Feature: Connectors, cables and enclosures


the set nominal value, a microprocessor calculates a trip time based on the magnitude of the overcurrent and switches the output off through a semiconductor switch. Because the trip decision is based on measured current, the device responds precisely and repeatedly to modest overcurrents on long runs and small cross-sections. Space matters, too. WAGO’s multi-


channel ECBs place eight channels in 32mm, using around 80% less DIN rail than equivalent miniature circuit breakers, with each channel adjustable between 1A and 10A. Two channels can be paralleled for 16A loads. Multicolour LEDs show the state of each channel, an overload warning threshold flags circuits approaching their limit, and a digital input and output allow remote reset and fault signalling to the controller. The practical guidance for designers is to size each channel to the cable as well as the load, and to wire the signal output back to the PLC so that a tripped channel is visible without anyone opening the cabinet.


Break out data cables with system wiring Data connections present a different challenge. A 32-channel digital I/O card wired point to point involves at least 64 individual terminations before shields and commons are counted. Each one is an opportunity for a transposed conductor, a poorly dressed strand or a loose screw. System wiring replaces much of that


effort with pre-assembled cables and interface modules. WAGO’s universal interface modules accept standard plug- in connections such as RJ-45, RS-232 and ribbon cable connectors, and transfer the signals onto terminal block connections using WAGO’s Cage Clamp spring pressure technology. Controller-specific system cables, available for all major automation platforms, plug directly into the I/O card at one end and the interface module at the other. The connection is made and tested once in the factory, then simply plugged in on site. Three decisions shape a good system


wiring design. The first is whether to use controller-specific cables or universal cables with open ends. Controller-specific cables minimise site labour, while open-ended versions give flexibility where the controller has not been finalised or where the cable must pass through a gland. The second is density, since interface modules concentrate many signals into a narrow footprint and can free substantial panel space. The third is identification. Clear pole marking on both the module and the cable shortens fault finding considerably, particularly for maintenance teams who did not build the panel.


Protect analogue signal integrity Analogue measurements are the most vulnerable signals in any installation. A 4-20mA loop crossing a cabinet shared with variable speed drives can pick up interference, and any difference in ground potential between sensor and controller creates a ground loop that shifts the reading. Galvanic isolation is the most effective remedy. An isolation amplifier electrically separates input, output and power supply so that no circulating current can flow between them. Zero and span adjustment then compensates for signal offsets, and switchable filtering suppresses residual interference. Temperature measurement deserves


particular care, because the connection method directly affects accuracy. A Pt100 sensor changes resistance by approximately 0.385Ω per degree Celsius, so just 1Ω of lead resistance in a two-wire circuit introduces an error of around 2.6°C. Three-wire connection compensates


for lead resistance when the conductors are matched, and four-wire connection removes it entirely by measuring voltage separately from the excitation current. WAGO’s temperature signal conditioners support two, three and four-wire connection for platinum and nickel RTDs, KTY sensors and resistors, as well as thermocouples. Wire break and short circuit detection alerts the


controller if the sensor circuit itself fails, which prevents a broken probe being mistaken for a genuine process reading. For pulse and speed measurement,


frequency signal conditioners accept signals between 0.1 and 120kHz from NAMUR, NPN or PNP sensors and convert them into a standard analogue output. Voltage conditioners measure AC or DC voltages up to 300V in a module just 6mm wide, and the range operates between -40°C and +70°C for harsh environments. One detail that is easy to overlook is supply distribution. Because the modules share a common profile, their supply voltage can be commoned with jumpers across the whole range, removing dozens of individual power terminations in a large panel. Configuration can be carried out through software, DIP switches or push switches, with WAGO’s Interface Configuration Software connecting via a USB service cable.


Choosing the right switching element Between controller and load, relays and optocouplers provide both isolation and switching capacity. The right choice depends on the load and the switching frequency. Electromechanical relays offer full galvanic separation and handle a wide spread of loads, with WAGO’s portfolio covering switching currents between 1mA and 16A, including lamp loads and their high inrush currents. For dry circuits carrying very small signal currents, contact material matters, since standard power contacts may not self-clean at low currents and gold-plated contacts are the usual choice. Solid-state relays suit DC loads and


applications that switch frequently, operating into the kilohertz range with no contact wear and silent operation. They are a good fit for rapid decoupling of encoders and sensors. Optocouplers in 6mm housings offer fast signal-level isolation and are well established in railway and shipbuilding applications, where space might be tight and where vibration can occur. Maintainability should be designed


www.electronicsworld.co.uk November 2026 37


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