How to Solder Wires Together (Splice, Heat-Shrink and Tin)

Joining two wires with solder is one of the most useful skills in electronics, robotics and repair — and one beginners most often get wrong. The secret is not the soldering itself but the preparation. Get the prep right and the joint almost makes itself.

What you need

• A temperature-controlled iron at around 330–350°C
• Thin rosin-core solder
• Wire strippers and a pair of helping hands to hold both wires
• Heat-shrink tubing (and a heat source) or electrical tape

Step 1: Strip and tin each wire

Strip about 10–15 mm of insulation from each wire. For stranded wire, give the exposed strands a gentle twist to gather them.

Now tin each wire: heat the bare strands with your iron and feed in a little solder until the copper is coated in a thin, shiny layer. Tinning locks the strands together, removes oxidation and means the final joint comes together in seconds. Do not skip this step — it is what separates an easy splice from a fight.

Step 2: Join the wires mechanically

Solder conducts; it does not glue. A joint that is mechanically sound before you solder will always be stronger. Two common methods:

• Western Union (lineman’s) splice — lay the two tinned wires side by side pointing in opposite directions, then wrap each one tightly around the other. Strong and self-supporting, ideal for wires that will take strain.
• Hook joint — bend a small hook in each tinned wire, link them and crimp closed. Quicker, good for low-strain connections.

For a simple inline join, even just holding the two tinned ends firmly together works — but a splice is more reliable.

Step 3: Solder the joint

Bring your iron onto the joined wires and let them heat for a second or two, then feed in solder. Because both wires are already tinned, the solder will flow instantly and bond them. You want the solder to flow into the joint, leaving a smooth, shiny surface — not a lumpy blob sitting on top. Remove the iron and hold the wires still until the solder sets.

If the joint looks dull or grainy, you may have moved it while cooling — that is a cold joint, and you should reflow it.

Step 4: Insulate with heat-shrink

Bare solder joints must be insulated. The neat way is heat-shrink tubing:

1. Before soldering, slide a piece of heat-shrink onto one of the wires, well away from the heat.
2. Make and cool the joint.
3. Slide the tubing over the finished joint and apply heat (a heat gun, or carefully the side of your iron) until it shrinks tight.

Forgetting to thread the heat-shrink on first is the classic mistake — there is no way to add it once the joint is made, short of cutting and redoing it. Electrical tape works in a pinch but is bulkier and less durable.

Practise on something forgiving

Wire splicing is a skill that rewards repetition. Practise on offcuts before you commit to a real repair, and once your joints come out shiny and strong every time, you are ready for anything from a robot kit to a real-world cable fix. New to the iron entirely? Start with the beginner soldering guide.