Circular Plastic Connector Basics Many contact styles are available for CPC connectors. The different designs address current carrying requirements, size requirements, termination methods and cost. -- ECN , 3/1/2002 Circular plastic connectors (CPCs) were developed in the 1970s as a rugged, low-cost connector to provide power input and output to and from virtually any device. They are generally regarded as an industrial power I/O connector. Today, while there are many connectors suitable for power I/O applications, the CPC continues to be the connector style of preference for many industrial designers. Designers have a large number of designs to select from when they specify circular connectors because there are many brands and styles available. Complicating the selection is the lack of widespread industry standards governing circular plastic connectors. Therefore, no two brands of CPC connectors are intermateable. Since brands are not intermateable, designers must look ahead when specifying CPCs to see what future needs are possible and determine if the current connectors will work in the future. One important attribute different brand CPCs share, however, is shell size designation. The majority of CPC brands have adopted shell size designations measured in 16ths of an inch. For example, a connector with a shell size of 11 is 11/16". Additionally, many CPC suppliers design backward compatible products so that a connector designed 25 years ago can mate with a connector designed two years ago. Why Circular? CPCs provide designers with more efficient use of real estate compared to square or rectangular designs. It is easier to fit more connector pins into a circular pattern than into a square or rectangle. Why Would a Designer Pick a CPC Over Other Connector Types? For the most part, it comes down to ruggedness. There are several possible alternatives to CPC for industrial power I/O applications, but they often fall short because the plastics are not robust enough or the contact systems are not suited for an industrial environment. Do not blame the connector for this apparent shortcoming. Many of the alternatives to a CPC were designed for high-volume applications in either light industrial or commercial products. In those applications, the connectors were not subjected to many of the rigors CPCs were designed to handle (dropping, shock, dragging, fluids, dust and other abuse). CPCs are usually available as a free-hanging or flanged housing version. There are designs for printed circuit board mounted versions, too. Typically, a free hanging CPC is used to connect cable assemblies. These cable assemblies are frequently exposed to potential abuse — personnel traffic, moving equipment such as forklifts and other sources of physical abuse. They may also be exposed to environmental conditions such as rain, salt spray, oils and other fluids. On the other hand, free hanging CPCs may be enclosed in wiring cabinets or other protected enclosures. CPCs with a flanged housing connect to a panel cutout or bulkhead. This type of connector is fastened to the bulkhead with screws. They too are subject to the same application and environmental conditions, but they do not have the "slack" which may exist in a cable-to-cable free hanging application. Consequently, flange mounted CPCs may encounter more abrupt physical shock abuse. For instance, if a technician is working in the proximity of a flanged CPC, it is conceivable that an errant blow from a hammer or slipped tool may impact the connector housing. This type of handling is normally not a problem for a CPC connector, but other consumer/commercial "soft" connector styles may break, deform or require replacement. In most CPC applications, designers are handling current in three basic ranges. The bulk of the applications are up to 13 A. Some applications extend to 20 A and finally, there are some CPC applications that require 50 A or higher service. If a designer has a connector need in these ranges, chances are not only is the application a candidate for a CPC, but there probably is an off-the-shelf CPC to meet the requirements. The next consideration a designer is faced with is the pin count for the connector. Typically, most CPC applications use a connector with between four and 37 positions (assuming a size 16 contact). There are several other designs, though. Among the others are connectors with up to 63 pins (using the smaller, size 20 contacts), special power contact connectors and various power/signal hybrids. This decision is specific to the application. The objective is to select a connector with an appropriate number of contact positions. The designer should look at how much current is going through the connector and refer to any current carrying capacity guidelines. Also, the designer should consider how future demands would affect the connector and the cost. In some situations, it may be advisable to select two small connectors compared to one large connector. The footprint and profile of the connector and how it fits into the design weigh heavily on the selection process. It is conceivable to use a larger position size than the immediate need specifies to allow for future additional positions to be used in the same connector. What About the Connector Housings? CPCs employ a number of housing configurations. Popular housing sizes are the 11-4 (11/16", four position) and the 13-9 (13/16", nine position) shell sizes. The majority of configurations involve circuits of 13 A or less. These applications use an industry standard size 16 contact and accommodate housings with four through 37 positions. If the application requires a maximum of 7.5 A, the designer can move to a smaller contact (size 20), and use housings with higher pin counts (typically a minimum of eight positions and a maximum of 63 positions). As power requirements increase, designers may employ 25 A contacts and use housings with anywhere from three to seven contacts. Other popular housing configurations include combination power/signal, high current (up to 50 A), high-current combination, and metal shell CPCs (called CMC) for the ultimate in rugged circulars. As far as housing materials, there is really only one game in town. The material of choice for these connectors is UL 94V-0 stabilized, heat resistant thermoplastic. This material offers the best mix of desirable properties at reasonable cost. For example, the material is relatively lightweight and exhibits the heat resistance and thermal shock properties necessary for high current applications. The physical shock resistance of this material is probably the most desirable property. What Types of Contacts Should Designers Use? For the majority of applications (13 A or less, free hanging or panel mount), stamped and formed contacts are the most common. These contacts are size 16 crimp style contacts and mate as a pin and socket. Multiple wire sizes, from 14 through 30 AWG, can be used with this contact style. Solderable contacts are available for field repair. For board mount applications in the 13 A or less range, posted contacts with solder compatible tails are normally used. Contacts in this range are sometimes called "signal" contacts although they do carry power. Current-carrying capacity will be less for board mount applications. PC board mount versions are available in all the different contact sizes and configurations. Some special contacts and upgrade programs allow designers to work with currents up to 17 A and beyond. In these applications, either a precision screw machined contact is selected or a contact insert upgrade like a Louvertac band is used. Precision screw machined contacts may handle up to 17 A. Louvertac bands, which are installed in a screw machined contact socket or around a screw machined pin, provide multiple points of contact and increase the mated surface between the pin and socket. The combination of a screw machined contact with a Louvertac band allows designers to reach up to 23 A. By using Louvertac bands with screw- machined contacts, contact resistance may be reduced, and the contact can handle increased current. Dedicated power contacts, on the other hand, are generally larger and more robust to handle the increased current flow and resulting heat. In this category, there are some fundamental contact design changes. Screw machined contacts are used, but to obtain higher current flows, a formed high-current male/female contact may be used. This contact type changes the mechanics of the entire connector. Rather than circular holes inside the connector housing, these contacts command a square opening. The male portion is a blade and the female component is a slot. Depending on the contact finish, these crimp contacts may handle up to 35 A. New contact technology for high power applications include scaled up versions of the screw machined contact with Louvertac bands. The screw-machined contacts are outfitted with square adapters so they can fit into the square holes in the connector housing. This type of contact may handle up to 60 A. A more economical contact for high power applications would be a round stamped and formed contact. This type of contact is smaller than the male/female contact mentioned earlier and reverts to a round pin and socket design. Applications up to 50 A could use this contact style. It provides designers with a product more suitable for high-speed production since they are usually available on a reel and can use automatic termination equipment. The per-piece cost of this stamped and formed contact is usually less than a screw- machined contact. What's Next? Once the housing and contacts are selected, most of the battle is over. However, accessories and options can be added to CPC connectors. Designers, depending on the application they are working on, may need the connector to be sealed. This decision depends on the type and degree of sealing required. For example, should the connector be sealed from solid foreign objects such as dirt, dust or other materials? Alternatively, is it more important that the connector seal out splashes of water or temporary immersion in other fluids? CPC connectors may employ wire seals or interface seals where connector halves come together. Additionally, designers can choose from one-piece seal designs or select two-piece seal designs. Other options to consider are cable clamp strain reliefs, right angle cable clamps, back shell extenders and panel mount flanges. Designers can use keying plugs to provide keying capabilities on CPCs. In applications where the wires need protection, some lines of CPCs can accommodate a flexible cable protection device. Flexible cable protection usually involves a flexible conduit of plastic construction which mates to the connector housing and provides increased physical, sealed protection of the wires and connector. Contact Materials and Platings Most stamped and formed size 16 contacts are constructed of brass. The brass materials have better "spring" properties than conventional copper contacts and allow the contacts to endure many mating cycles without diminishing contact performance. The contact finish for the brass size 16 contacts is usually tin-lead, but gold over nickel is also used. Screw machined contacts often use copper alloys with silver plating. The Louvertac bands used in conjunction with the screw machined contacts employ beryllium copper base materials and may employ either silver or gold platings. Solderable contacts revert to copper alloy base materials with tin or gold platings. Stamped and formed high-current contacts use copper base materials with tin-lead or gold plating. Assembling the Connector The first step in assembling a CPC (for a wire to wire application) is either crimping or soldering the contact to the wire. The majority of applications will involve crimping a stamped and formed contact to wire. The selection of the proper tool to perform this function involves looking at how many contacts will be terminated and how quickly they need to be terminated. For very low volume production or prototype applications, a simple ratchet style, manual hand tool can be used. As production rates increase, low-cost air powered tools are available. There is no rule of thumb on the level of tooling required other than looking at a total applied cost for each application. In medium to high-volume production applications, semi-automatic bench-top machines are available to terminate contacts to wire. For maximum production rates, fully automated lead makers are available to cut, strip and terminate single leads. Most of the semi-automatic and fully automatic machines can be outfitted with equipment to monitor crimp quality. Applications for CPCs are extensive. They are used for power I/O on refrigerated trailers, locomotives, industrial control systems and other applications. The selection and application of CPC connectors is not a one-step process. By understanding the basic concept of why one should use a CPC and what the capabilities of CPC connectors are, designers can make informed decisions when specifying industrial power I/O connectors. Each application of a CPC is unique, so designers need to carefully examine the application and determine the specific requirements. Pin counts, current capacity, housing styles and environmental conditions all affect the final selection. Understanding what is available in CPC connectors will help designers make a proper connector selection. About the author: Greg Paukert is CPC product manager at Tyco Electronics, Box 3608 MS 38-41; Harrisburg, PA 17105- 3608; (717) 985-2220; firstname.lastname@example.org; http://www.tycoelectronics.com/.