By Dan Hebert, PE, Senior Technical Editor
It's impossible to automate a machine without terminal blocks and connectors, so that makes them rather critical components. Although terminal blocks and connectors have been around for a long time, innovations do continue.
"Multi-level terminal blocks contain multiple levels of circuits within a single block and can reduce panel space by 50%," says Jessica Colón, product manager for terminal blocks and marking systems at Rockwell Automation (www.rockwellautomation.com).
In addition to simple control wiring, terminal blocks can ground, isolate and protect other components in the electrical circuit, Colón says. "To prevent electrical shock, terminal blocks are available with finger-safe connections," she explains. "They also can provide test points, adding additional safety to the circuit."
Other terminal block innovations speed installation. "Push-in terminal blocks with a leg-spring design reduce insertion forces by up to 50% compared with earlier push-in terminals, resulting in faster terminations and less operator strain," notes David Shoun, product marketing specialist for industrial connection technology at Phoenix Contact (www.phoenixcontact.com).
Push-in terminal blocks provide quick installation and direct termination of solid or ferruled wires, Shoun adds. "To terminate a stranded stripped wire, one can use a terminal block with an actuation button that opens the leg-spring connection," he says. "This can be especially valuable in installations with limited space or hard-to-access wiring areas. Push-in terminal blocks are available with up to 250 Newtons of pullout force, five times the IEC requirement."
Materials such as advanced engineered thermoplastics and design techniques produce smaller components with thinner cross-sections to maximize device current carrying, operating voltage and insulation voltage ratings, which allow for higher ratings in a compact package, thereby reducing control panel size and cost, says Sreeraj Panikkottil, design engineer at c3controls (www.c3controls.com).
"Material selection—for example, polyamide, zinc plating, stainless steel and electrolytic copper—along with the ability to reliably process those materials, ensures high component performance and durability to withstand the electrical, mechanical and environmental demands of the most severe industrial applications over years of continuous service," Panikkottil explains.
Modular and pluggable connectors and component plugs can be used with vertical and colored jumpers to cost-effectively customize machinery. "For example, modular connectors easily configure test harnesses and serve as permanent pluggable connectors," notes Michelle Goeman, product manager for terminal blocks and electronic interface at Wago (www.wago.us). "In addition, blocks with component plugs can be equipped with diodes for current protection, indicator LEDs, a resistor for signal conversion or leakage current, or a printed circuit board to create a custom circuit."
M8 and M12 type connection options come into play when using machine-mounted I/O blocks with IP67 protection, explains Kurt Wadowick, I/O systems product specialist at Beckhoff Automation (www.beckhoffautomation.com). "The durable I/O boxes and their dependable M8 or M12 connectors ensure a secure connection system in the most demanding environments," he says.
Specifying terminal blocks by function can simplify assembly, commissioning and troubleshooting. "Different types of terminal blocks can be assigned to varying types of input. So a sensor, programmable logic controller or voltage type can be color-coded," says Jacob Feutz, marketing specialist at Eaton (www.eaton.com). "A terminal block relay can be used to save space while still providing high-performance switching for a PLC output. A terminal block circuit breaker or fuse holder provides compact and modular protection."
Feutz says modern technologies including spring-cage and insulation displacement connections (IDC) provide a faster and more reliable connection. "Spring-cage connections keep constant pressure on the wire, even in high-vibration environments, while an IDC connection can dramatically reduce installation time," he adds.