"Personally, I prefer push-in terminal blocks used with ferrules," says John Piller, founder of JPiller Design & Consulting, an industrial controls and automation integration and consulting company in Indiana (Figure 1). "They make assembly faster, provide a consistent connection and make field maintenance much easier. I also like double-level terminal blocks because they let me terminate and service a device from one location, which saves valuable panel space and simplifies troubleshooting."

For relays, Piller is a fan of the thin interface relays that use ribbon-style jumper bars. "They make it easy to distribute common signals or power across multiple relays, resulting in a cleaner panel, less wiring and easier future modifications," he notes.

Years ago, Patrick Bunn, owner of Bunn Automation Consulting in Alabama, did a factory acceptance test (FAT) for a project that included seven control panels and more than 1,000 points of I/O (Figure 2). "At the end of FAT, the client was looking at the panel wiring and said, 'This looks nice, but you are missing the heat shrink that goes over the wire labels that was explicitly called out in the wiring spec.' As a result, we had to de-terminate, add heat shrink, shrink it down and re-terminate every single wire,” says Bunn. “The final day of FAT was on a Thursday. The panels needed to be on site Sunday evening to be installed Monday. Unfortunately, I chose to make the co-ops and interns work the weekend to complete that task. The result was lots of wiring issues during field checkout."

Terminal blocks are very necessary in machine design, notes Larry Stepniak, electrical engineer at Flint Group in North Carolina (Figure 3). "When used inside a main control cabinet, they create a centralized distribution of incoming and outgoing wires," he explains. "This not only provides a convenient termination, but also adds a mid-wire test point for use with a multimeter or other measurement device. Terminal blocks can also incorporate a fuse with a blown fuse indicator, creating a quick method of visual troubleshooting."

In remote locations, terminal blocks provide a convenient termination point for sensors, valves or other devices, adds Stepniak. "This allows a sensor or valve replacement without the need to splice the wires or run wires all the way to the main cabinet," he says.

"There is debate about screw terminals versus push-in terminals," admits Stepniak. "In my experience, a screw terminal torqued to spec is more reliable than a spring-loaded push-in terminal. Preset or adjustable torque screwdrivers are available to ensure that the correct torque is applied."

Good-quality ferrules crimped with a high-quality crimping tool should always be used to ensure a proper grip in the terminal and to ensure that no stray strands of wire are exposed, Stepniak mentions. "These stray strands can be a potential source of a short circuit and, in some cases, a safety hazard," he cautions.

"From my perspective as a controls engineer and panel builder, the biggest advancement has been the evolution of cage clamp and push-in terminal blocks," says Bobby Cole, president and CEO of Think-PLC, a system integrator based in North Carolina (Figure 4). "The newer drop-in, pop-out designs from companies like Weidmüller eliminate the need for a screwdriver during insertion, reducing installation time while still providing a very secure connection. When you're wiring hundreds or even thousands of terminations, those saved seconds add up quickly."

Cole says he grew up in an era where the "old-timers" trusted nothing but screw terminals. "At the time, it made sense because that's what had proven itself," explains Cole. "But anyone who's spent hours wiring a control panel knows the frustration of tightening a screw only to realize the conductor was sitting on top of the clamp instead of under it. You'd think you were finished, give the wire a tug, and it'd pull right out."

Today's cage clamp technology is tried and true, Cole says. "It provides a consistent clamping force, performs well in high vibration environments, reduces installer variability and significantly speeds up assembly. For our shop, it's become the preferred termination method because it improves both productivity and long-term reliability," he notes.

World-record connections

Weidmüller Group used its own Snap In technology to achieve an official Guiness World Records listing and created a completely new record title that had not existed before: Fastest Time to Connect 500 Terminal Blocks into a Single Chain by a Team.

During a celebration marking Weidmüller Group’s 175th anniversary, a team at the global headquarters in Detmold, Germany, wired 500 terminal blocks with a total of 1,000 connection points in a verified time of 2 minutes, 55 seconds. The record was achieved by employees from development, product management and other specialist departments who were directly involved in developing Snap In technology.

The record attempt was monitored and certified by official Guiness World Records Adjudicator Lena Kuhlmann, who evaluates and certifies record attempts worldwide.

“This record category was defined for the first time for this attempt and was successfully completed,” Kuhlmann says. “The team fulfilled the requirements with precision and thereby set an officially recognized record. What is particularly remarkable is that the task was accomplished by the very people who developed and implemented this technology.”

For Weidmüller, the record is far more than a measured time. “It demonstrates what is possible when technological innovation, experience and teamwork come together. With Snap In, we have developed a technology that fundamentally simplifies industrial wiring,” says Frank Polley, vice president, business unit terminals at Weidmüller (Figure 5).

“This achievement sends a powerful message to the market: the future of industrial wiring is faster, simpler and more productive,” says Randy Sadler, president and CEO of Weidmüller USA (Figure 6). “Congratulations to our colleagues in Germany for turning breakthrough engineering into a Guinness World Records achievement.”

The Snap In connection technology enables the direct, tool-free connection of conductors without requiring any additional action from a clamping mechanism. The connection is confirmed visually by the green pusher popping out and audibly by a clear clicking sound.