The ability of cryogenic seals to maintain integrity is often critical not just for the processes involved but for the safety of humans, other equipment, and the environment. Seal failure could lead to expensive damage, hefty lawsuits, and even loss of life. Finding reliable solutions that can handle cryogenic temperatures and the pressures involved is challenging but not impossible.
Canted Coil Springs for Latching, Holding, and Locking
Many associate canted coil springs with spring-energized seals, but they can be used for much more. For example, canted coil springs provide a lightweight, easy-to-install alternative to traditional mechanical fasteners.
Canted Coil Springs Fasteners
Canted coil springs can perform three different fastening tasks:
- Latch: fastens two parts together
- Lock: permanently fastens two parts together
- Hold: holds and aligns two parts together
Note that both holding and latching allow for the parts to be disconnected and reconnected. However, if two pieces are locked together, they cannot be separated without either damaging the canted coil spring or the connected parts. Also, note that canted coil springs can be used for quick-release locking, which allows the lock to be bypassed for a quick, simple release. And in all fastening applications, the force required to latch, lock, or hold can be specified by the engineer and accomplished by varying the coil space, wire diameter, spring width, and height.
Advantages of Using Canted Coil Springs as Fasteners
There are several benefits to using canted coil springs instead of more traditional mechanical fasteners. For example, they are easy to install and require no special tools, shortening assembly time. They are also highly reliable and provide dependable performance over thousands of insertion/removal cycles.
Canted coil spring fasteners experience almost no compression set and provide precise, predictable forces even when subject to a wide range of temperatures. Furthermore, the individual coils compensate for mating surface irregularities, misalignment, and dimensional variations.
Their lightweight, compact nature makes them ideal for use in applications where weight and available space are at a premium, and they can also reduce the complexity of assemblies. Finally, and perhaps most importantly, they can serve other functions besides fastening, such as grounding, service as multi-point conductors, and providing tunable EMI/RFI shielding.
Applications of Canted Coil Fasteners
In the medical industry, canted coil springs are used for both latching and holding in various applications, including implantable and non-implantable devices and surgical devices, such as customized tools for use by specific surgeons. An example of an implantable device would be joint replacements that require highly reliable locking.
The oil and gas industry depends on canted coil springs’ highly reliable mechanical fastening capabilities for advanced downhole tools where insertion and breakaway forces must be controllable. In the renewable energy market, canted coil springs work well as connectors within the highly confined environment of turbine nacelles.
The automotive and aerospace industries find them an ideal approach to fastening in applications where SWaP (Size, Weight, and Power) is critical. In addition, canted coil springs are regularly used in the defense industry, where specific applications include aircraft system connectors and optoelectronics connectors. Finally, canted coil springs also work well for underwater, fluidic, and satellite/orbital connectors.
Canted coil springs are a simple, reliable, multi-use alternative to traditional mechanical fasteners. Benefits include the ability to compensate for dimensional changes, lightweight and compact nature, and their ability to reduce the complexity of systems. They can also serve as not only fasteners but EMI shields and multi-point conductors. And keep in mind that their use ranges from medically implantable devices where their ability to respond to particular insertion/removal forces is critical as well as the harsh and dangerous world of downhole tools in the oil and gas industry.
FlexForce Canted Coil Springs
Advanced EMC’s FlexForce Canted Coil Springs are available in 300 Series Stainless Steel, Hastelloy, and copper alloys with gold, silver, or nickel plating. In addition to light, medium, and heavy load spring forces, the forces can be customized. Our FlexForce canted coil springs are available in wire diameters between 0.25 mm (0.010 inch) and 1.50 mm (0.059 inch) and coil widths between 1.5 mm (0.039 inch) and 15 mm (0.591 inch). However, other materials, finishes, and dimensions may be available.
Contact us at firstname.lastname@example.org or call us at (918)-994-7776 to learn more about the FlexForce canted coil springs and how they can benefit your designs.
Canted Coil Springs For Conduction
Flexforce Canted coil springs, can be used as effective electrical conductors. They can provide reliable current conduction despite challenges such as vibration, dynamic conditions, and shock loadings where other conductor solutions would fail.
Situations That Pose a Challenge for Conduction
Certain operating conditions can make it challenging to achieve a solid connection for conduction. For example, vibration and shock loadings, such as those experienced in downhole tools for the petrochemical industry, can cause more traditional electrical connections to eventually work loose and risk the integrity of signal and power transfer.
Any time there is a high probability of motion, such as EV/HEV battery pack connections, there is also a risk that the integrity of the electrical connection could be compromised. In the power industry, issues can arise with heat and reliability for high-current applications that perform conduction, grounding, and isolation.
Rotating parts, high temperatures, and variations in loadings are also challenging for maintaining electrical connections and common to wind energy applications involving turbines. In addition, rotating parts in robotic end grippers and similar automation equipment pose similar issues.
Implantable devices, such as neurotransmitters and pacemakers, require electrical connections that must also be highly reliable, lightweight, and compact. In addition, lightweight design approaches are critical for many applications, including unmanned vehicles that must be lightweight to maximize their battery-constrained range.
And some applications, such as semiconductor fabrication, need to take advantage of solutions that can perform multiple purposes, such as conduction combined with latching/holding/locking or EMI shielding.
Canted Coil Springs
Our Canted coil springs, also known as slanted or slanting coil springs, are often used as electrical conducting springs to achieve high integrity connections for applications such as those just described. However, several factors make these springs different, starting with their ability to maintain consistent force over a wide range of deflection.
The Individual coils that make up these springs maintain contact with the mating surface despite surface irregularities, misalignment, tolerance variations, and dimensional changes. In addition, they experience little to no compression set and are ideal for oddly shaped cross-sections.
When used as electrical conducting springs, the individual coils serve as multiple contact points for electrical conduction and grounding; essentially, each coil is a contact point. As long as one coil remains in contact with the surface, then the electrical connection is maintained.
Benefits of Canted Coil Springs for Conducting
There are numerous advantages over more traditional approaches when canted coil springs are used for electrical conduction. For example, canted coil springs can be designed to meet specific electrical requirements in addition to being manufactured from materials with high conductivity. Varying parameters such as spring diameter, wire diameter, coil height, canted angle, and the number of turns make it possible to tune amperage and electrical resistance for optimized solutions. In addition, platings such as gold or silver can be used to achieve ultra-low impedance.
Because of the extensive surface area of canted coil springs, they can transmit high power levels while generating less heat than traditional solutions. As a result, they provide outstanding heat-to-current carrying capacity even in extremely high temperatures. This same aspect is also essential in implantable devices where heat generation must be minimized for patient safety. In addition to their conducting capabilities, canted coil springs can serve as excellent EMI/RF shields for applications such as downhole tooling in oil exploration.
Canted coil springs support SWaP (space, weight, and power) requirements while reducing system complexity. This system simplification is often seen when they are used for mechanical fastening (latch, lock, or hold) in addition to electrical conduction. They make it possible to achieve far greater contact densities in smaller spaces than equivalent conductivity solutions. And one of the outstanding features of canted coil springs, as alluded to earlier, is their ability to provide specific force levels for fastening that include low force insertion.
As discussed in the previous section, these springs are able to maintain contact with surfaces despite factors such as impact and shock loadings, angular misalignment vibration, dimensional changes, and mating surface irregularities. In addition, they maintain performance in other harsh conditions by using materials and platings that are corrosion resistant. And canted coil springs, when designed and installed correctly, can reduce the possibility of conductor fatigue failure in relation to multiple insertion/removal cycles. Their minimal compression set also contributes to their extensive operational life.
Finally, canted coil springs are easy to clean and sanitize if needed for medical, pharmaceutical, food, and beverage applications.
Canted coil springs are used as highly reliable electrical conductors in industries such as medicine, transportation, aerospace, semiconductor fabrication, industrial, energy, and defense. From surgical bones saws to guided weaponry, canted coil springs have provided dependable, effective conductivity solutions.
Advanced EMC FlexForce Canted Coil Springs
For economical, reliable, SWaP-friendly conductivity solutions, Advanced EMC FlexForce canted coil springs may be the answer. The experts here at Advanced EMC can help you determine if a canted coil spring conductor will meet your design specifications and constraints. And if it does prove to be what you need, they will be there every step of the way until you have the conductor your design requires.
To learn more, you can also read 7 Things to Know About FlexForce Canted Coil Springs.
Canted Coil Springs for EMI/RF Shielding
Canted coil springs are an effective, reliable solution for some of the toughest EMI/RF shielding challenges. But what makes them different from other options, like wire mesh over polymer and finger springs?
What Are Canted Coil Springs?
Sensitive electronics need protection against EMI (Electromagnetic Interference) , RF (Radio Frequency), and crosstalk, and they need to avoid interfering with other electronics. Among the EMI/RF shields on the market are canted coil springs. These springs get their name from the angle at which the individual coils are set. This allows them to achieve a consistent, highly predictable force once installed, which makes them ideal for latching, locking, and holding as well as spring-energized seals. As just mentioned, they also provide highly reliable EMI/RF shielding made possible in part because each coil serves as a contact point for conduction or grounding.
Where Canted Coil Springs Are Used for EMI/RF Shielding
Canted coil springs are used in a variety of applications where they provide shielding for data and signal transfer, including
- Antenna bases
- Power management systems
- Electronic enclosures
- Waveguide flanges
- Connect/disconnect assemblies
- Coaxial and electrical connectors
Whenever EMI/RF shielding is involved, there are critical national and international standards that must be complied with. These standards come from several different organizations, including the following:
- CISPR (Comité International Spécial des Perturbations Radio), dealing with emission and immunity as well as test methods and the equipment used for testing
- IEC 61000 (International Electrotechnical Commission) focusing on EMC (Electromagnetic Compatibility)
- ISO (International Organization for Standardization) standards specifically for automotive EMC concerns and covers road vehicles, earthmoving equipment, and forestry and agricultural machines
- SAE (Society of Automotive Engineers) EMC Standards Committee
- EN (European Norm) standards concerning unwanted electrical emissions and immunity to unwanted electrical emissions
- FCC Part 15 (Federal Communications Commission) for unlicensed radio-frequency transmissions
- MIL-STD 461, 464, and 469 (Military Standard)
For a product to be sold on either the national or international market, it must be in compliance with relevant standards. To learn more about canted coils, click this link to read the most common questions about canted coil springs.
Benefits of Canted Coil Springs for EMI/RF Shielding
There are several advantages to using canted coil springs for EMI/EF shielding, starting with their ability to serve two or more different purposes in a single design.
Multipurpose Mechanical and Electrical Solution
Canted coil springs can be used for multiple purposes in a single application: they also perform latching, holding, and locking functions. They do so with highly predictable forces and almost no compression set. When they are designed correctly, these springs can provide precise insertion and breakaway forces. Canted coil springs perform these mechanical functions without the use of tools and can significantly simplify a design when used as a multipurpose solution (i.e., latching and EMI shielding).
Lightweight and Flexible
Canted coil springs are extremely lightweight and compact, which can make them an excellent option for SWaP (Size, Weight, and Power) constrained applications. Their flexibility allows them to be used with many geometries other than circular that would be otherwise challenging to shield.
Standard spring wire is available in wire diameters from 0.25 mm (0.010 inches) to 1.50 mm (0.059 inches). Standard coil widths range from 1.5 mm (0.039 inches) to 15 mm (0.591 inches). However, there are custom options available for wire diameter and coil width. The angle at which the coils are oriented can also be specified. Finally, the coil pitch can be varied, and is usually quite dense for EMI/RF applications.
Material and Plating Options
There are several different material and plating combinations available for canted coil springs. The most commonly used spring materials include …
- Stainless steel
- Beryllium copper
- Zirconium copper
- Platinum iridium.
These materials can be combined with platings such as nickel, silver, gold, and tin. Platings are especially useful when the springs may be exposed to corrosive environmental conditions.
While canted coil springs already work across a very broad spectrum of EMI interference, they can also be tuned to very specific impedance specifications. This can aid not only in device performance but in achieving compatibility with the appropriate EMC/RF standards.
Because canted coil springs can provide a near-constant force, they will remain in contact with surfaces extremely well. This is true even when subject to vibration, shock, and impact loads as well as dimensional changes due to temperature fluctuations. Canted coil springs do an excellent job of compensating for hardware variations, surface irregularities, and angular misalignment, leading to highly reliable performance even in difficult operating conditions.
If you are looking for an economical, effective, and reliable EMI/RF shielding solution, consider the use of canted coil springs. And the experts here at Advanced EMC can help you choose the right spring options, tune it to the impedance you need, and ensure that your design will comply with the right standards. Contact us today to learn more about our Flex-Force canted coil springs.
Most Common Questions about Canted Coil Springs
Here are answers to seven of the most common questions asked about canted coil springs.
Where Are Canted Coil Springs Used?
Canted coil springs can be used in many different ways, but many are not aware of exactly how versatile they are. In the medical industry, they are used to shield equipment from crosstalk that could compromise the integrity of data. The automotive industry depends on canted coil springs to achieve solid mechanical and electrical connections while reducing weight and minimizing the complexity of assemblies.
In the oil and gas industry, they are used to achieve both electrical and mechanical connections in the rugged environment of downhole tools. Canted coil springs protect sensitive equipment from lightning strikes in the aerospace industry. And those are just a few examples of how they can be used.
What is a Canted Coil Spring?
Traditional springs have all the coils perpendicular to their longitudinal axis. Canted coil springs, on the other hand, have the individual coils parallel to each other and at an angle to the longitudinal axis. Because of how the coils are oriented, these springs can effectively serve a wide range of uses that traditional springs cannot.
Are There Any Other Names for a Canted Coil Spring?
Yes, as a matter of face there are. Canted coil springs are also called slant coil springs and cant coil springs, both in reference to the angle (or cant) at which the coils are parallel to each other.
What Makes a Canted Coil Spring Special?
Because of the cant of the coils, these springs have a flat load curve when compressed–which is rather unusual for a spring. This means that the load generated as these springs are compressed is predictable through their wide deflection range.
What Can Canted Coil Springs be Used For?
Canted coil springs have four specific areas of application in which they excel: energizers for spring-energized seals, mechanical connectors, multi-point electrical connectors, and EMI/RF shielding.
Canted coil springs are one of the options when specifying a spring-energized seal. Spring-energized seals provide outstanding performance in spite of issues such as uneven mating surface, hardware gaps, runout, eccentricity, out of roundness, and seal lip wear.
In that context of spring-energized seals, canted coil springs generate a flat load curve that in turn keeps friction at a predictable, constant level. This is extremely important in sealing applications for which friction and torque are critical to the functionality of a seal. In addition, canted coils do not experience compression set. Canted coil spring energizers work best when there are moderate to high speeds involved and are ideal for situations where friction needs to be highly controlled.
First, canted coil springs work well for latching, or fastening two parts together so they can still be disconnected when needed. They also work extremely well at locking, where two parts are permanently “locked” together. Holding is another task for which canted coil springs excel: two parts can be aligned and retained, but with sliding possible. Sliding is highly controlled by spring force generated when the canted coil spring is deformed.
In this type of application, canted coil springs can be fine tuned to achieve highly specific insertion and removal forces. This is made possible by the nearly constant spring force that these springs generate over their deformation range.
One of the more interesting applications of canted coil springs is their ability to provide EMI/RF shielding. Their electrical properties can be adjusted to meet specific impedance requirements to achieve optimal shielding for certain ranges of interference, including both conductive and radiated. And they work extremely well at shielding from crosstalk.
These springs can easily adapt to even the most uneven and irregular shapes, allowing them to provide a consistent level of shielding, and can be used with connect/disconnect assemblies, waveguide flanges, rectangular electronics enclosures, and both radial and coax connectors.
Multi-point Electrical Conductors
Canted coil springs can also serve as multi-point electrical conductors. Because surface area provided by the canted coils, they provide a cooler operating temperature which can be critical in certain designs, including those where space is highly limited. Canted coil springs can serve as both conductors and grounds, in both static and dynamic applications. Their multi-point contact system means they can keep electrical contact even in extremely harsh conditions, including those where vibration and shock are common.
What Kind of Materials Are Canted Coil Springs Available In?
The three most common materials for canted coil springs are:
- 300 Series Stainless Steel (e.g., 316, 316L, 302)
- Copper alloys
In addition, they can be nickel, silver, or gold plated if needed.
If there is going to be extremely high temperatures and/or exposure to corrosive media, Elgiloy is typically recommended. For shielding or use as a multi-point conductor, stainless steel and copper alloys work extremely well.
What Kind of Options Are Available for Canted Coil Springs?
The basic options for canted coil springs outside of those related to materials are …
- Wire diameter
- Coil size (width and height)
- Coil cant angle
- Number of independent coils
- Inner and outer diameter of the spring
By adjusting these parameters and material selection, specific performance goals can be achieved.
Canted coil springs are useful in so many different applications, and their performance is fully proven in the field. Whether you need highly reliable spring-energized seals for use in vacuum conditions, locking components for orthopedic implants, a way to protect rectangular electronics enclosure from a specific range of interference, or a multipoint conductor that also serves as a latching connector, canted coil springs are an excellent option.
And remember that Advanced EMC offers FlexForceTM canted coil springs. Our engineers can work with you to find the right combination of characteristics and properties to meet the needs of your application. Contact us today!
7 Things to Know About FlexForce Canted Coil Springs
FlexForce canted coil springs have special characteristics that make them useful in a variety of applications, ranging from locking components together in an orthopaedic implant to providing an energizer for mission critical aerospace applicants. In this blog post, we will introduce seven key facts about FlexForce canted coil springs that you need to know.
Are a Specific Design for Springs
Canted coil springs, also known as slant coil or cant coil springs, are springs that have the individual coils set at an angle to each other, rather than having them all parallel. This coil configuration significantly impacts the performance of these springs and makes them ideal for a wide range of uses.
What makes canted coil springs different from other types is the fact that they have a flat load curve when they are compressed. Because of this, canted coil springs generate predictable loads throughout their wide deflection range.
Can be Used as Mechanical Connectors
Canted coil springs are ideal for applications that involve latching, locking, or holding to connect two components (also known as detent mechanisms). Latching involves fastening two parts together so that they can still be disconnected when needed. Locking creates a permanent connection that can only be broken by damaging the sea. Holding, on the other hand, both retains and aligns parts and makes sliding possible via the controlled spring force.
Canted coils are commonly used to connect two mating surfaces in a highly predictable, repeatable fashion thanks to the flat load curve. When canted coil springs are used, the insertion/removal force can be engineered to a high degree of accuracy. And when used as a latching, locking, or holding connector, FlexForce canted coil springs provide a lightweight, high strength option that can be used for practically an infinite number of cycles.
Can Provide Exceptional EMI/RF Shielding
One of the common uses of canted coil springs is their ability to effectively provide EMI/RF shielding. Furthermore, the electrical properties of these springs can be customized to provide more optimal shielding against certain ranges of conductive and radiated interference.
Add to this the fact that they can adapt to irregular and uneven shapes to provide consistent shielding, and it is easy to see why they are a common choice for applications that need to be protected from harmful electromagnetic and radio frequency crosstalk interference.
Can Act as a Multiple Point Electrical Conductor
Some designs depend on multiple electrical contact points, which a canted coil can provide. Using a canted coil spring for electrical connections results in a reliable connection that results in a cooler operation temperature. It allows engineers to manage more power in compact spaces and provides both conducting and grounding capabilities in both static and dynamic applications. In addition, canted coil springs as electrical conductors can perform in some of the harshest operating environments that may involve vibration and shock. It should come as no surprise that canted coil conductors are often used in medical applications inside the human body.
Can be Used with Spring Energized Seals
Canted coil springs work extremely well as the energizer in spring-energized seals. Because of the energizer, spring energized seals are able to maintain contact with the sealing surface, even if issues such as out of roundness, uneven mating surface, runout, hardware gaps, eccentricity, or seal lip wear are present.
The flat load curve of these springs also means that friction stays fairly consistent in dynamic sealing applications. This makes them ideal for sealing situations that involve critical friction and torque specifications. In addition, canted coil springs are very unlikely to experience compression set.
Available With a Range of Options
There are several options for canted coil springs. They are available in varying levels of spring force: light, medium, and heavy. And canted coil springs come in both standard and custom sizes. As to the spring wire itself, they are available in wire diameters between 0.25 mm (0.010 inches) and 1.50 mm (0.059 inches). As to the coil width, they come in sizes ranging from 1.5 mm (0.039 inches) and 15 mm (0.591 inches). However, designs can be highly customized if needed.
Finally, the three most common wire materials are Hastelloy, stainless steel (usually 300 series), and copper alloys. For use as a conductor or EMI/RF shielding, stainless steel is recommended. For applications that involve high heat and corrosive media, Hastelloy and Elgiloy may be recommended. Also keep in mind that these canted coil springs can be obtained with nickel, silver, or gold plating.
Used in a Wide Range of Industries and Applications
Canted coil springs are being used in a diverse group of industries and applications, including oil & gas, renewable energy, aerospace, defense, fluid power, transportation, semiconductor manufacturing, and medical devices.
- As a mechanical connector, canted coil springs are often used to lock together frame assembly of a ventilator cart or to hold components together in wind turbines.
- As a multiple contact point conductor, canted coil spring assemblies are often used in active implantables such as pacemakers or neurotransmitters.
- As EMI/RF shielding, canted coil springs can be found in electrical enclosures or used with data transmission cables.
- As a part of a spring energized seal, canted coil springs are used in critical aerospace applications and dangerous petrochemical environments involving extreme heat and corrosive materials.
FlexForce canted coil springs can be used as detent mechanisms, EMI/RF shields, multipoint electrical conductors, and energizing springs in seals. They are available in a number of options and can be fully customized to meet user needs. In addition, their reliable performance has already been proven in number industries and applications. If you are interested in FlexForce canted coil springs, contact us at Advanced EMC today.
How Canted Coils Springs are Used in Medical Applications
There are several distinct benefits to be had from using canted coil springs in place of more traditional springs. Because of this, it should come as no surprise that these springs are used extensively in medical applications.
Canted Coil Springs Are Effective Electrical Connectors and Contacts
Canted coil springs are being used more and more for electrical contacts and connectors. Canted coil connectors make it easier to replace leads and lead segments without harming the patient, and lead interface solutions based on canted coil springs can significantly reduce risk to the patient. In some applications, the procedure time and the patient’s recovery time can be reduced through the wise application of canted coil springs. Canted coil springs also provide high contact power density with a minimal amount of temperature rise. In many instances, they can also reduce the size of the medical device and provide multi-channel connections.
Canted Coil Springs Can Provide EMI and RF Shielding
Another benefit of canted coil springs is their ability to provide shielding from harmful EMI and RFI interference in applications such as ultrasound equipment and vital signs monitors. Many times the medical data being transmitted cannot afford a compromise in its integrity of the disruption of the data flow. Canted coil springs can actually be tuned to meet specific impedance specifications so that medical equipment and devices can be protected from dangerous crosstalk interference.
Canted Coil Springs Can Be Used in Spring-Energized Seals
Canted coil springs can be used in spring-energized seals in medical equipment and external devices as well as implantable devices. Spring-energized seals are often used to maintain a seal when there are problems with hardware gaps, runout, eccentric contact surfaces, and vacuum pressures. In short, spring-energized seals can provide an effective seal where other seals would fail, and when canted coil springs are used then a far more consistent spring force can be applied.
Canted Coil Springs Serve as Reliable Mechanical Connectors
Canted coil springs can provide a reliable connector in three specific ways:
- Holding and retaining two parts in alignment with customized forces, often used for surgical instrumentation
- Securely fastening two parts together while allowing them to still be unlatched (where the latching force can be customized), which is also being used with surgical instrumentation
- Permanently locking two parts together, including use during orthopedic implant surgery
Unlike most mechanical connector solutions, canted coil springs can achieve these connections with strength, reliability, and incredibly high precision. In addition, when canted coil springs are used as mechanical connectors, there is an option to customize the forces for insertion and breakaway.
Medical Applications of Canted Coil Springs
There are a host of specific medical applications where canted coil springs have proven invaluable. The following is just a sampling:
- Cochlear implants
- Implantable medication pumps
- Insulin delivery systems
- Orthopedic instruments
- High-speed surgical power tools
- Ultrasound equipment
- Pain management devices
- Vital signs monitors
- Hemodialysis equipment
- Cardiac rhythm management devices
Canted coil springs are used in connection with everything from neurostimulators to orthopedic implant surgery. Their ability to serve as electrical connectors/contacts, shield from EMI and RF interferences, serve as the energizer in spring-energized seals, and provide tailored mechanical connections make them ideal solutions for many different medical devices and implantables.
Canted Coil Springs: Benefits for Medical Applications
What is a Canted Coil Spring?
Canted coil springs (also known as cant or slant coil springs) are not your typical spring, and this becomes obvious when you take a look at the three different types of tasks they support:
- Acting as a mechanical connector
- Energizing seals for better performance
- Providing EMI/RFI shielding
- Serving as a multiple contact point conductor