In situations where a stranded copper wire needs to be secured around a screw terminal, a technique used by professional or skilled DIYers is to tin the stranded wire to make it easier to handle. For example, the wire leads on light fixtures or lamps very often consist of tiny stranded copper wires bunched together inside the insulating jacket of the wire. Tinning the tips of the stranded wires involves soldering them together so that the now-solid wire can more easily and securely fasten to a screw terminal.
This is the way professionals ensure that wire strands don't fray and separate when the screw terminal is tightened down over the wire.
The Tinning Process
Note that there is no "tin" involved in tinning. By using a soldering iron to add rosin-core solder to the wire strands, the solder fills in the voids between the wire stands and causes the loose, fine wires to become one solid wire that can be easily bent and placed underneath the terminal screws. This ensures a tight connection and virtually eliminates the possibility of loose strands touching the junction box or coming out from beneath the terminal screw.
Soldering should be performed with caution! The soldering iron gets very hot and can cause severe burns. Always place soldering iron on a heat-resistant surface while it heats up and cools off. While soldering, be sure to work above a heat-resistant surface and away from anything flammable.
Only rosin-core solder should be used. It has been called the electrical solder because it is acid-free, unlike acid-core solder that will corrode the wire strands. A smaller-style solder that is easy to feed and easy to melt is the best choice. Here's how to tin stranded wire:
- When using the soldering iron, first let the solder iron heat up until the solder will melt easily you test by touching it to the tip of the iron. Once the solder starts to melt, the soldering iron is ready to tin your wire.
- Now, hold the hot solder iron to the bare stranded wires with some force until the wire gets hot. Touch the solder to the wire, not the iron, to see when the wire is hot enough to start melting the solder. If the wire is not hot enough, the solder won't melt in and around the wire strands. Keep heating until it the solder flows with ease, gelling the wires together.
- Be careful! Don't get the wire so hot that the insulating jacket melts. You should practice on a spare piece of wire to get the hang of soldering. It usually works best to strip between 3/4" and 1" of wire insulation when performing this task. The idea is to have enough wire to turn around the terminal screw without excess wire hanging out.
- After tinning the wire, use long-nosed pliers to bend the tinned wire into a candy-cane-shaped hook that easily wraps around the screw terminal on devices like switches and receptacles. Be sure that the solder joint is evenly distributed and the connection is even and secure under the terminal. If tinning is being used to connect a wire termination, such as that associated with knob-and-tube wire connections, be sure that the connection point allows ample room for a wire connector over the joint and that there are no burrs.
The next time you have to work on stranded wires, like those in a lamp cord, remember this simple, little quick tip: simply get out your soldering iron, some rosin-core solder, and let the tinning begin.