Selecting heavy duty connectors for industrial applications

March 08, 2016 // By Roberto Bonacina
The process for selecting industrial multipole connectors, wherever connections are required to power, control, data and signal circuits has to take into consideration a variety of aspects as well the physical and environmental conditions in which the connector must function.

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.