How to Design for Rugged Environments Using Sealed Connectors

Designers are squeezing ever more electronics into increasingly awkward or tightly confined spaces, especially in transportation, industrial systems, and smart home appliances such as washing machines. In such applications, interconnect routing can result in many reliability and dependability challenges due to dust, moisture ingress, temperature extremes, and mechanical stresses.

Even within the same system, the requirements of individual connections can vary greatly. Cables carrying low-voltage digital signals have different interconnect issues compared to thicker wires carrying high voltages for motors and power distribution. The wrong choice of connector can result in full or intermittent signal failures, expensive downtime, and maintenance issues.

This article will discuss the challenges involved in selecting suitably rugged cable interconnect solutions that are robust enough for the application. It will explain how the appropriate use of an IP67-rated and USCAR-2 Sealing Class 2 cable connector system can ensure reliable interconnects that also lower the cost of maintenance and repair. It will then introduce a variety of IP67-rated and USCAR-2 Sealing Class 2 cable interconnect solutions from Molex and show how they can be used to address a range of application requirements.

Industrial interconnect design considerations

Designers of equipment for industrial environments must account for particulate contaminants, liquids, and extreme temperatures. In addition, industrial systems must be prepared to deal with unpredictable conditions due to changes in the environment or equipment.

Industrial facilities such as factories and warehouses use a variety of interconnect solutions, many of them heavy duty. Cars and trucks also qualify as moving industrial environments. There are general guidelines that must be considered for these interconnect situations. The most basic is resistance to any type of particulate matter, from iron filings and metal fragments to dust and fine powders. The finer the particulate matter, the higher the probability of it being airborne. For example, common dust, soot, and other fine particulates from heavy-duty equipment can be kept aloft by fans and ventilation systems and land many feet from their source. These particulates can enter any unsealed openings, including mated connectors, contaminating interior surfaces. This can cause mating issues ranging from intermittent malfunctions due to connection resistance to total loss of contact. Also, if the particulate matter is abrasive or corrosive, it can cause permanent connector failure requiring an expensive and time-consuming replacement.

Various fluids can also be found in industrial environments. Water, gasoline, oils, and various chemicals are common in heavy-duty industrial environments. Ingress of these liquids as fluid or vapor into a mated connector system can cause shorts and again result in equipment failures.

IP67-rated interconnect systems

Instead of making a variety of connectors for different industrial environmental conditions, the industry has standardized on using wires, cables, and connector systems that are IP67 rated. While the two letters IP officially stands for the three words “international protection rating”, it is most commonly known by its unofficial but more accurate “ingress protection”. IP67 defines the interconnect system’s resistance to particulate and foreign objects, as well as its resistance to water ingress.

The “6” in IP67 indicates that an interconnect is totally impervious to any particulate matter, including fine dust. This is accomplished primarily by a tight seal between the mating housings of the two mated connectors. The “7” indicates that an IP67 interconnect system can withstand immersion in water to a depth of one meter for up to 30 minutes. This is good enough for most industrial environments.

The tight seal between the mated housings of the two connectors helps, but water resistance is primarily accomplished by a connector gasket that is typically resistant not just to water but also resistant to many chemicals. Different gasket materials are resistant to different chemicals, so during the selection of an interconnect system the gasket material used is an important consideration.

Connecting low-power digital signals

Of course, not all cable interconnect systems have the same needs. Interconnect solutions for digital logic signals deep inside IP67-rated equipment typically need only handle 5 volts or less at currents around 500 milliamps (mA). These low-power signals use small lightweight cable connectors that typically don’t see much physical abuse. The connectors must be easy to mate for fast equipment assembly, and lightweight enough that they don’t place any stress on the low-current wires in the cable assembly. For these interconnect applications, Molex has the Mizu-P25 miniature wire-to-wire connector system. These waterproof IP67-certified connectors keep dust and water out of the mated assembly in a convenient compact housing.

An example of a mated pair of IP67-rated Mizu-P25 connectors is the Molex 0521160240 plug and the Molex 0521170240 receptacle two-position waterproof connector system (Figure 1). When fully mated the two connectors are only 25.5 millimeters (mm) long, appropriate for small, cramped enclosures.

Figure 1: The Molex Mizu-P25 0521160240 plug and 0521170240 receptacle two-position mated connector system provides solid protection against dust and water. The mated connectors are only 25.5 mm long and provide a solid, audible click when properly mated. (Image source: Molex)

The housing and cap for each connector are made of polyester, which has excellent resistance to water, is flame resistant, and does not fade or crack with prolonged exposure to sunlight. Polyester connectors are also resistant to breakage and will bend during normal use while resisting deforming. This makes the connector system robust enough for rough handling when mated during equipment assembly. Polyester connectors also have excellent shear resistance, ideal for the sliding abrasion that occurs when connectors are mated and unmated.

Both the connector ring seal and the wire end seal use silicone gaskets which provide an air-tight seal against water and dust. Silicone gaskets and seals maintain flexibility at low temperatures, making these connectors perfect for low temperature equipment such as refrigerators and outdoor cold weather equipment. These connectors have two positions with a 5 mm pitch, safely isolating the two signals. They are user assembled using crimped pins for ease of assembly.

The connector system is designed for easy mating, regardless of the crimp terminals selected by the system developers. When mated properly, the connectors provide a clearly audible click to indicate the connectors are solidly mated. This helps technicians during system assembly and ensures a tight mating seal.

This Molex Mizu-P25 connector system is rated at 250 volts and has an operating temperature range of -40°C to +105°C. This makes the Molex Mizu-P25 0521160240 plug and 0521170240 receptacle connector system appropriate for white goods and many cold weather industrial systems. The IP67 rating indicates to the equipment designers that the connector system is secure against water and dust and does not require extensive environmental testing of the connector system.

Rugged and sealed interconnect for ease of maintenance

Sometimes interconnect systems are required to handle higher currents and be maintenance-friendly in rugged environments. The interconnect system needs to not only provide a secure connection that won’t accidentally disconnect, but also be easy to disconnect during maintenance activities. For these situations designers can use Molex’s Squba sealed wire-to-wire interconnect system. The Squba connectors are also IP67 rated and can deliver more power in a smaller form factor. The Molex Squba 2042230004 plug and 2042200004 receptacle, for example, are four-position connectors with a pitch of 1.80 mm that provide reliable power and signal delivery (Figure 2).

Figure 2: The Molex Squba 2042230004 plug (left) and 2042200004 receptacle (right) are a four-position interconnect system designed to provide solid protection of high currents in wet environments. (Image source: Molex)

These Molex Squba connectors use crimped terminals and provide an audible click when properly connected. The connector latch on the receptacle is low profile, minimizing the chance to get caught on external equipment. The latch provides a firm, secure connection that can be easily disconnected during maintenance, either by applying a firm upward force using fingers or by using a standard delatching pry tool.

Both the Squba plug and receptacle housing are made of nylon, which is exceptionally strong and resistant to most industrial chemicals. This makes the Molex Squba interconnect system appropriate for any environment where the connectors may be moved, pushed, or impacted by equipment. The interconnect system is sealed against dust and moisture by silicone seals.

Each connector pin can supply 125 volts AC or DC. Recommended wire gauges are 22 to 24 AWG. Using pins crimped to stranded 22 AWG wire, each pin can handle a maximum of 5.25 amperes (A) at 30°C for a maximum current-carrying capacity of 21 A. Maximum current capacity varies with temperature, so designers need to pay close attention to the connector’s documentation to ensure the connector’s intended current throughput is appropriate for the conditions.

Operating temperature is rated at -40°C to +105°C, and together with an IP67 rating, the connectors are appropriate for environments such as HVAC systems, beverage dispensing equipment, and industrial equipment that must operate in cold or wet environments.

Multiple circuit submersible interconnect

Sometimes an interconnect system isn’t as simple as interconnecting the same signals on one cable. Occasionally, multiple circuit types must be transmitted along the same cabling including digital signals, high current control signals, and power supply connections. These situations require a hybrid interconnect system that can handle different sizes of contacts. For these applications, designers can use Molex’s MX150 Hybrid cable assembly interconnect system. The MX150 Hybrid system is validated to USCAR-2 Sealing Class 2 requirements, which is similar to the IP67 rating. USCAR-2 Class 2 requires passing a pressure vacuum test submerged in water.

When assembled, the Molex MX150 Hybrid is a fully sealed connector system, appropriate for situations where the mated connectors might become either submerged, or in a very wet environment where fluids and high-pressure water spray is common.

The Molex MX150 Hybrid 1601126001 12-position plug and 1601116006 12-position receptacle (Figure 3) can contain a mixture of up to ten 1.5 mm blade terminals and up to two 2.5 mm blade terminals. The 1.5 mm terminals can be used to carry low-level logic signals while the two 2.8 mm blade terminals can be used to carry up to 22 A. This makes this interconnect system appropriate for automotive and industrial applications where a single wiring harness needs to carry both power and data to a single machine.

Figure 3: The Molex MX150 Hybrid 1601126001 12-position plug (left) and its mate, the 1601116006 receptacle (right), can safely handle a mixture of 1.5 mm and 2.80 mm bladed terminals in a submersible interconnect system. (Image source: Molex)

When fully assembled and mated the MX150 IP67 Hybrid interconnect system is immune from contamination from dirt or dust. It can be submerged underwater and operate over -40°C to +125°C. The connector housing is a combination of nylon and glass, which is very durable and resistant to rough handling and mild impacts. This makes this interconnect system appropriate for harsh industrial environments and many consumer appliances, as well as automotive engine applications where the connector is subjected to extremes of temperature, high-pressure water spray, and hard impact from heavy objects.

The Molex MX150 Hybrid 1601126001 plug and 1601116006 receptacle need to be assembled as part of a cable or wiring harness. This assembly requires terminals to be inserted into the plug and receptacle. However, it’s possible for assembly technicians to sometimes not insert the terminals fully into the connector housing, leading to unreliable connections. For these situations, each of these connectors include a terminal position assurance (TPA) housing.

During a successful pin insertion into the TPA housing, the assembly technician will feel the pin firmly lock into position. If the terminal is not inserted correctly, upon mating the plug and receptacle will fail to latch. This guarantees that the pins are properly inserted, increasing system reliability.

Conclusion

Designers of systems for industrial, transportation, or home appliances need to ensure their connections can withstand the rigors of the application, including tight spaces, dust and dirt, temperature extremes, liquids and oils, and other penetrative matter. To help simplify the design process, designers can look for specially designed connectors rated to IP67 or to address both dust and dirt penetration, as well as moisture and liquid ingress.

As shown, there are a variety of IP67-rated connectors suited to a wide range of application requirements, from low-level digital signals to high-current power delivery. Selecting the correct IP67-rated connector assembly ensures system reliability and minimizes the risk of expensive downtime or repairs.