Soldering Wires Together




When splicing wires together, it is important to get an electrical connection that will keep conducting even after your soldering iron has cooled off. Paramount to this is getting a good mechanical connection between the wires, not just an electrical one.

I was able to use TechShop's soldering stations and helping hands to keep everything in place while I worked.


Step 1: Prepare Your Wires

Freshly stripped multi-filament wires need some attention before they will take well to being soldered.

First, the filaments of each wire should be twisted together, or pigtailed, to keep them orderly and behave more like a single entity.

I prefer to add some soldering resin to the filaments at this point too. It really helps the solder flow when tinning the wires. If using flux core solder, this step isn't critical, but it still does help.

Step 2: Tin Your Wires

Tinning the wires (melting some solder into the filaments with your soldering iron) before joining them will make the next step of soldering of the splice much easier. It helps distribute the heat quickly, and the pieces require heat for a much shorter time, since you don't have to spread as much solder around later. This reduces the likelihood that you'll melt through the wire shielding near the splice, or damage nearby components if soldering to a circuit board or to a component itself.

You want even distribution of the solder between the filaments, but not so much that the solder starts to swallow the filaments. The top wire in the picture is just about right, but the bottom one has too much solder. Too much solder will make the wires quite stiff, and they still need to be fairly pliable for the next step.

Step 3: Mechanically Join Your Wires

In order to resist being pulled apart, the wires should be wrapped around each other before the soldering takes place. This will make it so that if the wires are pulled on it isn't the solder holding things together. Solder's primary function is conducting electricity, not gluing things together (though it certainly does help with that too).

Wrap one wire around the other, taking care to leave enough metal exposed above the sheath so the other wire can be wrapped around it in turn. The turns of the wrap should sit next to each other and not overlap. Keep your wraps tidy.

Unfortunately my second wrap got rather untidy. Hopefully you can learn from having a bad example to criticize.

Step 4: Solder the Splice Together

Now that the two tinned wires are wrapped around each other, we can re-apply the soldering iron and the solder from each wire will melt and mingle, forming a nice solid solder joint. It will be necessary to add a little more solder to really fill in the cracks and get a high strength, low resistance joint.



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    8 Discussions


    2 years ago

    This is a great tip. Thanks.


    2 years ago


    Have a very important question: can you solder the same way (as you mention above) for big wires that will transmit 220vAC? Is there a max voltage acceptable for tin soldering? If i solder two 220vAC wires together as above, will the electricity flowing through make the solder melt away?

    Thank you very much.

    2 replies

    Reply 2 years ago

    Hi Cristian,

    If the wires are properly sized for the current you need, then the solder will not get hot enough to melt. I'm guessing you're trying to use current from your wall outlets? You'll be using 12 or 14 gauge wire, depending on the amperage needed by your project.

    Wires inside power transformers for your home appliances are often soldered to the circuit board. The problem would be if your wires are too small for the current you use, they would get too hot. An example would be if you used a headphone wire to try to power your fridge. There would be too much electricity flowing through a small conductor and the whole length of the wire would get hot. The plastic insulation would be more likely to melt before than the solder, however.

    Stranded wire for higher voltages is much better when soldering larger wires. The solder will 'wick' into the strands and provide a much better electrical connection. There isn't much of a mechanical bond if you try to solder large solid copper wires together (thinking house wiring style wire here).

    PLEASE use a mechanical bond to connect large wires. Never rely on just solder to hold things together, especially when dealing with lethal currents. Home improvement stores will sell crimp-on style connectors that will let you splice 12 or 14 ga. wires together without soldering, or you can even use wire nuts used in house wiring. Combining soldering with one of these mechanical methods will yield the best electrical connection.

    Since I don't know exactly what you're doing I'll go ahead and say: It is against building code and EXTREMELY dangerous to splice cables inside a wall. It must be done in a junction box using appropriately sized wire nuts.

    Be sure to insulate your splices!


    Reply 2 years ago

    Thank you very much, this is exactly the answer i was looking for!

    I am building my own CNC and i need to solder some wires from my wall plug to multiple components that require 110vAC, and i wasn't sure if it would pose a resistance to the electricity flowing (thus melting the solder).


    Reply 3 years ago


    3 years ago

    Thanks for this! Useful for project!


    4 years ago on Step 4

    Cheers for this wee guide, just what I needed.