Mains Plug Soldering Wires

Question

So I have a few extension leads all are 13A rated but the cable length is too short just 1 metre. It would be cheaper for me to rewire them than buying new extension leads.

I bought a reel of the correct cable rated for 13A and have rewired one. However just have a query in regards to the wiring itself at the plug end.

In regards to the wires in the plug end they were previously "crimped" with just a small piece of metal (the wire wasn't left bare) if that's the right term. I didn't want to leave the wire bare either and to ensure there is a good connection, so I soldered the wire ends and then was able to nicely secure them with the screw.

However I am now wondering whether there is any safety hazard to soldering the end of the wires like that at the plug end? In terms of potential heat leading the solder to melt?

May be a silly question but it just cropped up in my mind so better to ask.

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After reading and considering all replies, unfortunately I was unable to find small enough ferrules in standard stores even electrical ones, not sure whether that's mainly a US thing but it doesn't seem to be common in UK? They only had wire connector types but nothing as small to be used for the entry point holes for the wire on the plug. Sure could order online on eBay/Amazon but would be unsure of the quality.

So I left them bare rather than tinned with solder as seems like the safest alternative. Strands were secured properly. There won't be any pulling on the cable anyway as it is left stationary behind a desk.

Just to add the photo is a generic plug from Google. I done a much better job with the wire lengths (or so I hope!), as the question occurred to me after I had already soldered and been using the plug for a day or two.

Answer 1

Basically, this is in agreement with everybody else.

What you had were either uninsulated ferrules which are tubular, or a small piece of brass etc. crimped on to do the same job. These are basically the same as the aglets that you get on the end of shoelaces: they stop things fraying.

Using a ferrule is good practice whenever a screw connection is to be made, since they prevent loose strands from causing problems and- if used correctly- keep the strands parallel which is conducive to a good contact. While professionally they're applied using a crimp tool they don't have to be: a light squish with pliers to keep them in place after which, since they're very thin-walled, they will be deformed by the screws.

Ferrules, both insulated an uninsulated, are used heavily in control panel wiring and in some cases are mandated by industry standards. In the case of insulated ferrules the colour indicates the size, but there are at least two standards for this.

Photo from wikipedia (CC BY-SA 4.0)

Using solder to tin a wire which will then be held by a pressure connector (i.e. screw, clip etc.) is very bad news since the solder will creep with time, increasing the resistance of the joint and creating a fire risk. In addition, if the solder wicks up into the insulation it will damage it, incidentally stiffening the wire.

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Considering @Ariser's comment: I wonder whether a distinction has to be made between "soldered" (as in "tin/lead alloy soaked in between the strands") and "tinned" (as in "thin layer of pure tin on individual strands")? I think the bottom line is that it's possible to do the maths (and verify by testing) for something like uncontaminated strands laid straight, but once there's an indeterminate soft filler or strands are haphazardly crossed all bets are off. Hence things like the venerable https://workmanship.nasa.gov/lib/insp/2%20books/frameset.html : NASA engineers calculated what performance was attainable, then told technicians how to work in order to best approach that performance.

Answer 2

Solder cold flows so it can work loose and cause problems with overheating, charring etc. It's worse than leaving the wires as-is.

If you don't have ferrules, leaving them as-is would be a better option. Looks like they have a floating clamp plate (no! see below) so they should hold reasonably well so long as you get the strain relief clamping right (when you wiggle the cord, the wires inside should not move at all).

Answer 3

Solder makes the copper strands brittle and the flux may oxidize it.

It is not recommended to solder the wire ends. It likely ends up in loose connection under the screw which is a problem. This happens due to repeated thermal expansion and cooling, as you have got materials with different thermal expansion coefficients.

It is also not recommended to leave the strands as is, as tightening them under a screw will deform the strands and may make uneven connection with hotspots.

Best option (at least after those two) is to terminate the wire with crimp ferrules like in the original mains cables.

Answer 4

The original ends were likely ferrules crimped onto the ends of the wire which keep the copper from fraying and breaking.

I have connected many wires to screw terminals by "tinning" (applying solder to) the stripped ends of copper wire. Too much solder and you wind up with a rigid blob that doesn't secure well in the terminal, so one should apply just enough solder to keep the copper from fraying and separating.

If the connection generates enough heat to melt the solder, you will have bigger problems. In other words, don't worry about the use of solder versus ferrules.