Selecting the most appropriate connector system depends on a number of key factors: the electrical requirements; shielding against electro-magnetic interference (EMI); and the physical characteristics such as the space, termination method, locking mechanism and protection against ingress of dust and water.
Back to basics
When it comes to electrical requirements, the required current influences the size of the contacts, the thermal properties determine the type of insulating material and the voltage dictates the contact spacing required to prevent creepage between contacts.
Copper-alloys plated with gold or silver are used for contacts to ensure high conductivity and corrosion resistance with over 500 mating cycles while inserts and contact carriers should ideally be made from polybutylene terephthalate (PBT) for its insulating properties, excellent chemical resistance and dimensional and temperature stability up to 85ºC.
Increasing demand from equipment manufacturers for shielding against EMI means more applications require shielded cable systems and connectors. For optimum results 360deg shielding is required, which is said to offer high attenuation over a wide frequency.
Good quality metal connectors are manufactured from brass for its strength and machining characteristics, while for reduced weight and cost, die-cast zinc or aluminium alloys are often used. For corrosion resistance and aesthetics, metal parts can be nickel or chromium plated or anodised and for more demanding applications, stainless steel should be considered.
Overall, the trend is towards low cost, light and robust all-plastic connectors, where polyamide is the preferred material, being tough, non-abrasive and resistant to solvents and temperatures up to 85°C.
IP facts and myths
Protection against ingress of dust and water is classified in IEC60529 with an IP rating. This is defined by two numbers, the first determining the protection against the ingress of foreign objects or ‘dust,’ rated between zero and six. The second number defines protection against water with zero offering no protection and the highest protection, IP69K, accrediting resistance to high-pressure water and steam cleaning.
A waterproof connector is commonly specified to IP67 or above, with IP67 defined as withstanding temporary immersion in water, typically, immersion to one metre for 30 minutes. For constant immersion in water, the norm is IP68 although, despite popular misconception, this is not a standard test that can be compared across applications. Instead, it requires agreement between manufacturer and user and can vary widely.
High IP ratings are usually only achieved when connectors are mated. A cap is required to provide protection while the connector is unmated, however, new systems like Binder’s 770 NCC series achieve IP67 when unmated. This is designed to negate the need for a protection cap and is achieved using a spring-mounted cover within the receptacle body.
The mating system has a significant influence on price. IP requirements greatly impact the type of mating system, as does the frequency of mating. High IP ratings are achieved with integral seals within the mating system for which Binder uses high performing elastomeric materials that also provide good chemical resistance.
Snap-in connectors provide quick and simple mating and are generally the lowest cost solution. Although bayonet connectors offer a more secure mating, the latest snap-in connectors can be rated IP67 and above, providing an economic solution with high performance.
Metal push-pull connectors can be expensive, while modern plastic versions provide a low-cost, quick mating IP67 connector. Screw connectors provide the ultimate protection against accidental un-mating and have excellent IP performance, but are generally more expensive.
Choosing a combination of materials, mating systems and connector design to provide optimum price versus performance can only be achieved with careful analysis of the specification, the task at hand and the operating environment. In terms of product functionality, performance and reliability, it will be time well spent.