Edited by Robert Repas
• Rectangular connectors overcome many of the problems associated with existing cylindrical connectors.
• Good grounding may boil down to be a connector issue.
Outdoor Push-Pull I/O Connector,
A Better Way To Keep Paint Out, machinedesign.com/article/a-better-way-to-keep-paint-out-0511
Live events usually need unique cable setups, no matter if the venue is a concert tour, festival, sporting event, sound stage, or movie set. And many events rely on rental equipment and services, which make cable layouts and connections problematic from the start. Product engineers, manufacturers, technicians, and professional sound engineers don’t need the added aggravation of troubleshooting connection problems given the demands of live events. Not surprisingly, similar problems beset cable and connector assemblies in many industrial applications such as machinery, automation, telecommunications, transportation, and energy.
The installation team for a live event usually assembles cable runs from standard lengths of trunk cable. Typical trunk cables may carry audio, video, control signals, and ac or dc electrical power. In some instances, trunk cables carry both signal and power inside one external sheath. These trunk cables can have fan-outs with multiple connectors for the various signals, which means dozens if not hundreds of mated connections are needed in each run. Historically, these composite cables have used multipin circular connectors that could produce a number of problems when mating cable segments.
Cylindrical connector designs vary, but the ones most widely used have threaded shells. While these legacy connectors typically use a key and slot design, their mating is not foolproof. The twisting motion on the connector shells while threading the two halves together can put torque on the pins before the pin housing key fully engages its mating slot. This often results in bent or broken pins and connection failures. The greater the number of pins, the more likely it is to occur. A large pin count typically means small-diameter pins to keep the connector size manageable. Just threading the connector shells together can take precious time depending on the environment and work conditions — and time is usually at a premium during live-event setups.
Another common irritant that consumes time is dealing with dented or deformed rings or threaded shells on cylindrical connectors. Similarly, threaded shells are vulnerable to connection difficulties due to cross threading. Or there may be dirt and corrosion in the threads. So with screw-type circular connectors you’re not always sure the contacts are completely engaged, and troubleshooting connection failures can be difficult.
Once damaged, small pins can be difficult to repair or replace in the field. Even crimp style pins offer no special advantages. Disassembly of a connector housing, removal of the damaged pin, and replacement with a new crimp-on pin requires a good deal of dexterity. For this reason, newer connector designs tend to have larger-diameter pins. Another reason, larger pins have more contact surface area that lowers connection resistance improving conductivity through the connector.
Just as there are many circular connector designs, the same is true of rectangular connectors. Many, if not most, of these connectors are designed for a specific application, such as audio, video, data, power, etc. These can be further categorized by the environment in which they will be used, such as automotive, aircraft, entertainment settings, indoor, outdoor, etc. However, it’s possible for connectors to span applications. That is, connectors designed for one application can and have been used in unrelated areas. So a comprehensive review of rectangular connector styles and features is not practical. Nevertheless, comparing a few mechanical features of typical general-purpose, rectangular cable connectors to threaded cylindrical designs can help make product selections easier.
When a designer or user standardizes on a circular connector style for a set of applications, the idea of switching to a new design of any sort is not something to be taken lightly. This is particularly true in the entertainment industry where live events with unique setups can be stressful. Even with known connector problems, technicians have learned to deal with them to a certain extent. It’s a case of working with the devil they know.
However, adopting a rectangular connector design can eliminate several problems with few, if any, offsetting irritations. In fact, trunk-cable assemblies are a relatively easy way to start making the transition. Fundamental features of rectangular connectors are larger pin sizes and straight-line connection forces that eliminate the twisting problem associated with the threaded shells of cylindrical connectors.
Rectangular connectors have guide pins and connector keying that reduce the chance of misalignment and pin damage when hand mating trunk-line cable segments. Furthermore, these “push-to-mate” designs have no threads to get bent if the cable end is dropped. Many have locking levers that assure fast, positive mating of the two connector halves without a cross-threading problem. In addition to a more-reliable initial connection, the locking lever also provides higher vibration resistance than threaded-shell circular connectors. Damaged levers are easily replaced on the spot because the levers are external to the connector housing.
Locking-lever designs typically allow higher pin densities, and that conserves space. It also means only minimal hand space is needed to connect and disconnect. Installation and teardown times are reduced. Just plug and latch the connector to complete a connection. Some manufacturers offer an optional connector-coding feature that helps prevent mismatched connectors.
Many of these rectangular designs are suitable for outside use in wet and dusty conditions, meeting the requirements of a Type-4 environmental rating per UL50. For particularly demanding outdoor applications, look for rectangular connectors designed and tested according to IEC 60529, IP65 and IP67, and other pertinent standards. IP65 and 67 designate robust protection from dust and water.
Some connector manufacturers have standardized on modular designs to gain the benefits of common parts across a broad line of rectangular connectors. Standardized form factors, such as housing and hood sizes, are key elements in modular design. Various inserts and modular arrangements can reside within one connector form factor (size), thereby reducing inventory costs and simplifying bills of materials and assembly-handling costs. This is a great benefit for cable-assembly OEMs and users as well. They have familiar designs for a wide range of applications while gaining the benefits of interchangeable parts and reduced component inventory. These characteristics have important implications in assembly and field servicing.
Technicians and assemblers who put together multicore trunk cable assemblies find that circular threaded connectors can be relatively expensive compared to many rectangular connectors now available. Moreover, modular rectangular connectors are easier to assemble, saving time and labor cost. This becomes increasingly important as audio, video, power, and control cables are assembled into composite trunk-cable assemblies. Modularity also makes field servicing much easier, a strong motivator in trying out new designs.
Entertainment-industry connectors must accommodate a wide range of composite trunk-cable assemblies, with provisions for different types of conductors, insulation, electromagnetic-interference (EMI) protection, and grounding methods. Without standardized connector designs, cable assembly can be a hassle. Ideally, OEMs and users would like the same cable-assembly methods across a variety of conductor types and sizes without special tools, or with a common set of tools. Easy assembly is particularly important when terminating conductors in the connector contacts, which is problematic in some designs.
Several features found in rectangular connectors lend themselves to field assembly, repair, and troubleshooting. For example, many styles of field compatible terminations are available including screw terminals, cage clamp, axial screw, and Quick Lock terminations. All of these termination styles make it simple to connect wires to contacts without special or costly tooling. And they permit easy repair or replacement of individual modules or inserts, sometimes without stripping insulation from any wires.
Individual modules can be removed for repair or replacement, or others can be added to upgrade systems. Some manufacturers offer dummy modules for a housing. This permits the addition of a real module later to accommodate upgrades or optional accessories.
Hybrid rectangular connectors
Besides easy assembly, modular designs make a good choice for hybrid connector inserts — those that mix signal and power contacts in the same connector. Customized rectangular connectors can accommodate fiber-optic strands; Ethernet, coax, and audio lines; electric power; pneumatic lines and many other specialized connections. This flexibility makes it easier to create trunk cables that handle not only audio and video, but also power and control for rigging, lighting, and any other function.
Good shielding and grounding are a must where mixed signal and power leads coexist. Shielding is mainly a cable issue to prevent EMI from entering or radiating from the copper conductors. Typically signal lines in the cables are well shielded. For example, the twisted pairs for Ethernet would include a shield around the pairs, even though Ethernet twisted pair is usually operated without shielding. Shielding becomes a nonissue with fiber-optic cabling. However, if shielding is needed, keep in mind its effectiveness is only as good as the weakest link in the cable and connector assembly.
Good grounding may boil down to be a connector issue. Ease of assembly is a key factor in assuring good shield grounding at the connector hood and housing. The rectangular design automatically provides an electrical ground without loss of contact simply by installing the module or inserting into its housing and attaching a ground wire.
Individual electrical pin contacts are available in silver and gold plate for wire sizes from 26 to 14 awg with ratings up to 10 A and 250 V. Pins for fiber-optic strands are also available. The fiber-optic pins are as easy to insert and remove as the wire pins.
As true for any electrical connector, hybrid rectangular connectors must be designed with an application environment in mind as there are several factors to consider. In many cases, a cable designer or user can specify connector materials from a list of manufacturer options. The appropriate selection of connector housing material is critical to ensure long-term durability. Depending on the application, enclosures made of polyamide or polycarbonate plastics may be acceptable, while others may need a metal housing — typically a plated-zinc die casting.
For more-robust designs, look for housings that incorporate a metal frame instead of plastic. Metal frames protect against modules being pushed out the back end due to mishandling or mismating of the connector halves. Metal frames also automatically provide a grounding path from the housing to ground. No extra steps are needed to ground the outside housing. Even though a metal frame helps with grounding, it’s still advised to specify separate signal and ground contacts at each end of the modular frame. A hinged frame makes installation and removal of modules fast and easy, saving assembly and field-service costs.
Materials used for seals and cable clamps need special attention in outdoor applications. Ozone and UV radiation can seriously degrade the elasticity of seal materials. Many materials become brittle when exposed to sunlight or other weather conditions for prolonged periods. Therefore reliable sealing is no longer guaranteed.
A wide range of parts, inserts, pins, and so forth, lets cable designers take full advantage of the modular design. Check with each manufacturer on the availability of modules and other components needed for various applications, including different housing geometries. The greater the number of modules available from a manufacturer means the possible creation of a higher number of unique assemblies. A connector with two or three-dozen modules in its line theoretically can create millions, or even billions, of unique connector assemblies. So whether you need one or a thousand different connectors, the right connector is just a module away.
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