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Practical Electronics Editorial offices Electron Publishing (Aust.) Tel +61 2 9939 3295 Unit 1, 234 Harbord Road Email pe<at>pemag.au Brookvale NSW 2100 Web www.electronpublishing.com Australia Address mail to: Electron Publishing (Australia) PO Box 194, Matraville NSW 2036 Australia Advertising enquiries +61 2 9939 3295 pe<at>pemag.au Editor Nicholas Vinen Publisher Nicholas Vinen Digital subscriptions Stewart Kearn Tel 07918 614662 Online Editor Alan Winstanley Web Systems Kris Thain Production Bao Smith Technical staff Tim Blythman, John Clarke Print subscriptions Practical Electronics Subscriptions PO Box 6337 Bournemouth BH1 9EH Tel 01202 087631 United Kingdom Email pesubs<at>selectps.com Technical enquiries We regret that technical enquiries cannot be answered over the telephone. We are unable to offer any advice on the use, purchase, repair or modification of commercial equipment or the incorporation or modification of designs published in the magazine. Questions about articles or projects should be sent to the editor by email: pe<at>pemag.au Projects and circuits All reasonable precautions are taken to ensure that the advice and data given to readers is reliable. We cannot, however, guarantee it and we cannot accept legal responsibility for it. Some projects and circuits published in Practical Electronics employ voltages that can be lethal. Do not build, test, modify or fix any mains-powered equipment unless you fully understand the safety aspects involved and you use an RCD (GFCI) adaptor. Component supplies Silicon Chip Publications may offer kits or other parts for making our projects, but not in all cases. When kits are not available, readers will need to find and source parts themselves. We advise readers to check that all parts are still available before commencing any project in a back-dated issue. 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The laws vary from country to country; readers should check local laws. 2 Volume 54. No. 6 June 2025 ISSN 2632 573X Editorial Don’t tin wires going into terminal blocks This seems to be a slightly controversial and misunderstood topic. There is a temptation to tin the end of a wire before you insert into into a terminal block, especially a screw terminal. Doing so stops stray strands from sticking out and makes inserting the wire easier. However, there are serious problems with doing so, and you really shouldn’t. In fact, this practice is actively discouraged or even prohibited by most wiring standards, including BS 7671, AS/NZS 3000, and related IEC and UL standards. The problems relate to mechanical stability and long-term reliability. Unlike copper, solder is a soft metal with a relatively low melting point. Over time, especially in the presence of heat and pressure, it can ‘cold flow’ – gradually deforming under the clamping force of a terminal screw. This can lead to a loose connection, increased contact resistance and, in extreme cases, overheating or arcing. Also, when you insert a bare stranded wire into a terminal and tighten the screw, the strands compress and spread slightly. This creates a wide, gas-tight contact area, improving both electrical conductivity and mechanical grip. Tinning prevents that from happening. The solder locks the strands together, turning them into a pseudo–solid core that can’t adapt to the clamping surface. The result is a reduced contact area, less secure grip and higher resistance. Solder is also less conductive than copper, so the connection with the tinned wire not only has a lower contact surface area, but also higher inherent resistance. This makes for a potentially hot and unreliable joint. If you’re dealing with fine-stranded wire or worried about stray strands, the correct solution is not solder, it’s a ferrule. These are metal sleeves, usually made of tin-plated copper, that crimp over the end of a stranded wire to hold it together. A properly crimped ferrule allows the terminal screw to compress the ferrule itself, maintaining a secure, stable connection over time. It also preserves the benefits of a gas-tight contact. Ferrules are not expensive – decent kits with crimpers and assorted sizes are readily available. Once you try them, you’ll probably never go back. Nicholas Vinen, Electron Publishing (Australia)* Publisher & Editor, Practical Electronics Magazine * a division of Silicon Chip Publications Pty Ltd. Practical Electronics | June | 2025