Selecting heavy duty connectors for industrial applications
Potential fields of application for heavy duty connectors can stretch far and wide – such as general industrial automation, railway, automotive and commercial vehicle, marine and oil & gas sectors – generally whenever a strong connection is required. This makes heavy duty connectors a potential replacement to other kinds of connectors commonly used. Each operating environment requires the chosen connector to have resistance to varying levels of shock, vibration and temperature as well as the appropriate level of sealing protection from the ingress of dirt, dust, chemicals and other fluids.
A heavy duty connector comprises of four main parts: (1) the hood, which is the external plug cover of the connector, which includes specific metric, Pg or NPT thread(s) and cable gland(s); (2) the housing, which is the component installed on panels and equipment; and the two inserts, which are the parts to assemble the cable wires – the (3) male insert is usually assembled into the hood and (4) female insert into the housing. The thread on the hood should remain unpainted to guarantee a good ground connection when assembled with the cable gland.
At the core of any connector are the contacts within the inserts, as they carry power and signal. The choice of contact type, which is either silver, gold or tin plated copper alloy depends on what type of field service is required. Gold platings are used in signals with voltage and current lower than 5V and 5mA while for other applications the silver platings are commonly used.
Several types of inserts are available and one type can include screw and spring type contacts that are pre-installed into the inserts’ body. Crimp type inserts carry turned or stamped contacts. The latter being typically distributed into reels of hundreds or thousands of pieces. Molex offers special push-in inserts that do not require specialised tools – simply push the wire into the clamping point to connect the wire. Vibration and shock proof, this push-in system can reduce assembly time by as much as 80% over the standard screw types.
In addition to these inserts, Molex has developed a modular system. It is made of a support frame and a mobile element to block the modular inserts. Captive screws allow the modular connector to become a monoblock structure resistant to impact and vibration, as well as compression and traction when coupling male and female inserts. This modular interconnect system is also intermateable with the market leader.
At this point it is important to consider the end application holistically, in particular when a number of identical connectors are mounted closely together. If the coupling is not correct the consequence can be severe and may result in connector and application damage. Code pins, either single or double can be used instead of the normal insert fastening screws to ensure coupling of identical connectors.
Once the kind of insert has been determined to fit the specific need, male and female inserts are enclosed into a suitable hood and housing couple. A large variety of these enclosures are available with different combinations of components and materials. Each one is suitable to a specific industrial installation for normal environmental conditions as well as aggressive environments. The principle parts are made from die-cast aluminium alloy with a finishing of polyester powder (no finish for the EMC version) or in a self-extinguishing thermoplastic. They are resistant to impact and are mechanically strong from stress. Both the hoods and the housings are according to NEMA 250-1991, UL50, Type 4, 4x (for corrosion resistance) and 12.
Due to the large number of heavy duty connector sizes available, selecting the correct combination is important. Some connector manufacturers provide a size number (mostly with letters A and B), while others refer to the screw fixing centre distance.
One of the main criteria in selecting the proper heavy duty connector is the locking system. There are several locking mechanisms available, depending on requirements. The standard single locking system has a lever on the front or side of the housing. Rotation of the lever causes the housing and the hood to be locked together. Double locking systems have two levers that can be mounted either on the housing (standard locking system) or on the hood (reverse locking system) and provide additional security.
While many connector systems feature plastic levers or leverage with plastic parts, Molex provides the locking system with monoblock lever(s) made of galvanised or stainless steel: they are more robust and offer superior reliability. For high vibration environments, however, a screw or toggle locking system is typically used.
Die-cast pegs, which are integrated in the casting of the enclosure and are engaged by the lever to lock the connector, may become a source of weakness due to the material itself and to corrosion when locked by levers made of different materials. Moreover, after five hundreds locking cycles (i.e. minimum requirement as per European norm) these die cast pegs can wear down and decrease in diameter. The reduced diameter results in less compression of the sealing gasket and consequently affects the actual IP rating. If consistent sealing integrity and relatively high locking cycles are required in the application then the use of stainless steel pegs and levers can help overcome these issues. Molex heavy duty connectors are provided with stainless steel pegs.
For added security, automatic self-closing covers are available so that the IP66 protection is achieved should the operator forget to close the lever – IP69 protection is achieved once the lever is engaged.
Sealing is assured by special gaskets made of Nitrile Butadiene Rubber (NBR), which is designed to provide properties such as anti-ageing and resistant to chemical agents. The design of the gasket itself is a point often over-looked during the selection process. Gaskets can be easily assembled incorrectly thus compromising the IP rating. Simple positioning tabs on the edge of the seal can be used to help avoid incorrect assembly. It is logical for one to assume that a gasket with raised borders along its internal and external edges would provide better sealing integrity but this is not the case – the design of the gasket should allow water and dust to escape easily. The Molex gasket design provides both protection inside and proper pollution dissipation outside.
There are many connector features available on the market that are designed to combat the challenges mentioned above but few connector manufacturers that have the necessary credentials. Molex products are certified according to all the major certifications worldwide – coupled with depth of product offering and high component availability. Complementing the connector systems, Molex offers a wide range of standard and customisable aluminium enclosures with accessories.
About the author:
Roberto Bonacina is business development manager at Molex – www.molex.com
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