The plugs and sockets easily fit to cables — and installation personnel can simultaneously clamp them and make the electrical contacts using a special-purpose crimping tool. Crimping terminators allow for the construction of custom- cut cables (fitted onsite) that are reasonably reliable. Plug subcomponents designed for such onsite installation often have clear bodies to let installation personnel inspect all internal contacts before putting them into service. That said, the reliability of factory- assembled cables is unbeatable. Where RJ connectors aren’t rugged enough for a particular industrial environment, M12 connectors may be better. That’s because M12 connectors provide a more reliable and physically robust connection — with the added advantage of protection against the ingress of dust and fluids. Power over Ethernet (PoE) defined by IEEE 802.3 is a convenient way to obtain both data and electrical power through a single cable. PoE Alternative A (often called mode A) uses the same two twisted pairs to carry both data and power, so cables with fewer cores can be used — and bandwidth is limited to 100 Mbps (100BASE-TX). PoE Alternative B (often called mode B) uses a Cat 5 Ethernet cable
with four twisted pairs — two pairs carrying data and two pairs carrying power. This reduces the bandwidth available for data — limiting the data rate to 100 Mbps even when the cables are rated for Gigabit Ethernet. 4PPoE or four-pair cable requires a cable with four twisted pairs of conductor strands and all transmitting both power and data. This means that higher data rates (Gigabit Ethernet and beyond) and currents are supported. Devices accepting power over PoE must be configured to accept mode A or mode B as it’s supplied. That said, they may use fixed or alternating resistance across wire pairs to indicate compatibility and request a specific power configuration. Of course, it’s PoE power supplies (the sourcing equipment or PSE) that actually determine the system’s PoE mode.
Terminating both data and power cables (as well as network cabling such as industrial Ethernet, PROFINET, and Fieldbus) are M-series connectors — round mating connectors with a threaded female sleeve (to mount on a male receptacle) wrapped around an array of conducting pins. M8 (8 mm) and M12 (12 mm) threads are most common but M5, M16, and M23 are also familiar standards. The positive (screw-on) closure of M-series connectors ensures a highly reliable connection that minimizes intermittent signals even while protecting against the environmental debris so common to washdown and corrosive environments. No wonder M-series connectors are a top standard on the cables for actuators, PLCs, sensors, switches, and controls of industrial automation.
Figure 4: The connector design is largely dictated by the cable it terminates. M12 Ethernet-cable connectors such as the ones shown here are generally more robust than RJ connectors; some manufacturers color-code them to indicate compatibility with PoE modes and conductor arrangements. (Image source: Lumberg Automation)
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