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A wire ferrule is a copper plated tin tube that slides over the stripped end of a stranded wire. It is available in both insulated and non-insulated versions. The insulated wire ferrule contains a nylon extruded jacket intended to reduce signal leakage, creepage and reduce gas intrusion. The nylon jacks are color-coded by wire AWG (American Wire Gauge) or the Cross-Sectional Area of the conductor in millimeters squared (mm²). The color code will either follow the Industry Standard, which is commonly found throughout North America, or the DIN Standard (German Institute for Standardization) commonly found throughout Europe.
There are many benefits to using wire ferrules that far outweigh the minor cost per piece and additional labor and tools required to install them. Below is a list and explanation of the more common benefits, to help you make an educated and informed decision before using or omitting them.
- Stray Strands. The most common stated benefit is the reduction of stray strands. The outer insulation jacket holds the strands of multi-stranded wire together. Removal of this jacket, required to terminate the wire, allows the strands to separate. A stray strand can be hard to see and can cause electrical shorts resulting in system failure, or even arc flash. Due to the natural funnel design of wire ferrules, strands are less likely to separate as they are installed into the ferrule. Any strands that separate while getting installed into the ferrule are easier identified while holding the wire in hand in optimal lighting, as opposed to trying to check for any stray strands after the wire has been landed in a terminal, which often times can be hard to see. Once the wire ferrule is properly crimped onto the stripped end of the wire, the strands will no longer be able to separate. This reduces the amount of caution the user must take with each conductor while routing and handling the wire prior to landing.
- Repeated Re-termination. In applications where wires must be inserted and removed numerous times, stranded wire quickly breaks down and can become a tangled mess. The installer will be faced with the option of cutting the wire shorter to restore a sufficient wire end (which is not always possible), or landing the wire and suffering from a degraded, unreliable, and potentially dangerous termination point. A wire ferrule on the end of the wire allows for repeated insertion and removal, without degrading the end of the wire.
- Connection Failure. - Weidmuller a manufacturer of electronic components, including ferrules created an excellent whitepaper on the benefits of wire ferrules, and how they can prevent connection failure. Through their study, Weidmuller documents the long-term electrical performance of connections, using Solid Wire, Stranded Wire, and Stranded Wire with wire ferrules by measuring the change in contact resistance in salty and standard environments over time. Weidmuller reports that Stranded Wire while being more resistant to vibration, and having superior flexibility and flex life, degrades much faster. Depending on the environment the connection of bare stranded wire can fail within two to four years. In contrast, a stranded wire with a wire ferrule can provide a connection that can demonstrate resistance over time that compares to a solid wire.
In summary, for a minor cost, wire ferrules can provide all the benefits of solid wire in addition to the benefits of stranded wire, allowing you to gain the advantages of both options. Beyond understanding the importance and benefit of using wire ferrules, make sure the builders at your Contract Manufacturer and Panel Shop have been trained in using the proper tools and have defined best practices for selecting, installing and verifying the proper application of wire ferrules.