In my opinion a thermal survey is the most cost-effective and least intrusive way of checking that everything is working well and probably the least likely method to cause and knock-on problems with network reliability.

  • I have no issue with spring cage terminals for PLC or low voltage, low current control wiring but have doubts about their ability for higher current applications. I have never seen contact resistance comparison data but the deformation of the conductor that a screw terminal produces must give a higher contact area (and hence lower resistance) than a spring terminal. So, spring terminals OK for low current, screw terminals for high current.

  • In process industry where only way to check looseness is by measurement of temperature by infrared temperature meter.

    Is there any better way?

    • ALAM,

      In my opinion there’s no better way for checking looseness than thermal imaging. It’s safe, it’s reliable and it can be used with the production process fully operating. The only issue to take into account is that the inspection should be always done by a certified infrared thermographer, so you can be sure about the results reliability

  • I agree with Simone. Infrared scanning is a very effective tool providing that the person behind the IR imager is trained and certified. Another effective technology for detecting loose electrical connections is a product called Delta T Alert. It monitors the delta t between the electrical enclosure temperature and the ambient room temperature in which the enclosure is located. The delta t information is transmitted to an onsite computer wirelessly for analysis and trending. You can check out the website at

  • We have what we call preventive maintenance in electrical circuits,where we do retightening,cleaning, electrical terminal at a given interval of time.This is being done to prevent looseness,carbon from being formed on the electrical contacts.On doing this will protect your circuit from overheating which might result into electric fire.

  • Retightning and cleaning electrical connections while useful is also time consuming, disruptive and can also cause problems.

    The image at the top of this thread is one of my images and we are thermal imaging consultants so obviously are slightly biased towards this type of technology but it is wort noting that overtightning of connections and terminations is also a cuse of many failures.

    Very often we identify faults with poor connections and recommend that the client removes the connection, cleans and then replaces. However what happens a lot is that electricians just give it a good hard tighten which can actually make things worse and very often does (we go back and re-look at the connection an hour or so later).

    Overtightning can distort the contact surfaces and therefore reduce the contact area of the connection.

  • Great questions and a really important discussion! I think that no matter what type of clamp you use, there’s always the risk of something going wrong and it being undetected. There will always be a need for thermal imaging and preventative maintenance from companies like Thermoscan.

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