Tinning is a process of using a soldering iron to melt solder around a stranded electrical wire. The process of tinning wires before soldering is commonly used to hold the fine wires together, and it makes it easy to connect them to screw terminals or other connectors. This also ensures that all of the wires are making an electrical connection. A simple soldering gun can be used as a wire tinning tool, along with a pair of wire strippers.
Not all wires should be tinned, however. When determining when to tin or not to tin wires, consider whether the wire will be crimped. The solder joints of some tinned wires can break when crimped, so using a crimping tool or a ferrule on the wire may provide a more reliable electrical connection than tinning.
To tin electrical wire properly, you must use the right type of solder and follow a few basic tips and techniques.
How Tinning Stranded Wires Works
Note that there is no "tin" involved in tinning. The only material used is electrical-grade solder. When heat is applied with a soldering iron, the solder fills in the voids between the wire stands, creating one solid wire that can be easily bent and placed underneath terminal screws. This ensures a tight electrical connection and virtually eliminates the possibility of loose wire strands touching the junction box or coming out from beneath the terminal screw.
What Is Electrical-Grade Solder?
Electrical-grade solder typically has a rosin core that contains a material called flux, which helps to improve the electrical connection and strength. The other main type of core—acid-core solder—is used in plumbing but can damage electrical components.
Soldering must be performed with caution! The soldering iron gets very hot and can cause severe burns. Always place the soldering iron on a heat-resistant surface while it heats up and cools off. While soldering, always works above a heat-resistant surface and away from anything flammable. Be careful not to overheat the wire and melt the wire insulation. It's a good idea to practice soldering using scraps of the same wire you will solder for your project.
If you're working with an existing wire during an electrical project, it's also important to determine its type before tinning or connecting any new wires; you can tell if the wire is aluminum or tinned copper by cutting one end and closely inspecting the internal section.
Choosing the Right Solder
The best solder to use for tinning stranded copper wire is electrical-grade rosin-core solder. This is an acid-free solder that contains a flux in the core of the solder. Never use solder that contains acid to strip and tin wires, as this can damage the wire or its insulation. Acid-core solder is intended for use in plumbing applications. If you use a different type of acid-free solder without a rosin core, you may need to apply flux to the wire as part of the soldering process.
Equipment / Tools
- Soldering iron
- Stranded electrical wire
- Wire strippers
- Acid-free, rosin-core solder
Prepare the Wire
Tinning must be done on bare wire. If the wire is insulated, strip about 3/4 to 1 inch of insulation from the wire end, using wire strippers. This length gives you enough wire to wrap around screw terminals but not enough so that excess wire will be exposed.
Prepare the Soldering Iron
Plug in and turn on the soldering iron, and let it heat up. Quickly wipe the tip of the soldering iron on a damp sponge. This removes any oxidation that may have occurred while the iron was heating up.
Apply Solder to the Wire
Extend the solder from its spool in a straight line. If desired, you can clamp the wire in a "third hand" tool or similar heat-resistant holding device.
Touch the tip of the solder to the tip of the soldering iron to create a small pool of liquid solder on the iron's tip. This will help conduct heat to the wire. Then, touch the tip of the soldering iron to the bottom side of the wire so the solder pool is in contact with the wire.
Apply the solder to the top side of the wire, opposite the soldering iron's tip. The solder should melt and be drawn in around the wire strands. Move the solder and soldering iron together along the bare portion of the wire, melting the solder as you go. Especially when tinning a thin wire, touch the solder to the wire quickly to prevent the solder pool from becoming too thick.
Let the Wire Cool
Let the solder cool, then inspect the results. The solder should create a thin coating all the way around the wire and should not form a glob or heavy bead, which creates electrical resistance. Usually, the wire strands are visible under the solder.
If there is excess solder around the wire, heating it up again will liquefy it so it can be wiped away.
If desired, use needle-nose pliers to bend the tinned wire into a candy-cane-shaped hook that easily wraps around the screw terminal on devices such as switches and receptacles.