From screw clamps to spring clamps

Some people continue to do things the way they’ve always done them… just because that’s the way it has always been done. One example is continued use of terminal blocks with screw-clamp connections instead of spring-clamp termination.


Phoenix Contact calls its spring-clamp termination “spring cage,” and says such wire-clamping terminal blocks save 10-15% time compared to tightening screw connections manually. Its products include the Mini Spring Cage Terminal Block for mounting on a rail.

Some people continue to do things the way they’ve always done them… just because that’s the way it has always been done. One example is continued use of terminal blocks with screw-clamp connections instead of spring-clamp termination. Even spring clamps have been around more than 20 years. Multiple manufacturers offer them. I really think it’s now OKto switch from screw to clamp-style termination. Doing so saves time and money, and here’s another example of how.

Jacobs Sverdrup ’s Technology Group (with offices in Tullahoma, TN and Southfield, MI) is a system integrator providing design, design/build, operations, and maintenance services for aero-propulsion and space system facilities, automotive test facilities, and manufacturing sites. The integrator assembles and tests computer-based data acquisition and control systems in its Systems Development Laboratory in Tullahoma, TN, for installation in test facilities worldwide. A recent application involving a test facility for a “big three” automotive manufacturer caused the system integrator to re-evaluate the electronic connections it had been using in similar applications, specifically for an automotive wind-tunnel application. Historically, some wiring connections using screw-clamp terminal blocks tend to loosen during relocation from the development lab to the customer’s site. More connections loosen during the field connection process on location. Loose terminals extend on-site testing time required and degrade confidence about connection stability over time. By using Phoenix Contact spring-cage terminal blocks, Jacobs Sverdrup eliminated loose connections and realized other benefits.

For the project, Jacobs Sverdrup designed and built two environmental altitude wind tunnels and two temperature soak rooms. These facilities allow research scientists and engineers to test auto-mobiles under altitude simulation from -700 ft to +12,500 ft and under simulated temperature conditions of -40 °F to +130 °F. Wind speeds up to 100 mph are capable during the simulated environmental conditions. Full-sized vehicles can be operated at these speeds on the integral four-wheel drive dynamometer system. Validating vehicle performance and calibrating exhaust-emission controls is the main outcome of testing.

“We also wanted to reduce costs and assembly time as it took a lot of time to terminate the screw-clamp blocks,” states Tony Tenison, controls and instrumentation branch manager. “Ease of termination, a form factor for jumpering, and the breadth of the product line (knife disconnects, feed-throughs, fuses, and circuit breakers)” were among attributes Tenison saw in Phoenix Contact’s ST spring cage terminal blocks. Cost was approximately 10% less than the screw clamp. “Overall project savings for Jacobs Sverdrup, in terminations and jumpering, were approximately $4,500” in labor and trouble-shooting savings, Tenison says. “Lower-cost spring-cage blocks saved us about $500,” he adds. Internal cabinet wiring was also reduced as Jacobs Sverdrup implemented Phoenix Contact’s raised DIN-rail, eliminating the need to route cable around the components.

—Mark T. Hoske, editor-in-chief, Control Engineering,

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