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Wire ferrules are a convenient way to improve your wire connections. The ferrule (small bracelet) is hollow metal tube into which exposed wire is crimped. The crimped ferrule holds the individual strands in place providing a clean installation that minimizes the problems associated with stray wires. Ferrules are available for single wire or wire pairs. The twin ferrule is the topic of this post.
In many situations, twin ferrules can save you time, improve the look of your project, minimize resources, and increase troubleshooting speed. An example of the finished product is shown here on the Arduino Opta Programmable Logic Controller (PLC).
The twin ferrules are easy to spot when compared to the single wire ferrules. Instead of the round plastic insulation we see an oblong opening that will accepts two wires.
The Twin wires allow the designer to daisy chain connections. To better understand, consider this wire diagram showing the output connections on the Arduino Opta PLC. Observe that the green highlighted wire provides power to the left-hand side of each of the Opta’s output relays. For example, the daisy chain wire provides 24 VDC to terminal pin #5. When the O3 (output #3) relay closes, power is then supplied to the alarm claxon.
How to Perform the Crimp
The twin ferrules are easy to use.
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Cut the wires. The tool featured in this post is a combination wire cutter and stripper.
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Strip to an appropriate length. Here the term appropriate implies that the wires are slightly protruding from the end of the ferrule. Stated another way, there is wire along the entire length of the ferrule.
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Install the ferrule. There is no need to twist the wires. Simply hold the wires together and push till they are all the way inserted.
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Crimp the ferrule using a specialized crimp tool.
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Install the wire into your device such as the PLC shown in the opening picture.
Precautions
While the twin ferrule is convenient, it is not a universal building method. Here are a few guidelines for your consideration:
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The use of the daisy chain is limited to low power connections. High current can cause localized heating of the terminal or excessive voltage drop across the chain. For example, the Arduino Opta’s relays have a design maximum of 10 A each. The daisy chain with 20 AWG wire is woefully inadequate for heavy loads. This is mitigated by including a 5 A circuit breaker in the schematic.
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High current connections should have a dedicated wire leading back to a robust distribution block or an independent circuit breaker or fuse.
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A broken or loose connection can bring down portions or even the entire chain depending upon where the defect is located. This may be undesirable in certain situations, especially as related to safety. Be sure to consider panel construction practices as part of your Safety Integrity Level (SIL) analysis.
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Each ferrule is designed to accommodate a specific wire gauge. We must ensure that wire, ferrule, crimp, and end product connector all match. For example, do not substitute a twin ferrule for a single. The crimp may not hold the wire securely. The resulting high resistance connection may lead to localized heating at the terminal. Such a condition may be identified using a thermographic inspection.
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Use a quality crimp tool to prevent wire damage and provide a solid low-resistance connection.
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Don’t get carried away. The daisy chain makes sense only up to a certain point. Always consider the future repairs and modifications to the system. It may be better to run a new wire back to the distribution block.
When operated within their design limits dual wire ferrules can simplify your industrial control panel. Use them within the guidelines outlined in this post to retain the integrity and reliability of your project.
Best Wishes,
APDahlen
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