by Tim Senkbeil, Product Line Manager, Lumberg Automation, a Belden company

A historical perspective on how M8 and M12 connectors became the backbone of today’s industrial automation systems and how they can improve your system design

The year 2015 marks the 30th anniversary of the M12 sealed interconnect system. Over those 30 years, the M12 system has established itself as the go-to option for harsh environments that need reliable, hardened solutions for connectivity. Let’s take a look back at how connectors were developed, how they evolved and how they came to be the preferred interconnect system in industrial automation today.

The M12 and its smaller cousin, the M8, trace their lineage back to 1982 when a German-based company introduced the RK30—a 7⁄8 in. circular, 3-pin, screw-type, “waterproof” connector. This pre-assembled, overmolded connector was rated to IP67, meaning it was dust tight and remained watertight even if temporarily submerged. Used to connect industrial sensors, this precursor to the M12 found its first industrial automation application at an automotive plant, a market that remains key for the M12 connector to this day. Prior to the M12, options were limited: engineers were forced to hard wire or constantly replace connectors that could not withstand harsh environments.

Three years later, the M12 connector was introduced and stole the spotlight at the Hanover Fair in 1985. The M12, released with 3- and 4-pin versions, used the smaller metric M12 thread and had a smaller current rating, but retained the IP67 rating. The 4-pin version allowed for more advanced sensors and actuators to be included in a single system. Little did we know that this product release would set the direction for industrial automation connectivity for the next three decades. The M8 would hit the market four years later in 1989.

Following the introduction of the M8, both it and the M12 became standardized under IEC 61076-2-101, which resulted in the two connectors being nearly universally adopted for industrial control systems.

Applications for M8 and M12 interconnect systems
M8 and M12 have become favorites for anyone in need of a rugged, sealed connector. In addition to automotive production, other industries that call for specific cables to best meet reliability demands include food and beverage processing environments, machine building, rubber and plastics, textile and printing presses. They’re also seen connected to spray valves on farm implements or coolant valves in HVAC systems. The wide variety of cable types, connector orientations and keying options allows M8 and M12 connectors to address a range of situations and applications.

Since the introduction of the 3- and 4-pin versions of the M12, many more variations and options have become available. The connectors are offered in both straight and right angle configurations and can now be found in 3-, 4-, 5-, 6-, 8- and 12-pin versions. In addition to IP67, M12 connectors are offered with IP65, IP68 and IP69K ratings. This allows the M12 to be used in the most demanding applications, even where high-pressure washdown processes are required. IP69K applications often require resistance to corrosion, which can be achieved by using stainless-steel coupling nuts. The M12 is also available in the following keying/coding options:

• A-code—primarily used with sensors and actuators
• B-code—PROFIBUS fieldbus connections
• C-code (dual keyway)—primarily used with ac sensors and actuators
• D-code—100 MB Ethernet/IP 4-pin
• X-code—Gigabit Ethernet 8-pin

This covers the options for the connector itself, but the number of options grows substantially when you consider all of the different cable types that are available.

A polyvinyl chloride (PVC) jacketed cable is the most popular cable used with M12 and M8 connectors. A variety of colors are available (for example, yellow, black, gray and orange) and PVC will stand up well in a typical industrial environment. A polyurethane (PUR) jacket is a good choice if constant flexing or abrasion are environmental concerns; PUR-jacketed cables can be found in a variety of colors and some versions are halogen-free. The automotive market in the U.S. has moved to cables that require either a power-limited tray cable (PLTC) or tray cable-exposed run (TC-ER) rating. Shielded cables are available and are frequently used for fieldbus cables (including Ethernet, PROFINET, PROFIBUS, and DeviceNet), but are also used for sensor and actuator cables in high-noise environments. Other cable options include high temperature, industry certifications and armoring. For the oil and gas industry, ensuring that cables can withstand high temperatures is critical, while the mining and shipping sectors are concerned with industry certifications.

Why use an M8 or M12 interconnect system?
The vast number of choices can make selecting a cord set a daunting task. But before selecting a cord set, it’s critical to evaluate the environment and understand why a cord set is required. Understanding the need will help to narrow down the selection significantly.

Thirty years ago, there wasn’t a choice. If you were involved in industrial automation, everything was hardwired. Most often, sensors and actuators came with long wires already attached or individual wires that weren’t even jacketed together. Those wires would be threaded through conduits and then wired into the system. This was a time-consuming process that required the services of an electrician, costing organizations significant time and money.

Building the system is one thing, but servicing it is another. If a sensor or actuator needed to be replaced in a hardwired system, the entire device would need to be disconnected, removed and replaced, and then rewired. Again, this required an electrician. In addition, any machine downtime causing repairs like this was very costly.

M8 and M12 to the rescue
A system that is connected with M12 and M8 connectors makes assembling, testing and servicing an industrial control system faster and less expensive. While the upfront investment of cord sets and connectors is greater than cables and wires, the cost savings comes from a reduction in labor and maintenance costs. A large system that might take a week to hardwire could be wired with connectors in as little as two days. The savings accrued by reducing the installation time is significant, but now, wiring a connected system does not need to be done by an electrician, which adds to the savings and further justifies the higher price point for M8 and M12 connectors.

Another advantage: Start-up and testing of a machine is faster. A lot of time spent during start-up is the result of miswired devices. Prewired and tested cord sets eliminate the majority of wiring errors. Additional cost reductions come from reduced downtime, as cord sets can easily be replaced without the help of an electrician. Connected sensors and actuators can also be replaced without rewiring the system.

Choosing the right cord set
Like most engineering decisions, there’s a balance between cost and performance. For instance, using an armored cable with stainless-steel coupling nuts for an application where cord sets are run in wire trays in a temperature- and humidity-controlled environment isn’t the most effective solution.

First, list out the environmental needs of your application, and start with the lowest cost solution for your application. An unshielded cord set with a PVC jacket is typically the lowest cost option. If your application requires cable flexing, moving to PUR-jacketed cable is a good choice with only a slight price premium.

For example, in a high electrical or electronic noise environment, a shielded cable may be required to ensure communication reliability with sensors or actuators. If the equipment will be exposed regularly to water or will reside in a high humidity or salt spray environment, consider stainless-steel coupling nuts for the cord sets.

Each of these additional features described will increase the cost of the cord set, but that slight increase in price will help you avoid replacing the cord sets due to product failure—or worse, intermittent failure.

Although 30 years is a long time for any product to exist in the market, the M12 and M8 product families continue to be used in new designs every day. With the continual addition of new product features, these connectors will be around for a long time to come.

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Lumberg Automation, a Belden company
www.belden.com