Electronics Protection Online - A Complete Guide to Enclosures and Protection

Electronics Protection

Selecting Connectors for Harsh Environments
Leslie Alderman, Marketing Manager
Kari Nettleship, Marketing Specialist
LADD Industries

In a perfect electrical connector world, every heavy duty connector would be compact, hermetically sealed, resistant to temperature and vibration, easy to use and inexpensive. A design engineer would only need to know how many cavities, and what wire gauge is needed. Unfortunately, this is not the case and there is no universal connector that fits every application. It sometimes seems there are as many different connectors for harsh environments as there are harsh environments. Motion, temperature, chemicals and fluids all present the opportunity to impede the flow of data and electricity and are can create harsh environments. Electrical connectors need to protect vital data and power transmissions from all kinds of physical and environmental factors, and they need to do it without fail. One small leak or fault at any point in an electrical system can stop a production line, cripple a military vehicle or immobilize a fire truck.

The ultimate job of a sealed connector is to maintain electrical continuity and keep everything running smoothly. If the equipment is to perform well in harsh elements or environments the connector must be sealed. When the correct connectors are selected there are many added benefits for the manufacturer. These benefits include: simplified wiring, increased reliability, reduced warranty claims and minimized down time.

To select the proper connector many factors must be considered. Once the simple questions of wire gauge and pin count have been addressed, the environmental challenges specific to each application need to be identified:
• Will the connector be exposed to heat, impact or vibration?
• Will moisture and fluids be present?
• Will the connectors need to be field serviceable?

There are several connector features designed to combat environmental challenges; a few of the most important features include contacts, seals, connector styles and design aspects.

At the heart of any connector are the contacts. Since they carry the signal, the contacts are the vital part of an electrical connector. If the continuity of signal and power through the contacts is not maintained, systems and applications can fail. When selecting contacts, style, termination type and material all need to be considered. Contacts are available in solid, stamped and formed styles.

Solid contacts are loose piece individual contacts that are manufactured to be easy to use and field serviceable. Solid contacts are excellent for low volume applications or where high precision is required. Stamped and formed contacts are designed for high production volumes and are best when used with production tooling. When selecting the style of contact it is important to consider how often the connector will be mated and unmated and what type of field service will be required. For the termination type there are two categories, solder and crimp type. A solder style termination requires the addition of heat and solder to adhere the wire to the contact barrel. Solder terminations are less precise and have the potential to reduce the reliability of the tensile strength. When crimped properly, crimp style terminations offer an increased tensile strength and are highly resistant to increases in resistance as a result of temperature and oxidation.

Contacts are typically formed or tooled from two metals: a foundation metal forms the shape, and a plating metal provides the finish. Both metals need to be corrosion resistant and highly conductive to maximize signal and power transmission. The best combinations for harsh environments are nickel plating over a copper base for standard power applications, and gold plating over copper for low voltage and data transmission (typically under 5 volts). Both nickel and gold are stable in sealed environments and offer excellent conductivity. Gold plating, with its superior conductivity and durability, is the better choice in diagnostic applications where high mating cycles are a possibility. The contact selection will affect the time it takes to build the harness, the level of serviceability in the field and the conductivity of the signal.
Fluid resistant seals are crucial for connectors in harsh environments. High quality environmentally sealed electrical connectors should have several types of seals including wire, o-ring and interfacial seals. All the seals work together to form an airtight, watertight connector housing to prevent corrosion or contamination. Silicone seals are common and reliable in most applications where connectors will be exposed to water or other common engine fluids. High quality silicone retains its flexibility, insulation and sealing properties across a wide temperature spectrum and resists cracking when exposed to temperature changes.

Wire seals surround the wire insulation where it enters the back of the connector. This seal forms an airtight, watertight seal between the wire and the cavity. For the wire seal to be effective, it needs to fit snugly against the insulation without any distortion. Interfacial and internal o-ring seals are important for sealing the inside of the connector and assist with proper mating. The internal connector seals protect the mating faces and contacts from exposure to liquids and moisture, and because they are flexible and resilient they also absorb and dissipate shock and vibration.

Seal distortion can allow a path for contaminates to enter the connector. To prevent distortion attention must be given to wire diameter and wire strain. Distortion can occur when the wires are pulled sharply to one side from the rear of the connector, contorting the seal. Connectors may need several inches of straight, unstrained wire for the seal to function properly. A backshell that extends the length of the connector, or a strain relief that restricts wire movement, can assist in holding wires steady and creating proper seal performance. All seals require a snug fit between the seal and the wire. To ensure a snug fit it is important to use the correct wire insulation diameter.

Since wire insulation is available in many different outside diameters from extra thin to extra thick and everything in between, it is important to verify that the connector seal will accommodate the size wire being used. If the insulation is too small, fluid can leak in around the insulation; if the insulation is too large, it will distort the wire seal and compromise the environmental seal. Manufacturers often offer multiple size seal options for a single connector in order to accommodate different applications and wiring requirements.
Proper sealing protects the connector and contacts from contaminants and can reduce electrical failures therefore decreasing down time and repairs.

In the most basic sense, the connector body exists to protect the contacts from the environment and provide the support system for the pins to properly make and maintain contact. The connector body provides a solid housing that is shock and vibration resistant and able to withstand environmental chemicals and fluids. The connector body needs to be constructed of a material that, in concert with the seals, can absorb and disperse the force of impact or shock. Connectors are typically offered in two material types: metal and thermoplastic. Both materials offer excellent protection from heat and vibration, and are stable across a wide temperature range. Metal connectors are heavier and stand up well to impact, but are subject to corrosion. High-grade thermoplastics are lightweight and can be engineered to be flame resistant and extremely chemical resistant. The material selected for the connector body should be a direct response to the conditions and substances to which the connector will be exposed. The correct material will protect the wiring from temperature variations, shock, vibration, chemicals or submersion.

To ensure correct contact placement, many environmentally sealed connectors use secondary locks. Commonly referred to as a wedgelock or terminal position assurance, the secondary lock snaps into or onto the mating face of the connector to make sure the contacts slide together properly when the connectors are mated. A good secondary lock, properly inserted and locked into place, provides additional stability to both the contact barrel and the mated connectors.

The method by which two connectors mate and lock together is critical in harsh environments. Whether connectors are held together by a push-latch, a threaded coupling ring, or tightened and held together by a jackscrew, the lock must:
• Be secure, yet easy to engage and disengage
• Give an audible or tactile signal when it is securely fastened
• Hold the mated position securely without any play
• Prevent disengagement due to vibration or impact
• Be easy to service

A firm, secure locking mechanism will withstand vibration and shock and is critical to maintain a steadfast connector engagement in rugged applications.

In addition to the connector specifications and features there are additional items to consider when selecting connectors and designing harnesses. These include ratings, industry standards, and harness design.
The Ingress Protection (IP) system is a rating system that assigns a numeric value to electrical components and equipment based on the amount of protection provided against dust contamination and water penetration. The typical standard rating for an industrial connector for harsh environment use is IP67. For these applications IP67 or manufacturer’s equivalent testing is the appropriate level of protection.
Underwriters Laboratory (UL) is a third party verification company. UL offers several categories and product safety certifications. A UL certification listing can provide assurance of the proper connector selection.

If the products will be used in Europe then the components need to meet RoHS. This directive restricts the use of six hazardous materials in various types of electronic and electrical equipment. RoHS compliance will ensure the equipment is acceptable for use in EU countries.
Industry standards help to provide a pathway to streamline design requirements. Almost every industry will have its own set of standards designed specifically for common applications. One example is SAE J1939, which is an automotive electrical standard. While designing an electrical program it is important ensure compliance with applicable requirements.

After selecting the proper connector, there is one more thing to consider. One of the most frequently overlooked problems in harness design is wicking. Wicking can happen in both sealed and unsealed connectors and occurs when moisture is pulled into the wiring harness between the conductor and the insulation. Unsealed connectors can contaminate sealed connectors because they are frequently subjected to condensation, atmospheric moisture and temperature variations. Fluid enters the unsealed connector body and into the wire, through the harness to the sealed connectors. Since the unsealed connector is an easy entry point they can be the source of contamination and corrosion in an otherwise sealed harness. To prevent wicking, sealed connectors should be used wherever possible and vertical mounting should be avoided.

Harsh environments present a myriad of challenges when selecting electrical connectors. All aspects of the application can be affected by the environmental impacts in which it will be exposed. Connector selection can be simplified by focusing on the application needs, the design requirements and the connector features. When these items come together there is a connector to meet every application regardless of the conditions it will be exposed to. A few key features to remember when selecting the correct sealed connectors are:

• High quality contacts provide fast, low-resistance power and
data transmission
• Flexible waterproof seals block intrusion from contamination
• Solid connector bodies protect from vibration and shock
• Terminal positioning provides correct contact placement
• Reliable easy-to-use locking mechanisms permit easy servicing
• Proper ratings and standards ensure durability to the elements

By selecting a connector that meets all of the application requirements the following benefits will be realized: increased product confidence, reduced electrical failures, simplified assembly, minimized down time, fewer warranty claims and better field serviceability.

LADD Industries, Inc. specializes in environmentally sealed electrical connectors manufactured by the Deutsch Industrial Division, Hemet, Calif. Deutsch connectors are designed specifically for critical applications in harsh environments where dust, dirt, moisture, salt spray, and rough terrain can contaminate or damage electrical connections and systems. For more information please visit www.laddinc.com.