#0003: Basic techniques for connecting wires

Connections discussed:

1. Straight solder splice
2. Pig-tail splice
3. Western Union splice
4. T-junction splice

STRAIGHT SOLDER SPLICE

The straight solder connection is made by aligning two opposite facing wires in adjacent-parallel, tinning them individually, then soldering them together. This joint is most suited for smaller gauge wires. Especially in low-voltage or low-current applications.

I find I use this joint frequently when prototyping and stringing various PCB modules together, such as power-supplies and buck-boost converters. This is because it allows me to make a more than strong enough bond very quickly; and without damaging the wires, by avoiding subjecting them to repeated mechanical strain. For example: by twisting them together and soldering, then de-soldering and unravelling them whenever I want to disconnect a module; as is the case with the other types of joints. With this connection however, it is simple: align and solder to connect; then apply flux, heat, and pull apart to disconnect.

The straight solder connection is actually rather strong in my opinion. When applied properly, it creates a bond that can not be pulled apart easily. I tested this joint by wrapping the wires around my hands then trying to pull the joint apart. It might eventually give, but only after considerable force is applied.

Despite it’s initial success with my basic stress test; I still wouldn’t recommend using this type of joint for any permanent applications. This is because, in my opinion, I don’t believe that it will stand up well in most real-world settings. Settings that involve: temperature swings, vibration, or constant stress on the wire and joint. These things can exacerbate any small imperfections in the weld to the point that they can create fissures that can either cause problems like intermittent connections or outright brake the bond. Since the solder is the only thing keeping the connection, any stress applied to it isn’t mitigated by anything. This strain coupled with environmental heat would make this type of connection unreliable in the field. An example of this would be wiring around an engine.

Still though, as long as the wire is not subjected to any real or ongoing strain in its application, it is not a bad option to utilise this type of connection. Especially for temporary or semi-permanent add-ons to an already established system. For example adding a voltmeter module to an electric bicycle to keep track of the battery levels. That way the module can quickly be de-soldered off or be further modded later with a switch as an example. This type of bond also has the smallest footprint. Allowing smaller sized heat-shrink to be easily applied as insulation.

PIG-TAIL SPLICE

The pig-tail or rat-tail splice is probably the most common type of connection that I have encountered in the wild. It is made by holding two wires in adjacent-parallel (facing the same direction), then twisting the exposed ends together. Its a quick and dirty solution to make a good mechanical connection. Usually this type of connection is insulated with either sticky tape or even heat-shrink for a semi-permanent solution. It is not soldered in many cases, as the twists and tape tend to make a ‘good enough’ connection for the use-case.

The alignment of the connecting wires is something to take into consideration when deciding whether or not to use this splice. In cases where the wires are to remain adjacent-parallel and facing the same direction; the pig-tail splice is a good candidate. It will allow the user to join two wires next to each other, whilst minimising any change of location, necessary in order for the wires to accommodate the new connection. Example use-case: connecting 2 or more adjacent wires within a ribbon cable. Additionally, with this setup: the connection can be easily soldered and insulated with heat-shrink by sliding it over the open end.

However in cases where the user is joining two opposite facing wires, they are usually left with a connection made up of a twisted pair that veers off at a right angle. This is then folded onto one of the wires in order to apply insulation. This is mechanically weak, as it concentrates any stress on the wire/connection or more accurately “pulling force”; at the bend. The first twist where the two wires meet.

This configuration of the pig-tail splice rarely takes solder well without ending up with an overly large footprint or bulge that the user has to then slide heat-shrink over. It is also too easy to melt the wires whilst soldering because of how close the insulation on the wires are to each other.

To conclude, this connection is good in solder-less temporary or semi-permanent applications. But if you want a more permanent bond (especially for opposite facing wires), the western union splice is a far better solution.

WESTERN UNION SPLICE

The western union splice is named after the Western Union Telegraph Company. This connection involves crossing the exposed ends of two opposite facing wires together, at a mid-point between the wire’s exposed tip and the start of it’s insulation: in an “X” shape. Then twisting them around each other’s exposed base sections. Continue twisting until the insulation of the opposite wire is reached. Then trim off any excess exposed wire tips. This makes a linear and very strong mechanical connection between the two wires; by maximising the contact area the wires have with each other within the connection. It also functions as a knot of sorts, and once properly soldered, it becomes essentially stronger than either wire itself. In addition it has a relatively small footprint and consequently takes to sliding heat-shrink over it rather well.

This is probably my most favoured splice for permanent connections. However for those same reasons, it is also largely inappropriate for temporary applications. This is because it becomes a hassle to de-solder and untangle the wires. This process will also almost definitely damage the wires involved; by fraying and breaking some copper strands from the stress of unravelling.

THE T-JUNCTION SPLICE

The “T” junction splice is any connection where you add a third wire to an existing connection. The most basic version involves removing the insulation from the mid section of a wire; then wrapping another wire around the exposed section before soldering it in place. Then insulating it. This method can also apply to any of the above connections – and the strength of the additional connection usually depends on the strength of the underlying connection.

You could opt to pig-tail together three wires into a T-junction (or four into an “X”, etc…), or straight solder three wires, or even create a western union splice, then tightly hitch the third wire over that connection for maximum strength.

At its most basic a ‘T’ junction splice is exactly that. Three wires connected together in a rough ‘T’ shape. Everything else is up to the user, and largely depends on the use-case and it’s needs.

SOURCES / REFERENCES / FURTHER READING:

https://en.wikipedia.org/wiki/Western_Union_splice

https://en.wikipedia.org/wiki/T-splice

https://en.wikipedia.org/wiki/Rat-tail_splice

https://en.wikipedia.org/wiki/Point-to-point_construction

https://en.wikipedia.org/wiki/Printed_circuit_board

https://en.wikipedia.org/wiki/Solder

https://en.wikipedia.org/wiki/Flux_(metallurgy)https://en.wikipedia.org/wiki/Soldering