“Today, a variety of different connectors are used to connect cables and components used in industrial automation. These connectors must be able to transmit all electrical power and data signal flows carried on the cable while terminating the lines in a manner that ensures tight and protected conductor connections. The challenge is that industrial automation-related equipment is often located in dirty, hot, moving, and electrically noisy environments… Therefore, industrial cable connectors require durability and reliability that other applications don’t.
Author: Lisa Eitel
Today, a variety of different connectors are used to connect cables and components used in industrial automation. These connectors must be able to transmit all electrical power and data signal flows carried on the cable while terminating the lines in a manner that ensures tight and protected conductor connections. The challenge is that industrial automation-related equipment is often located in dirty, hot, moving, and electrically noisy environments… Therefore, industrial cable connectors require durability and reliability that other applications don’t.
First, let’s understand some of the basics of industrial connectors: connectors include components classified as couplers (connecting two cables), and the kind of system that includes a plug and socket (or receptacle) for the connector components. In some cases, a connector can also be referred to as a cable gland – the terminating portion that goes through the housing… usually with a freely rotatable sub-assembly that compresses the O-ring at the end of the cable, allowing the cable to Isolated from chemicals, flames, dirt and external electrical currents.
Industrial cable connectors connect together (more commonly) cables located on front and rear mounted equipment receptacles. All connectors and cable glands have an intrusion protection (IP) rating as specified by IEC 60529 to quantify dust and moisture resistance. These ratings are the same as those used to describe the ruggedness of component enclosures as well as industrial equipment enclosures. An IP code has two numbers, and the larger the number, the higher the level of dust and moisture resistance.
The first digit of the IP rating specifies the level of protection against solids such as dust – from 0 for no protection to 6 for dust tight.
The second digit of the IP rating specifies the level of protection against liquids – from the number 0 for no protection to the number 8 for continuous protection against water to a depth of 1 m.
Figure 1: This figure illustrates what the various IP classes of IEC 60529 mean. The IP rating of the cable connector is critical. (Image source: connectortips.com)
Comparison of RJ and M12 Ethernet Connectors for Automation
Today, Ethernet, as defined by IEEE 802.3, remains the most widely used local area network (LAN) technology in the world. Ethernet-based industrial automation communication standards include ModbusTCP/IP, EtherCAT, Ethernet/IP, and Profinet. The connector commonly associated with Ethernet cables is the ubiquitous registered jack (RJ) connector. Most RJ connectors include a plug. The plug has a simple plastic tab that snaps into a mating port with a special geometry on the RJ jack to securely hold the two together. Plugs and receptacles are easy to mate with cables – installers can clamp them at the same time and use a special crimp tool to make electrical contacts. With crimp terminators, the cable can be cut in the field, and the resulting cable is extremely reliable. Plug subassemblies designed for this field installation are usually inherently transparent, so installers can inspect all internal contacts before the cable is used. That said, the reliability of factory-assembled cables is unmatched.
Figure 2: The TL2253-ND hand crimp tool can cut to length in the field RJ plug terminations of four-, six-, and eight-wire Ethernet cables. With a single squeeze, the blade of the crimping tool strips flat or round Cat5e and Cat6 cables and secures the connector securely. (Image credit: Tripp Lite)
If RJ connectors are not durable enough for a particular industrial environment, M12 connectors may be a better choice. That’s because M12 connectors enable a more reliable, robust connection — plus the advantage of being dust- and water-resistant.
Figure 3: The most common RJ connectors on Ethernet cables. That said, other types of connectors are also available for Ethernet cables. (Image credit: Getty Images)
Power over Ethernet (PoE), as defined by IEEE 802.3, is a convenient way to get data and power over a single cable. PoE Alternative A (often referred to as Mode A) uses the same two twisted pairs for data and power, so a lower core count cable can be used – bandwidth is limited to 100 Mbps (100BASE-TX). PoE Alternative B (often referred to as Mode B) uses a Cat 5 Ethernet cable with four twisted pairs – two for data transmission and two for power. This reduces the bandwidth used for data — even gigabit Ethernet-class cables limit data rates to 100 Mbps.
4PPoE or four-pair cable requires four twisted-pair cables, and both transmit power and data at the same time. This means higher data rates (Gigabit Ethernet and above) and higher currents can be supported. Devices receiving PoE power must be configured to accept either Mode A or Mode B as they were originally. That is, such cables may have fixed or alternating cross-pair resistances to indicate compatibility and require specific power configurations. Of course, what really determines the PoE mode of the system is the PoE power source (source equipment or PSE).
Figure 4: The design of a connector is largely determined by the cable it terminates. M12 Ethernet cable connectors, like the ones shown in this article, are generally stronger than RJ connectors; some manufacturers color-code them to indicate compatibility with PoE modes and conductor arrangements. (Image source: Lumberg Automation)
A connector that terminates both data and power cables (as well as network wiring such as Industrial Ethernet, PROFINET, and Fieldbus) is the M-series connector—a circular mating connector with a threaded female ferrule (for mounting on a male socket) and contains a set of conductive pins. M8 (8 mm) and M12 (12 mm) threads are the most common, but M5, M16 and M23 are also more familiar standards. The rigid (screw-on) housings of the M-Series connectors ensure a highly reliable connection, providing excellent protection and minimizing discontinuous signals even against environmental debris so common in corrosive and scour environments. So it’s no surprise that M-Series connectors are the highest standard for actuator, PLC, sensor, switch and controller cables in industrial automation.
M8 and M12 connectors offer a choice of 2, 3, 4, 5, 8 or 12 pins (pin positions). Sensors and power supplies typically require 3 or 4 pins. For M-series connectors on the Ethernet and PROFINET cable ends, four or eight pins are required. In contrast, those used to transmit fieldbus, CANbus and DeviceNet data typically have 4 or 5 pins at the end of the cable. Of course, cables carrying multiple streams of data and power may need to be terminated with an M-series connector with all 12 pins.
Figure 5: The Brad Ultra-Lock 120108 Right Angle Connector is a proprietary modification of the M12 connector design for improved reliability. (Image credit: Molex)
In fact, a related connector socket design that is fairly common in the industry is the pin array and socket pair – originally introduced by Molex, so this type of connector is sometimes colloquially referred to as the Molex interconnect. The Molex Brad range of proprietary connectors is based on the M12 connector, but replaces the threaded sleeve with a more convenient and reliable press-to-lock system. Reliability is ensured and the risk of signal interruptions is minimised as the locking effect is independent of the operator’s tightening thread action. Brad connector variants include:
・ Brad Micro-Push M12 Connector – A push-pull connector with IP65 protection
・ Brad MX-PTL M12 push-to-lock connectors with IP65 protection
・Brad Micro-Change M12 threaded connectors provide IP67 protection
• Brad Ultra-Lock and Ultra-Lock EX M12 connectors feature push-to-lock fittings and O-rings with full IP69K rated intrusion protection.
High frequency signal coaxial connector
Coaxial cables (with coaxial connectors) are also used in industrial automation to transmit high frequency signals – especially coaxial cables that support vibration monitoring and analog signal transmission. Standards abound.
BNC connectors have a bayonet fastening structure that requires a quarter turn to connect or disconnect. This connector can be used for frequencies above 12GHz, and in some cases up to 18GHz. DIN 0.4 – DIN 2.5 connectors are very small press-fit connectors suitable for frequencies below 3GHz. In contrast, DIN 1.0/2.3 connectors are small press-fit RF connectors widely used in digital telecommunications.
Proliferation of Modular and Custom Cables for Automated Machinery
In the traditional system integration approach, cables are “prepared” in the field – measured, cut and terminated during the installation of automation equipment. This usually means that the field electrician cuts the required cable to a specific length, strips all conductor jackets, and joins the cable with the connectors needed to connect the components at hand. This field cable preparation is time-consuming and leads to inconsistent connection quality. That’s why sourcing modular cable and connector systems consisting of standard cables and factory-installed connectors is a trend today. The required cable length has been determined during the design process and can be installed directly upon arrival.
It is estimated that modular cables can reduce field installation time by 60% to 70%, while increasing the reliability of electrical connections.
Special cases for cable glands
A cable connector called a gland is used where the cable needs to pass through the housing. The gland does three things: secures the cable, protects the cable from fraying, and creates a seal around the cable to protect the components inside the enclosure from environmental debris. The cable gland’s way of securing the cable essentially prevents damage to the electrical contacts from pulling or other disturbances. The cable gland also prevents the cable from scratching or rubbing against the sharp metal plate edge of the hole in the housing. This is important because the metal plate can easily scratch the cable jacket and eventually short out the cable cores.
Less demanding applications often use sheet glands with multiple fingers to secure cables. This type of gland is less expensive but requires periodic retightening to maintain the intrusion protection rating. Higher quality glands use continuous seals to secure the cable. This type of gland is also almost impossible to loosen after long-term operation.
The Structure of Today’s Industrial Power Connectors
In addition to data connections, equipment used in industrial automation often needs to be connected to power through wires. The relatively new PoE technology described above is probably a better choice because it makes wiring very simple. However, the vast majority of automation components and systems require traditional power cords.
Standardized connectors specified by the International Electrotechnical Commission (IEC) are common on power cables for consumer, office, and industrial applications. IEC defines a series of non-locking connectors in the IEC60320 standard with a voltage of 250V and a current not exceeding 16A. Here, C13/C14 connectors are typically used for Electronic equipment – including computer power supplies. Larger C19/C20 couplers are used for cable ends that carry higher currents — including server enclosures, for example.
Figure 6: Universal power cords include a variety of IEC and other standard connectors. (Image credit: Getty Images)
For more critical or demanding applications, IEC 60309 connectors are often preferred. These plugs, sockets and couplers are designed for industrial use and can carry 1000V, 800A and 500Hz. All of these connectors are somewhat waterproof. IP44 connectors are splash-proof, IP67 connectors are waterproof, and IP66/67 connectors are reliably protected against water ingress even when struck by a pressurized water stream. The receptacle can also be interlocked so that the receptacle cannot receive power unless it is mated with the plug — and the plug cannot be pulled out until the power is cut off.
Figure 7: Note the color coding of this high power cable connector (according to IEC 60309). (Image credit: Railway Tech)
Different sizes of IEC 60309 connectors are suitable for different current ratings. Connectors are also keyed and color-coded to indicate their voltage and frequency ranges:
・Yellow indicates 100 – 130 V at 50 – 60 Hz
・ Blue indicates 200 – 250 V at 50 – 60 Hz
・ Red indicates 380 – 480 V at 50 – 60 Hz – usually a three-phase configuration
When selecting connectors and sealing heads for industrial automation, there are many geometries and integrations to choose from. In specifying the cable size for a given automation machine, the first consideration for the design engineer must be the number of cable cores and the size of the cores. Second, the intrusion protection performance and reliability of the locking mechanism to prevent intermittent signal must also be considered.