Fast, flexible terminal blocks
Avoiding the need for hard wiring, the latest terminal blocks provide safe, secure connections with greater ease. Terminal block designs also offer more flexibility, space savings, accessory options, and integrated intelligence compared to prior designs.
Although they are often overlooked, terminal blocks are a critical part of the electrical control system, says TJ Landrum, product manager for DIN logic products, Eaton Corp . Important time and space-saving technologies are in wider use, Landrum says, including insulation displacement connections (IDC), push-in jumpers, and a vast array of integrated functions. “IDC allows for a secure connection with the flip of a screwdriver; the wires do not need to be stripped, and the risk of screws backing out is eliminated,” he says. This reduces installation time about 60%.
Other available control and protection features include fuse terminal blocks, circuit breaker modules, diode terminal blocks, and disconnect blocks. These “help integrate more functionality into a compact DIN rail assembly,” Landrum says.
In the last five years, Phoenix Contact also has observed greater IDC acceptance, and growth in what it calls hybrid terminal blocks. Larry Freeland, Phoenix Contact Clipline product marketing manager, says, “In our testing we’ve found IDC can be up to 80% faster than using a screw clamp connection with a manual screwdriver and ferrules. It is also up to 70% faster than spring-cage with ferrules and 50% faster than spring-cage without ferrules.”
Hybrid designs feature different connection technologies (such as IDC-to-screw, IDC-to-spring, and screw-to-spring connections) on each side of the terminal block. These are typically used when the machine builder or panel builder is not installing field wiring. The panel builder may use IDC inside the panel while building it and use screw connection for the conductors that come from the outside, which may be favored by the field installer, Freeland says. Other flexible, hybrid systems include interchangeable bridging system connections and an easier plug connection.
Plug and play designs are useful when large machines are broken down before shipping. “Pluggable connections simplify the process so the entire machine doesn’t need to be rewired on site,” says Freeland.
Smaller blocks, more choices
|Opto 22 Snap Terminal Extenders provide bundled connections from I/O module terminals to custom break-out boards.|
Over the past five years or more, terminal blocks have gotten thinner, narrower, and gained increased functionality such as added fusing, which eliminates the need for external fusing, according to Opto 22 ’s Arun Sinha, sales engineer, and James Davis, application engineer.
Terminal block makers have expanded portfolios by offering wiring harnesses, terminal extenders, other accessories, and, most significantly, control capabilities, they say.
“Controllers are now to the point where they are small enough to add to the DIN rail right there with the terminal blocks—as opposed to 5-10 years ago when terminal blocks served mostly as a termination point for field and control wiring,” they say.
|Rockwell Automation has a long line of terminal blocks, including some with built-in intelligence.|
Smaller terminal blocks with built-in intelligence also are making inroads as alternatives to screw connection technology as standards evolve, says Sarah Stepanski, product manager, IEC terminal blocks, Rockwell Automation.
Short circuit ratings
Standards that affect terminal blocks continue to evolve, and one influential change involves short-circuit current ratings (SCCR) for industrial control panels. As states adopt changes made to the 2005 National Electric Code Article 409, Stepanski says industrial control panels need to be marked with a short-circuit current rating.
“Since this rating can be determined by a test of the system or based on the short-circuit current rating of each component in the power circuit, the ratings for terminal blocks are in the spotlight, she says. Unless otherwise documented, the assumed maximum short-circuit current rating for terminal blocks is 10 kA. Many customers are looking to achieve overall system ratings between 25 kA and 100 kA, so this assumed rating may be a limiting factor,” she adds. Testing and documentation of terminal block ratings can help, she adds.
EN and DIN standards for high-temperature fluctuations, vibration, and corrosion also are important benchmarks, says Phoenix Contact’s Freeland.
|Wago’s Power Cage Clamp (PCC) terminal blocks offer one-twist terminations, reducing install times and operator strain.|
Accommodation for larger conductors is another trend. Wago ’s terminal blocks with Wago Cage Clamps now run the gamut in sizes, says Michelle Goeman, product manager for terminal blocks and electronic interface, and usability has improved. Wago’s Power Cage Clamp (PCC) terminal blocks, for example, offer one-twist terminations, reducing install times and operator strain, she says.
Tighter connections for larger conductors help with variable frequency drives (VFDs) and motor controls, Goeman says, where the leading cause of failure is a result of loose connections. VFDs are not well served by screw-style terminal blocks, which are not inherently vibration proof and loosen with temperature cycling. “A major VFD manufacturer switched to PCC blocks instead of screw-style blocks in their VFD panels after having to re-torque the screw-style blocks before leaving the factory after validation testing,” she says.
Integration of various industrial networks and better engineering enables ease of use, along with better use of space, suggested Robb Black, vice president, Turck Network and Interface Division. “Our experience has allowed us to evaluate our customers’ specific needs for each of these networks.”
For instance, the Turck JRBS junction brick “was designed to meet customer demands in an easy-to-engineer package,” he says. The bricks simplify installation “while utilizing proven circuit design installed in thousands of Turck junction bricks currently in the field.” Black said development of this product resulted from evaluation of customer applications and requests.
Terminal blocks: Resources, application advice, products
Learning resources, application advice and terminal block product information follows.
Videos and more details
More on Phoenix Contact SPTA, a compact, low profile, angled terminal block that provides space-saving connections for up to 10 A.
E-learning on the Wago Cage Clamp Spring Pressure Connection Technology.
Wago Power Cage Clamp (PPC) system overview , variants, and more information.
|Mark T. Hoske, editor in chief , Control Engineering, can be reached at MHoske@cfemedia.com .|
Vertical mount junction bricks ease installations
Turck JRBS junction bricks for FOUNDATION fieldbus provide quick and easy connection of multiple devices to the main fieldbus trunk.
|Turck JRBS junction bricks for FOUNDATION fieldbus have 4, 6, 8, 10 or 12 ports and feature removable terminals for simple, efficient installation and wiring modification in tight spaces.|
JRBS junction bricks are available with 4, 6, 8, 10 or 12 ports and feature removable terminals for simple, efficient installation and wiring modification in tight spaces. These terminals are located on both sides of the brick to enable easy access for wiring from either direction—and they securely screw (or clamp) into place—eliminating the risk of becoming disconnected in high vibration environments. They can be DIN-mounted vertically or horizontally.
JRBS junction bricks provide short circuit protection for all ports, as well as visual status with bright LED indicators located on each spur. This allows devices to be added and removed without disruption to the network. An optional overmolded, pluggable terminating resistor also is available for use with the three pole terminal blocks.
Applications include oil and gas, petrochemical, power generation and distribution, pharmaceutical, water processing and management. The bricks have IP20-rated housing and hazardous location approvals. www.turck.us