Custom Cable & Wire Design- 5 Myths of Custom Cable

There are many misconceptions when it comes to the subject of custom made cables. Many designers shy away from using custom cables due to not knowing what is involved or they have dealt with manufacturers who do not specialize in custom cable designs. Here are five myths that we can clear up.

1. Really expensive - People that are new to designing products often think you need thousands of dollars to have a custom cable made. The truth is for as little as $500 (sometimes less) you can have custom wire or cable made to your specifications. When comparing custom wire and cable to the "off the shelf" custom is obviously more expensive, but we are not comparing apples to apples here. Custom cable is designed to your specific product or application requirements which may require special materials or construction. In the early stages of product development where small prototype quantities are needed, the cost of the cable can be higher than production quantities.

2. Huge minimums - Using a custom wire and cable manufacturer is important. Custom cable manufacturers are set up to run many types of materials and constructions and usually have to set up the machinery for each job. Minimums are small or non existent. Commodity/ off the shelf manufacturers normally are running the same materials and construction over and over, so for this type of manufacturer to stop production to make an unusual cable is costly. If you approach a commodity manufacture, it is not uncommon to be quoted a 10k-15k minimum. Unless you are using an unusual or uncommon material that itself has a minimum buy, you can order small quantities from the custom cable manufacturers.

3. Expensive tooling charges - Custom cables do not normally do not require special tooling. Tooling charges or N.R.E. can be expected for custom printing, unusual shapes and flat ribbon cables which require special dies to maintain wire pitch and extruded shape.

4. Long lead times - Custom cable lead times can vary depending on material availability and construction. On the average hook up wire can have a 2-4 week turn around and cables can run 3-6 weeks. Commodity cable manufacturer lead times for custom cable can run 8-14 weeks or longer.

5. "I need to know all about wire & cable" - Design engineers sometimes shy away from custom cable designs because wire and cable is not their forte. Custom cable manufacturers have engineers and custom wire and cable designers on hand to assist their customers with choosing the right materials and construction. It's like having a wire and cable expert on your team. Cable designs are usually at no additional cost.

Of course there are exceptions to the statements listed above. Lead times and minimums can be affected by material choices and complicated cable designs. When considering custom wire and cable designs for your product, be sure to contact a custom cable manufacturer. Working with a company which manufactures custom cable products enables you to buy smaller quantities, faster turnaround, and you buy a cable specifically made for your application.

Medical cables and sterilization

Medical cables are manufactured using a variety of materials. Reusable medical cables often times are subjected to sterilization processes and are built to endure extended cycles of sterilization. Understanding how a wire or cable will be sterilized is crucial to determine what materials to specify when designing a medical device. Insulation and jacket materials vary when it comes to resistance to chemicals, heat and other sterilization techniques.

Common types of sterilization include:

• Heat/steam - Autoclave
• Chemical
• Irradiation - E-Beam & Gamma Ray

Autoclave (heat/steam) resistant materials for reusable medical cables include FEP®, TPE, silicone or with TPR or silicone rubber jackets. Radiation resistant medical cables can be made with silicone and Teflon® (if water is not present). TPE and PVC can be made for Gamma sterilization with limited sterilization cycles. PVC is not commonly used with chemical sterilization, alcohol based liquids can break down the plasticizers (an additive for PVC) and can make the PVC brittle and damage the insulation or jacket. PVC is more commonly used with disposable applications.

It is always best to discuss with your custom cable manufacturer what types of sterilization and how many sterilization cycles the cable will be subjected to. Cable manufacturers experienced with medical cables and their applications can help narrow down your choices based on sterilization techniques, bio-compatibility and other requirements.

Silicone Insulated Wire- Medical Grade Silicone Applications

Silicone insulated wire and cable is an excellent choice for medical cable applications. Besides being extremely flexible, silicone rubber can withstand autoclave and other forms of sterilization. Properties that make silicone suitable for medical applications include: Low thermal conductivity, low chemical reactivity, low toxicity and thermal stability (consistency of properties over a wide temperature range of 100°C to 250°C). Abrasion resistance is a concern when considering silicone insulation or jacket. Formulas for higher tear strength are available to increase resistance to abrasion.

Applications suitable for silicone cables include:

• Arthroscopic
• Surgical Robotics
• Electrosurgical
• Implantable
• Ophthalmic
• Foot Switch
• Patient Monitoring

What makes a material medical grade? Materials are tested for bio-compatibility and are categorized to be used for medical applications. Medical grade materials are generally grouped into three categories: non implantable, short term implantable and long-term implantable. Materials approved as USP Class V and VI can be considered medical grade, most medical grade silicone is at least Class VI certified.

Uses for medical grade silicone cables include:

• Tubing/Lumen
• Drains
• Feeding tubes
• Catheters
• Implants for long and short term use
• Sensors

Co-extruded and multi-layer silicone cables can be used for high voltage applications such as X-Ray and MRI equipment which require electrical noise suppression and limited power loss . Co-extrusion involves extruding a semi-conductive silicone layer around the conductor to remove air thus reducing corona. Extruding both semi-conductive layer and jacket simultaneously insures no air or particles are caught between the layers. Benefits for co-extruded silicone include corona, moisture & ozone resistance, lightweight and flexible cable design and radiation resistance to name a few.

When working with your custom cable manufacturer, it is crucial to provided them as much information as possible about the application, the environment, sterilization and bio-compatibility requirements. The more information you can provide to your silicone cable manufacturer will help in determining if silicone is right for your application and to offer you material choices that will enhance your product's performance.

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.

Silicone Cable- 5 Things you didn't know about Silicone Wire

Silicone wire is extremely flexible and resistant to high temperatures, everyone knows that. There are some misconceptions regarding silicone wire and silicone cables. Listed below are five facts you probably didn't know about silicone insulated wire that I get asked frequently.

1. It doesn't have to be tacky. Recently at a trade show I handed a visitor a sample of our silicone wire and he said: "Wow, this isn't sticky, we stay away from silicone because it's always sticky." Silicone rubber is normally tacky, this can be a problem especially in medical applications where you don't want dirt sticking to the cable. Silicone cables can be made so they are not tacky or sticky. This is accomplished with manufacturing techniques and formulas can be used to make the jacket smooth and not tacky. Normally silicone wire and cable is coated with Mica to keep it from sticking to itself during the manufacturing process, this coating is not acceptable in some applications that requiring clean environments. The alternative is to manufacture the silicone so it is not sticky from the start.

2. Available in ribbon cables. Silicone cables can be manufactured as ribbon cable a few different ways. Silicone ribbon cables can be extruded, bonded and even molded into ribbon and flat cables. Silicone ribbon cables can be extruded as a ribbon cable which offers the tightest center to center tolerances. Bonding the ribbon cable involves extruding the individual silicone wires separately then they are bonded together, this method is less expensive than extruding the ribbon cable because there isn't any additional tooling. Bonded silicone ribbon cables work best with IDC connectors and soldering. Molded ribbon cables are usually silicone wires encapsulated with a silicone outer jacket, this method allows for unique flat shapes.

3. Low outgassing formulas are available. Aerospace, specifically space applications often have outgassing restrictions for the wire and cable. Recent advancements with silicone formulas and manufacturing techniques have created low outgassing silicone cable. For space craft and satellite applications Calmont manufactures silicone wire and cable products which meet NASA .01% TML requirement. Depending on your outgassing requirements, check with your silicone cable manufacturer to find out what is available. Click here to view Aerospace insulation properties chart.

4. Reinforced silicone is available. High strength silicone formulas are now being used to increase abrasion resistance of silicone wire and cable. Fluorosilicone has better abrasion resistance than the standard silicone. Additional measures can be taken to reduce abrasion such as strength members between layers and nylon outer braid to protect the silicone insulation.

5. Doesn't burn. Silicone insulation is self extinguishing, it will not burn. Flame retardant additives can be added to meet flame requirements such as VF1

Medical Cables Choosing the Right Materials for Medical Cables

Medical cables are manufactured in a variety of materials. Knowing which type of medical grade insulation or jacket material to choose from medical cable manufacturers is important. Before designing a cable, you need to answer these basic questions:

• Is the cable disposable or reusable?
• Will there be patient contact? Bio-compatibility requirements?
• Will the cable be sterilized? If so how?

§ Flexibility requirements?

§ How will the cable be used?

Medical cables fall into two categories, reusable and disposable. Disposable one patient use cables are normally made of less expensive material such as PVC and are not subject to repetitive sterilization due to short term use. Reusable cables often times have to withstand many cycles of sterilization such as, autoclave, gamma, E-Beam, and chemical sterilization. Knowing how the cable will be sterilized is important in order to narrow down your jacket options as some materials will break down or can’t withstand certain types of sterilization.

Medical grade insulation and jacket materials differ depending on the type of contact it will have with the patient. Implantable grade insulation materials are usually Teflon or silicone rubber. Common jackets are silicone rubber or implant grade Polyurethanes. For other uses medical grade materials include PVC, TPE, polyethylene, FEP, PFA, and polyurethane.

Medical cables application and use vary from sensors to complex surgical devices. Relaying this information to your cable manufacturer is important. Cables can be subjected to repetitive flexing, abrasion, getting stepped on or rolled over by carts. Choosing a material that can withstand the day to day use will prolong the life of the cable.

The aerospace industry has applications which can be very critical of weight

The aerospace industry has applications which can be very critical of weight; Such as, missiles, rockets and satellites. When looking for ways to cut down equipment, payload, or satellite weight, the cable can be the last thing considered. One way to accomplish weight reduction in aerospace cables is to use metal clad aramid fibers for the shield and braid material instead of the standard copper. Aracon® is one such material which provides exceptional EMI shielding, strength and flexibility. Typically Aracon® fibers can reduce weight 60% in the braid, an overall reduction in cable weight of 26% on the average. Aracon® is combined with DuPont Kevlar® to provide high tensile strength and excellent conductivity. The large number of fine threads and the tendency of yarn to flatten and spread give this material more shielding coverage than copper. In the first photo you can see the amount of fibers on the end of the braid

Benefits for switching from copper braid to Aracon include:

• Overall cable weight reduction
• Added flexibility
• Increased strength
• Withstands repetitive flexing
• Improved EMI shielding coverage

Aracon® fibers are manufactured by only one company Micro-coax Inc. The Aracon® braid can be purchased either with the braid only (sock) or having the braid manufactured onto cables by cable manufacturers such as Calmont Wire & Cable. Calmont has had great success manufacturing cables using Aracon® for the space and military related applications.

The cost of using this type of material is considerably more expensive than the standard copper braid. The cost savings for applications such as satellites where weight savings equate to rocket fuel cost, definitely makes it a value. Depending on your shielding requirements, Aracon® is available with several metallic coatings, thickness and fiber sizes to meet your resistance needs. Consult your cable manufacturer or Micro-Coax for options available to you.

If you would like to learn more about EMI shielding, Aracon® or similar materials contact Calmont today. Your comments are welcome and if you find this article useful, please share it.

ARACON® is a registered trademark of Micro-Coax, Inc. KEVLAR® is a registered trademark of E.I. du Pont de Nemours and Company

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