Custom Cable & Design Considerations
Custom cables are extremely complicated, at least at first glance. Once you break down the different sections of the wire and the different options it becomes a much easier process. The first thing to keep in mind before choosing any of your materials is to fully understand what your custom cable will be subject too. Will your cable be surrounded by other cables, in a high-temperature environment or even be subject to contact with acidic chemicals?
Four custom cabling parts that could make or break your application:
Choosing the correct conductor is the first important consideration. An electrical conductor can come in tinned, nickel, silver, aluminum and bare copper. Although bare copper is typically the most used, each material type has unique characteristics that help applications in different ways.
1.1 Silver: is the most conductive, but also the most expensive. With the price so high there are only a few applications that can greatly benefit off this material.
1.2 Nickel: is a strong choice for operating at high and low temperature ranges. It also has the ability to continually operate in applications that are subject to environmental influences like acids, water and leaching.
1.3 Aluminum: conductors are known for their lightweight and cheap cost. Aluminum is also one of the least conductive materials, which is why conductors are typically much larger than any other type.
1.4 Copper: is the most used conductor, because of its low thermal expansion, cheap price and high conductivity.
1.5 Tinned: conductors are the easiest material to soldier, which makes custom cables and cable assemblies much easier to install. Has a moderate conducting ability.
Standing is a factor that is often overlooked, but is still important when creating custom cables. The different custom cable stranding are:
Bunch: When the conductors' strands are twisted together with no arrangement.
Concentric: is when a central wire is surrounded by another layer of wires and that layer is then surrounded by a following layer. Unlike other standing types once one layer is placed the following layer will often twist the opposite direction with six more wires than the previous layer.
Unilay: has its strands arranged in a circular pattern, with the different layers twisted in the same direction.
Rope lay: is a concentric lay and has groups of wires laid by on one another in order to form a rope type figure.
2. Insulation & Jacketing
The second major factor to consider when designing a complicated custom cable is the insulation and jacketing. Typically insulation and jackets are used as a protective outer layer against any incoming physical abuse like flexing and moisture. There are two major types of insulation and jackets Thermoplastic and Thermoset.
Insulation is the first layer, which is in direct contact with the conductor; therefore the primary job for cable insulation is to stop any leakage (current from escaping). Insulation is also designed to stop any incoming physical abuse the cable may face during its application. Some of the resistances that different types of cable are able to withstand are high and low temperatures, flames, moisture, chemicals and abrasion. The insulation also has to consider internal electrical considerations like capacitance, attenuation and voltage rating.
Jacketing is the outer layer of the custom cable and is designed to protect everything inside of it from chemical, moisture and mechanical damage. Jackets similar to insulation come in a range of customizable colours that makes for easy identification and grouping. Being the outer layer characteristics to consider are the flexibility, colour, high and low-temperature flexibility, flame resistance and shelf life per application.
Popular insulation and jacketing materials:
- PVC (Polyvinylchloride)
- PE (Polyethylene)
- PUR (Polyurethane)
- TPR/TPE (Thermoplastic rubber/elastomer)
- Thermoplastic CPE (Chlorinated Polyethylene)
- PO (Polyolefin)
Insulation and jacketing are responsible for not only protecting the cable from the outside; they also have to stop leakage from the inside. Custom cables typically won’t require shielding unless they’re designed for telecommunication applications or are in close proximity to a large number of cables. Shielding is mainly designed to protect against interference called EMI (Electromagnetic Interference). EMI can affect your application in a number of ways, but shielding has a number of ways to protect against it.
3.1 Spiral: Spiral shields often are created out of a number of different materials, but certain metals such as steel may be used for additional physical protection. Spiral shields typically have the highest flexibility and are easily manufactured with 65% overall coverage, while weighing less than most other spirals options.
3.2 Braid: The braided shield has moderate flexibility with the material interwoven into a tubular structure or a rectangular cross-section. The braided shield is the oldest form of shielding but is also one of the strongest and most reliable. These braids come in many different material types like steel, aluminum, tinned copper, silver plated copper & bare copper.
3.3 Foil: Foil shields appear in the shape of a foil gum wrapper and are almost always constructed with tape being either Mylar or Aluminum. Being typically constructed with a drain wire while providing 100% shielding, allows for more effective EMI and noise resistances.
3.4 Combination: This type of shielding is by combining 2 or more shields, which are then created into a single cable. The most common type of cables to combine is the braid over foil or braid over braid. The combination shield is typically used for its 100% foil coverage, mechanical strength, its physical protection, its low DC resistance and flexibility.
Fillers are relied on for a number of electrical cables, because of how they provide a rounder and smoother construction. Another important thing to note is electrical fillers help strengthen the cable, so when a cable is moved it can do so easily. Fillers lastly support the cables outer layers, while increasing the flexibility of the construction.
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