How Industrial Strength Cables Improve Efficiency, Reliability, and Overall Cost of Ownership

Industrial environments can be very unforgiving on components and equipment. Often, a lot of effort goes towards sourcing rugged components and electronic systems, with designers paying less attention to the selection of cabling and wiring. However, two cables that deceptively look the same may behave very differently in harsh industrial environments.

This article will briefly outline the impact of poor cable choice before describing what goes into the construction of a cable fit for industrial applications. It will then provide examples of innovative cable solutions that solve the problem of signal transmission in harsh environments, reliably and cost-effectively.

Why cable choice is so important

The wrong choice of cabling may appear to function fine at first, but from the very beginning may actually be causing signal degradation and power loss. Over time they can also introduce intermittent connection failures that are notoriously difficult to troubleshoot, causing expensive system downtime. This can be especially troublesome in high vibration environments. Also, if the cable does not have the appropriate outer jacket material, exposure to chemicals or extreme temperatures and physical abuse can expose the wiring and open the door to short circuits and sparking.

A better solution is to select an IP67 or IP68 rated industrial grade cable that is appropriate for the application. Industrial cables are high quality cables with a more robust construction and often use higher quality materials than their commercial counterparts commonly designed for home use. While both types of cables can on a quick glance appear similar, industrial quality cables are more heavy-duty, capable of withstanding heat, solvents, and liquids much better than similar looking commercial equivalents. They are also more tolerant of bending, twisting, and stretching forces that can damage less rugged cables.

From an electronic viewpoint, choosing the proper industrial cables also minimizes power and signal loss over any cable length. They are also much more resistant to electromagnetic interference (EMI).

When selecting a high quality industrial grade cable, it’s useful to understand what goes into making a cable.

Center conductor wires

Start with the material and diameter of the center conductor. The larger the diameter of the wires, the more current the cable can carry while minimizing signal loss over distance. Copper is the best conducting material for wires. Lesser quality cables may use aluminum, which is an inferior conductor compared to copper. Make sure to buy name-brand cables from an authorized distributer like DigiKey, as what looks similar to a name-brand cable could actually have aluminum conductors with a copper coating. While solid wires are better conductors than stranded wires, solid wires do not bend as easily, making them impractical for many situations. Stranded wires are easier to place and route because they are more flexible.

Exterior outer jacket

The outer jacket material and thickness are crucial for the long life of industrial cables. The thicker the outer jacket, the better protected the cable.

The cable’s outer jacket in industrial environments needs to handle many forms of harsh abuse that can quickly degrade the cable. Sunlight, particularly ultraviolet (UV) light, can cause outer jacket discoloration or cracks. Solvents including oil, gasoline, and cleaning chemicals can also dissolve the outer jacket leading to failures. High temperatures can lead to shortening of the cable, which becomes more of a liability over longer cable lengths. Extreme cold temperatures can cause the outer jacket to become brittle, leading to visible cracks that may result in the outer jacket shedding and breaking off.

The outer jacket must also be able to handle physical abuse such as the abrasive effect of pulling the cable around sharp corners. The wrong outer jacket can lead to openings in the cable revealing the shielding or conductor wires. Thick polyurethane is a reliable choice of outer jacket material for high quality cables because of its resistance to abrasion. Polyurethane is also resistant to solvents, temperature, light exposure, and abuse of all kinds.

Water resistance is often taken for granted. While almost every cable can appear water resistant, in reality extended exposure to moisture can also cause shortening of the cable. This can be difficult to diagnose, especially if technicians continue to replace the cable with the same commercial cable without realizing the error. To prevent this, IP67 industrial grade cables are recommended for most moist environments.

Even with the most robust industrial cables, cabling should be routed away from sharp edges. To avoid stretching the cable consider using more than enough cabling for the length routed. It’s not uncommon in factories and office buildings for requirements to change and re-routing of cabling becomes necessary.

For extreme environments where cables might be submerged, an IP68 rated cable should be selected, such as the CA0162C22315012 four conductor circular cables from Amphenol Sine Systems (Figure 1). This cable and connector system is able to withstand temperatures from -25 to +100°C, at the extreme end of the industrial temperature range. The cables use stranded 14 AWG wire for the four conductors.

Figure 1: The Amphenol Sine Systems CA0162C22315012 circular connector cables use thick 24 AWG wires for excellent conductivity. The connector strain reliefs are heat molded onto the cable outer jacket for maximum protection. (Image source: Amphenol Sine Systems)

Cable connectors and contacts

The cable’s connection to the connector can be the most abused part of the assembly. It is recommended to always remove a cable connector from a socket by pulling on the connector shell and not the strain relief. However, technicians in a hurry will sometimes pull on the strain relief instead. Sometimes the cable connector is placed in a tight space where removing the connector by pulling on the strain relief cannot be avoided. If this is repeated enough times on commercial cables, separation of the wire from the connector contacts is likely, leading to intermittent connections or total failure.

For these situations, strong cable to connector housings such as heat molded strain reliefs are recommended as they provide excellent strain protection when inserting and removing the cable connectors, and also seal out moisture under harsh conditions.

The number of connector mating cycles usually isn’t important for connectors fixed to the same receptacles for months or years at a time. But, at the other extreme are cables used with industrial test equipment that can see dozens of mating cycles in a single day. It’s important to obtain a cable with connectors that exceed the number of mating cycles by at least 50%.

Sometimes extreme conditions call for innovative products with unique solutions. Rosenberger manufactures a series of magnetic self-locating connectors that offer a virtually unlimited number of mating cycles (Figure 2). The self-locating magnetic connectors on the end of the Rosenberger cable assemblies can be easily placed into the sockets with zero insertion force. The magnetic connecter system self-guides the cable connector into the socket with an audible snap without any manual effort.

Figure 2: The self-locating magnetic connectors on the end of these Rosenberger cable assemblies can be easily placed into the sockets with zero insertion force. (Image source: Rosenberger)

Rosenberger’s L99-838-1500 industrial USB cable assembly is designed for on-the-go diagnostic equipment. Each end has a simple magnetic locking mechanism that allows for fast and easy mating and unmating to a compatible socket. This is especially useful for maintenance to diagnostic equipment used in office buildings, industrial control and automation systems, and other environments where mating cycles are unusually high.

Gold, nickel, and tin: Fret the contact details

The cable connector contacts are related to the current capacity and reliability of the cable. Tin-plated connectors are fairly common in commercial cables. For high reliability industrial cable connectors, gold is the best choice because it is an excellent conductor, and unlike silver or copper it does not oxidize or corrode. However, it’s no surprise that solid gold is unreasonably expensive. A better solution is to use gold-plated nickel contacts like those used in the 1203410303 M12 CAT6A industrial Ethernet cable from Molex (Figure 3).

The industry standard M12 connectors use nickel-plated gold contacts, which are superior to solid gold contacts with increased durability, improved metal stability, and high resistance to corrosion.

Figure 3: The gold-plated contacts on the 1203410303 Molex M12 CAT6A industrial Ethernet cable provide low resistance with high reliability in industrial environments. (Image source: Molex)

While copper and silver are marginally better conductors than gold, they are more likely to tarnish and corrode in harsh environments. Gold is an excellent conductor for industrial environments because it is resistant to many solvents and maintains its connectivity at high temperatures. For these and other reasons, gold is recommended for high reliability industrial applications.

In most cases, gold-to-gold contact connections provide high reliability, low resistance connections. Gold is not recommended for mating with softer contacts such as tin because a process called fretting can occur. Fretting is when two different metals come in contact and cause a chemical reaction, creating another material that increases the resistance of the connection.

Another form of fretting is when a very hard metal like gold rubs against a very soft metal like tin, causing some of the tin to scrape off and adhere to the gold, leading to the same chemical reaction.

Cable shielding

Noisy environments like factories and office buildings are filled with electrical noise. Electromagnetic interference (EMI) can severely affect the efficiency and operation of electronic equipment. Cabling can generate EMI or can be affected by it. The correct cable shielding can inhibit or eliminate most EMI. It’s important to select cables with proper shielding for the industrial environment, as equipment problems caused by EMI noise can be especially difficult to diagnose later.

There are two types of cable shielding. Aluminum foil shielding is common in both industrial and commercial cables and provides 100% coverage. For industrial applications, the side of the foil facing the wires is attached to a thin, non-conductive surface for better insulation from the conducting wires. To provide sufficient shielding, the thickness of the aluminum foil can make the cable stiff and difficult to handle. Some commercial cables use a thin layer of aluminum foil that is sufficient for household use, but will not provide enough EMI protection for a factory.

Braided copper wire mesh shielding is easier to work with and has more flexibility than foil shielding. However, braided shielding typically provides from only 70% to 95% coverage. For this reason, many high quality industrial cables use a combination of both thin aluminum foil shielding along with a copper braid, providing excellent EMI protection while maintaining flexibility.

Cable connectors have a shield ground at each connector. It’s important to utilize both shield grounds for maximum noise immunity.

Conclusion

The proper choice of cabling early in a project can prevent problems later. Industrial cables are superior in quality compared to commercial cables, with the advantages of higher signal quality and longer life. Engineers and technicians should carefully examine the specifications of the cables being considered for an industrial application to insure sourcing the right cables for reliability, long life, and lower overall cost of ownership.