A detailed comparison of wire splicing methods


Splicing is an important part of custom cable assembly, and there are several methods by which splicing can be performed. Each is different, and understanding their pros and cons can help you design your cable and properly outfit your assembly team.

In this article, we’ve detailed the most common methods for wire splicing and introduced a new method that could prove an effective alternative for you or your custom cable supplier. Three of the most common splices are:

  • Solder splice 
  • Butt splice 
  • Heat shrink splice 

Let’s talk about them in order of least effective to most effective, and then we’ll get into the details of an alternative option: the machine-splice.

Heat shrink splice

A heat shrink splice is performed by inserting the wires into either end of a cylindrical heat shrink sleeve that contains a ring of solder. When you heat the sleeve up with a heat gun, the solder liquifies and binds the wires while the sleeve tightens to seal the area of the connection. It’s a simple splice to perform and requires minimal equipment and labor beyond preparing the wires.

While soldered splices are generally considered more reliable than crimped splices, not all soldered connections are created equal. The quality of connection achieved by a trained expert with a soldering iron isn’t consistently achievable at scale with a heat gun and shrink splice connectors. You just don’t have enough control over the solder as an operator. For this reason, we never use this method ourselves and don’t recommend it for production.

However, since all that’s needed is the connector itself and a heat gun, it can be a preferred method for field maintenance when a soldering iron is unavailable. If you’re considering using heat shrink splices for your production line due to their ease, bear in mind the potential cost of product failure.

Butt splice

A butt splice connector looks like the heat shrink connector, but it is a crimp connector rather than relying on heated solder. The connector piece contains a metal ring, which connects to each end of wire you plan to splice.

All you have to do is insert your prepped wire into each end of the butt splice and crimp with a hand tool. The connection is sealed by crimping the connector around the wire individually, and the ring within the connector carries current between both cables. Once the connection has been crimped, heat shrink tubing is used to create a seal.

The butt splice is the most common crimp connector, and it is relatively reliable. From a labor standpoint, it is more cost-effective than soldering but still requires manual effort and hand tooling to perform.

Solder splice

Soldering is the most common method for wire splicing in custom cable production, and it is the most reliable. The wires in question are connected manually (people have different methods, many twist the wires around each other like a “lineman’s splice”), and solder is heated with a soldering iron until it liquifies to fill and envelop the connection. Then, a sleeve of heat shrink is applied to seal.

While soldering provides the most secure connection for your splice, it is by far the most labor-intensive method. Its efficacy also relies on your ability to hire and train technicians effectively, as the skill level required is greater than any other method.

There are a number of mistakes that could be made when soldering a splice. One is to not get your solder hot and fluid enough, resulting in a “cold solder,” which provides a brittle, unreliable connection. Another problem occurs if too much heat is applied too liberally, which can damage the cable’s insulation. If the conductors aren’t well-connected before soldering you could end up with a dry solder prone to inconsistent connectivity.

A well-trained team member, however, should be able to avoid these issues and produce reliable connections consistently. The trustworthiness and durability of a soldered splice is reflected by its necessity in cases when cable is held to military or aerospace certification specifications.

The SAS 2-40 autosplice machine

Machine splice

If there’s a “best-kept-secret” of wire splicing, it is auto-splice machinery. But it shouldn’t be a secret and can be an incredibly valuable tool. Machine-splicing is nearly as reliable as soldering in terms of connection integrity and far more efficient.

In truth, a big reason we do most of our splicing via the soldering method is that manufacturers and engineers are generally unfamiliar with auto-splice equipment and are more comfortable with the status quo.

The auto-splice machine performs a crimp connection with a spool of brass-coated copper, which it cuts into a blank, stamps and forms a crimp around the wires. Then, heat-shrink can be used to cover the splice and provide the seal. The machine’s operator has full control of the machine’s motor with a foot-pedal and can process far greater throughput than with a soldering iron. Just like with any other method, wire will need to be cut, stripped and cleaned prior in order to perform the best splice.

a completed auto-splice crimp
A completed auto-splice crimp

Auto-splice machines are capable of performing wire-to-wire splices as well as wire-to-board splices and are useful for almost any connection, so long as the cables themselves aren’t too large. At around 14-gauge or bigger, the auto-splice is no longer reliable, and you’ll have to get the soldering iron out. In any case where a butt splice is used, an auto-splice machine could take its place to save money and production time without sacrificing quality.

Just like with soldering, there are things that could go wrong if the operator isn’t careful. It’s important to make sure all the strands of a wire are set in the machine’s carriage before the splice is made, otherwise any loose strands will be left out of the connection. It’s important for you to be sure you’re using the proper die with the machine for each different size wire you splice. Otherwise, connections will either be too tight or too loose to be reliable. The auto-splice is far simpler than the soldering iron to learn and provides some relief on that front to manufacturers struggling with staffing and training.

All things considered, auto-splice machinery is a slightly less reliable but far more cost-effective splicing method than soldering. With the right quality-control measures in place, using an auto-splice machine could make tons of sense for your facility or for your suppliers. Plenty of custom cable specialists will use auto-splice machinery, but it is worth making sure your supplier has the tooling available, especially if you want to produce at scale.

Still have questions?

Hopefully this article can serve as a helpful guide, but we know nothing beats talking with an expert. If you have any questions about wire splicing, tooling or designing connections for manufacturability, please reach out.

We love talking shop and would be excited to hear about what you’re working on.