Testing Terminal Blocks

By Paul Garcia

Deutsche Bahn AG (DB) knows about strength in numbers. DB is Europe’s largest transportation provider. With operations in 150 countries, it is one of the world’s most prominent mobility, networking and logistics organizations. In Germany alone, DB moves approximately 5 million passengers and 857,000 tons of freight daily. Globally, DB transports 1.835 billion passengers — approximately 28 percent of the world’s population — each year.

“Back in 1979, DB was one of the first to validate Cage Clamp performance in a large-scale application,” explains Michelle Goeman, Wago product manager – Terminal Blocks and Electronic Interface. “Those same terminal blocks have reliably served DB’s coach passenger cars for low-voltage installations, power supplies and lighting systems.”

After nearly three decades of continuous service in a harsh environment, Wago sought to examine the integrity of the 280 Series terminal blocks. Officials pulled the terminal blocks and subjected them to tests adhering to IEC 60947-7-1:2002 standards.

“Wago wanted to show DB how well the blocks held up after nearly 30 years of performing precisely as intended,” she says. “We pulled and examined them closely to show that despite millions of miles of service, they were still within original specs.”

Acceptance Criterion Fulfilled
In order to confirm overall product integrity, lab technicians took the 280-102 test specimens to Wago’s Electrotechnical Laboratory in Minden, Germany. The specimens were subjected to: a voltage drop, Dielectric (with ac voltage), rated impulse withstand voltage and pull-out tests.

All tests conformed to IEC’s exacting standards and all were passed with the terminal blocks fulfilling IEC’s acceptance criteria.

The 280-102 blocks were mounted to DIN-rail, fitted with solid and stranded conductors and subjected to voltage drops — 28 AWG at test current 6A and 12 AWG at 24A. The voltage drop test followed IEC 60947-7-1:2002, clause 8.4.4 stating, “Voltage drop shall not exceed the value of 3.2 mV per through connection at 1/10 rated current of the conductor.”

“This test helps determine connection integrity by simulating the extreme vibrations and temperature cycling these products are subjected to while maintaining a gas-tight connection,” Goeman says.

The 280-102 terminal blocks were also subjected to a “Rated Impulse Withstand Test” (IEC 60947-7-1:2002, clause 8.4.3 a). The 50-microsecond, high-voltage test verifies the distance between two poles within a terminal block. Five test specimens were installed on DIN-rail and subjected to 9.8 kV of applied test voltage. No flashover or breakdown occurred; therefore, the test was passed.

Next, the 280-102 blocks underwent a “Dielectric test with AC voltage” (IEC 60947-7-1:2002, clause 8.4.3 b). During the dielectric test, the specimens are subjected to a lower voltage over a longer duration in order to gauge the strength of the insulating materials. Again, the test was passed with no flashover or breakdown while the test voltage was applied.

“While these tests are excellent indicators of the 280 Series’ electrical properties, Wago also sought to test the 280-102’s strength through the pull-out test,” Goeman said. “This test simulates aggressive real-world operating conditions that can cause disconnections.

The pull-out test (IEC 60947-7-1:2002, clause specifies that one minute of pull force (without “jerks”) must be applied to a connected conductor. Performance is defined by the conductor not slipping out of the terminal unit, or the clamping unit breaking while undergoing pull forces up to 11.5 ft.-lbs. of force. As with the other IEC-style tests, Wago test specimens passed the pull-out test.

Extensive Engineering Yields a High-Performance Clamp
Goeman attributes the Cage Clamp’s dynamic contact and proportional clamping characteristics as two features that enabled the nearly 30-year-old terminal blocks to reliably serve DB and pass IEC-designed tests. The terminal blocks do not have screws to consistently monitor and tighten, providing DB with maintenance-free connections.

Dynamic contact allows Cage Clamp to automatically compensate for metal’s inherent properties to expand/contract with ambient and current-induced temperature changes by adjusting for settling strands and changes in wire size. This ensures consistent connection forces, despite temperature cycling. Proportional clamping supplies larger wires with the greater clamping pressure needed to transmit high currents while protecting small, finely stranded conductors. The pressure embeds wires in the current bar’s tin-plating for gas-tight seating of the conductor.

Extensive engineering in the cage clamp allows the unit to withstand vibrations of up to 2000 Hz and accelerations of up to 109 Gs in each axis without wire damage or contact failure.

Paul Garcia is a technical writer with Wago Corp.