Conductor Stranding: Poor designs lead to breakage.

Conductor stranding is an important component for applications with hi flex cycles or vibration. The higher the conductor stranding the better the resistance to stress caused by flexing. Custom cables with high strand count conductors are the best choice for these types of applications. Higher conductor stranding also makes for an ultra flexible wire when using the right insulation. Discussing the flex requirements with your wire and cable manufacturer is critical to choosing the right cable construction.

Are there circumstances when conductor stranding doesn't help with wire breakage and loss of conductivity? Yes! Recently, I was asked what type of wire I would recommend for an application that required the wire to be soldered onto a PCB. This person was repairing PCBs experiencing conductor breakage at the solder point due to vibration and he thought the wire was to blame. This is a common problem when the wire is soldered onto PC boards especially now with the use of lead free solders.  Applications such as aerospace that are subject to vibration and movement of the wire can cause stress at the solder point.  The problem has nothing to do with conductor stranding or flexibility of a wire, while it is true that high strand conductors and the use of alloy materials adds strength to the conductors. The reason for this has nothing to do with the conductor stranding or how flexible a wire is, but the termination. Termination with connectors is recommended to solve this problem. Cable assembly and contract manufacturers understand this problem and are using edge cards and other types of connectors for termination with newer PCB applications. The problem is more prevalent among legacy boards that are being repaired where retrofitting connectors is usually not an option. Often times a strain relief cannot be installed due to the nature of the application. The solution to repair this type of problem with the old boards may be as simple as using an epoxy to secure the wire to the board to prevent stress at the termination point.

Having the right strain relief is important especially with handheld devices. The lack of or using the wrong type of strain relief can actually cause a stress point and product failure. Strain reliefs can vary in sizes and materials, consult your cable assembly house or contract manufacturer for guidance. I had a customer experiencing conductor breakage on his handheld tool and sent us a sample for analysis. Though his design used high strand count conductor strands, we found the conductor stranding to be damaged at the strain relief, it was discovered the strain relief design had been changed to a spring which caused added strain to the conductors. He changed his design and the returns on his product ceased.

The moral to the story is that though high stranded conductors do resist the stresses of flexing, the cause of the problem may not be in the cable design. Take the time to consult your cable manufacturer and the contract manufacturer for the best material options for your device.

Reverse Engineering: Why you need it and when.

Do you need a wire or cable and have no idea what it is? You are not alone, it happens more times than not especially for equipment repairs, obsolete parts, and failure analysis. When do you need to have a cable reversed engineered? You may like a particular cable's performance or you have a piece of cable that you or your customer may want more of but don't know what it is or who manufactured it. Then reverse engineering is the answer. Who performs this service? Most custom wire and cable manufacturers can assist you.

Reverse engineering wire or cable is commonly performed to determine:

• Conductor stranding and material.
• Cable construction
• Insulation and jacket materials

Custom wire and cable manufacturers routinely reverse engineer wire and cable to identify the materials used and the cable construction. It is best to provide a sample between 1 to 2 feet if possible and keep in mind it will be dissected in the process.

Outer jacket
Reverse engineering wire and cable begins with measuring the outside diameter (OD) of the wire or cable. The longer the piece the better it is to obtain the nominal OD. The outer jacket is carefully removed to expose the core. Normally, cross sections are taken of the outer jacket to measure wall thickness. Jacket material is tested to identify the type of material used.

Braid, shield or tape
If there is a braid or shield the construction will be examined. The pitch, number of ends, material and coverage can be determined at this point. If there is a tape wrap present, the overlap, type of material and size will be examined.

Core construction
The next step is to examine the cabling construction. Once the shield and/or tape is removed the following can be determined: Cable lay or twists per inch, filler material used, the use of strength members, number of conductors and conductor color code.

Conductors
The conductor material, plating used (if any), gauge and conductor strand count and construction are checked. A cross section of the conductor will identify the wall thickness of the insulation and OD. At this point the insulation material will be identified.

Insulation and jacket materials
There are several ways to identify the materials used for insulation and jackets. The obvious is the look and feel of the insulation or cable jacket. Computer analysis and burn testing are also used. Plastics and rubber each have distinct characteristics when placed on a flame. Experienced engineers can determine the type of insulation material by whether it burns, melts, or self extinguishes. The odors produced when burned also are distinct to each type of material. Burn testing should only be done by experienced individuals in a controlled environment, gases can be toxic as well as the risk of fire is present.

Failure analysis
Failure analysis is another reason for reverse engineering wire and cable. When a cable fails, determining the cause can many times be done with reverse engineering to pinpoint the problem. Common problems with handheld devices with poor strain relief is damage to conductors or conductor stranding due to excessive bending. Shielding materials can over time damage conductor insulation. Dissecting the cable at the problem area can expose the problem. Custom wire and cable manufacturers can make material suggestions such as the use of higher conductor stranding or alloys, insulation materials or cable construction design alterations based on the findings of reverse engineering.

Super Flexible Wire Designs: High strand count conductors

A super flexible wire design requires two things, a flexible insulation material and the right conductor stranding. Even with the most flexible wire insulation, the flexibility of the wire will depend on the conductor stranding. Conductor construction is key in achieving a noodle like flexible wire. There are two things to look at when choosing the right conductor:

1. Number of strands. Conductors are made of many fine strands which are cabled together to meet the required gauge size. Conductor stranding is available from one strand (solid) to hundreds depending on the gauge size. The higher the strand count the more flexible and resistant to flexing fatigue the wire will be. For example a 24AWG wire the stranding options are from 1 strand (solid) all the way to 105 strands. That’s quite a range.

2. Conductor construction. How these fine strands are put together is as important as the strand count. The most common configuration is concentric. Concentric conductor may be defined as: a central wire (strand) surrounded by one or more layers of helically laid wires in a geometric pattern. Rope stranding has the advantage of increasing flexibility by using a larger number of finer strands while maintaining a tighter diameter tolerance than a simple bunched construction.

Flexing vs. Flexibility

High Strand Silicone Wire

To some flexibility means to withstand repetitive flexing, while to others it means how much the wire will bend and rigidity. For both types of applications a high stranded conductor is recommended. For repetitive flexing one should consider using an alloy material for higher strength and flex cycles. For noodle like flexibility a standard copper conductor is fine.

Flexible cables

Flexible cables also use high strand conductors, but there are more factors involved controlling the flexibility; Such as, Shielding, outer jacket material, cable lay construction and type of conductors just to name a few.

It's always best to discuss your flexibility needs and the conductors available with a wire and cable manufacturer, especially one that works with high strand count conductors. Off the shelf (commodity) wire manufacturers usually work with solid, 7 and 19 strand conductors which are less flexible than the high strand conductors.

Conductor Stranding: How important is it?

Conductor stranding can be a bit confusing. Wire and cable is manufactured in a variety of configurations, not all wire is the same. The conductors for wire (aside from solid core) are made of multiple strands of fine wire bunched or twisted together. Conductor stranding plays an important part of the flexibility and the performance life of the wire. The more individual wire strands in a wire, the more flexible, break-resistant and stronger the wire is. Hi flex applications where repetitive flexing is required use different stranding than wire used to wire a building or home. "Off the shelf wire normally is available in solid, 7 strand and 19 strand constructions which is fine for applications not requiring flexibility or repetitive movement.

Repetitive flexing can cause conductor strands to break over time which lowers the conductivity of the wire. Using higher strand wire helps eliminate this problem. High strand wire is used in medical handheld devices, robotics and even headphones.

Many custom wire and cable manufacturers offer high strand wire which you cannot obtain easily from distribution. For example, a 20AWG wire can be manufactured with a solid conductor or solid core all the way to 168 strands. Knowing which conductor stranding option will best suit your needs is important.

Identifying the conductor call out: A typical call out is XX (YY / ZZ). The "X" is the gauge of the wire, "Y" is the number of strands and "Z" is the gauge size of those strands. Once you understand what these numbers mean, identifying the conductor construction is simple. A wire gauge chart is a handy tool to view wire gauge stranding options

The more common conductor stranding configurations are concentric (true concentric, equilay concentric, unidirectional concentric, and unilay concentric), bunched and rope.

Rope stranding is conductor construction consisting of single strands assembled together into concentric or bunched configurations. Rope constructions consist of concentric or bunched members stranded together into the final concentric or bunched configuration. Rope stranding has the advantage of increasing flexibility by using a larger number of finer strands while maintaining a tighter diameter tolerance than a simple bunched construction. Ropes are more evident in the larger AWG sizes, such as 8 AWG and larger, but there are also many applications that require the flexibility of rope constructions in the smaller gauges. Constructions vary and can contain hundreds or thousands of strands.

Depending on the use, the type of conductor is important. Hi flex and load bearing applications would require conductors with higher tensile strength such as alloys. Copper conductors are normally for less rigorous flexing

Flexible wire is a term which can be interpreted in many ways from hi flex to the actual flexibility of the wire. Letting your cable manufacturer know what your expectation is for the flexibility of your wire or cable will help in choosing the right conductor stranding. Calmont has manufactured extremely flexible large gauge wire and cable as big as 4/0 which is limp and flops over the end of a table. Of course insulation and jacket material also plays an important role in making a flexible cable, but the conductor stranding is where you start

Custom Cable-High Performance Custom Wire and Cable

What makes a wire or cable a custom wire or cable? One would think it would have to be an elaborate cable design, but in reality something as simple as a unique color or printing can make the cable become a custom cable.

Custom wire and cable is not readily available or stocked by distributors or manufacturers. Simply put, custom wire and cable is anything that is made to order specifically for a customer. Hypothetically, let's say you have a commodity cable that you use regularly but now your product design has changed and you need one or two more conductors. You check with your distributor and the manufacture doesn't offer that construction. You now need to turn to a custom wire and cable manufacturer which is set up to run special construction cable with little or no minimums

.Yes you will pay a little higher per foot than you do with the commodity wire however, you get exactly what you need and the performance you require. Prices between custom and commodity cable can't be compared as the construction and materials are different and the quantity produced are much lower with the custom cable. In the end it's all about having choices available to make a better product.

A few benefits of using custom wire and cable include:

• Engineered specifically for your application
  
• Custom configurations
• Custom colors and/or printing
• Improved performance

You have choices! When having a custom wire or cable designed you a wide range of options to assist in building the right wire or cable for your needs. Some options include:

• Gauge sizes, smaller gauges available
• Insulation and jacket materials
• Type of shielding and construction
• 
  Conductor stranding, plating and type
  

Reverse engineering is used in situations where the origin of a cable is unknown or there is no information about the wire or cable. Engineers in most cases will carefully dissect the wire or cable taking measurements and noting the construction of conductors, cable lay, shielding, fillers and other vital information. A series of tests are performed to determine the insulation and jacket materials. At this point if a customer would like to see improvements in the cable's performance such as a more flexible cable, or higher flex life it should be mentioned to the engineers so changes can be made to the design.

So who uses custom cables? Just about every industry including medical, robotics, aerospace, music/audio, and more. Building a better mousetrap often means designing a product that will exceed its expected performance and the wire and cable needs to be considered as well.

If you do not know much about wire and cable properties, don't be alarmed. Custom cable manufacturers have engineering resources to assist you with every step of the way starting with deermining the right materials and construction based on your application and requirements.

If you have questions about custom wire and cable or a project that you need assistance with, contact Calmont for assistance. Feel free to post any questions or comments you may have. If you enjoyed this article please feel free to share it.