With the right equipment and some basic understanding, it’s not hard to determine which connections are heating up
The previous posts in this series on power connections discussed the importance of tight connections, how and why they tend to get loose over time, and the dangers that arise when this happens. In this post, we explain how thermal imaging can be used to locate power connections in need of tightening without shutting off power.
Finding hot spots
The fact that loose power connections heat up is bad for safety and efficiency, but it does make it possible to locate a problem connection from a safe distance without making contact—and usually long before a failure occurs.
Thermal imaging technology has come a long way in recent years. Today small, handheld infrared cameras, as shown in Image 1, enable users to quickly obtain a more accurate temperature reading by simply pointing at an object. Software typically provides an enhanced, color-coded image so users can very easily determine what’s hot and what’s not.
A quick review
There are three main factors that are often the cause of electrical connections becoming loose—creep, thermal changes, and external vibration.
Creep is the name given to the reshaping of the conductor that happens naturally with the passage of time. This is permanent deformation, much like a heavily loaded bookshelf that doesn’t spring back into its original shape when the books are removed, see Image 2 reference.
Thermal changes in the conductor occur naturally, such as when current goes on and off, causing expansion and contraction.
External vibrations may come from heavy equipment operating nearby or any number of other factors. When present, it can be difficult if not impossible to avoid them.
To counteract the natural loosening of connections, Schneider Electric, for example, developed EverLink™ technology. Using spring elements built into the connection hardware, EverLink maintains the proper amount of pressure on the conductor despite the effects of creep, thermal cycling, and external vibration. Certified mechanically and electrically to meet the American standard UL489, EverLink terminals do not require periodic retightening.
However, because not all equipment incorporates this technology, maintenance personnel must still check connection efficiency.
Locating loose connections
Thermography is just one way to identify problematic connections, but perhaps among the easiest and quickest ways to do so. Here are a few considerations to be keep in mind:
- Capturing thermal images does not require any contact with the terminal, so it can be done without powering down the panel or circuit.
- To get an accurate picture of the connection integrity, the circuit should have been powered up at full current for some time before testing so that it has thermally stabilized.
- Other signs of thermal rise should still be noted. Discoloration of material—wire insulation or product material, for example—or odors may indicate an abnormal rise in temperature and the need for retightening.
- Thermal camera inspection campaigns are so effective they can effectively replace the periodic tightening campaigns that traditionally have been required.
- When loose connections are discovered, they should be retorqued to the original installation specification.
It is worth noting again that for a thermal imaging inspection to be effective, it is necessary for the installation to be thermally stabilized and operating at its maximum electrical draw. This requires systematically repeating inspections at different times because not all areas of a building are in full load at the same time.
In addition, if the inspection campaign occurs at the beginning of a connector’s loosening, the resistance in that connection may not be sufficiently degraded to generate significant heating, and in this case, the thermal camera would not detect the loosened terminal.
To learn more about how EverLink technology eliminates the need for retightening connections, download the white paper “How to ensure a secure, long-lasting power connection for your electrical installation.”
|Daniel Vanzetto is a senior inventor at Schneider Electric’s R&D center. He has strong experience as a terminal specialist and works at a global level on many new connecting solutions with major patents. He also works very closely with suppliers for launching new and interesting technologies, or to optimize existing designs. Daniel is one of Schneider Electric’s foremost authorities on connections.|