Trends in Terminal Blocks

Contestants will be judged on originality and aptness of thought. Neatness counts! These may sound like rules for an essay contest but they also apply to control system wiring. In no other area of industrial endeavor does having the right devices assembled the right way make the difference between a well-executed and maintainable system and a confusing mess. According to Erich Langhorst, project manager at Bay Area Instrument & Electric (Benicia, Calif.) DIN rail-mounted terminal blocks came along at the right time to become almost the ‘defacto’ standard for panel building. ‘DIN-rail blocks save space and are extremely flexible. They are cheaper, quicker to mount, and offer a wide choice functions. Once DIN-rail blocks became widely available, the choice to use them vs. terminal strips and discrete components became a foregone conclusion for many control panel builders,’ Mr. Langhorst adds, ‘I counted myself among them.’

In its most recent examination of terminal block technology, Control Engineering polled 10,000 readers by email, which yielded 531 replies or a response rate of over 5%. CE’s readers rated availability, ease of installation, and cost in that order at the top of product selection criteria. For a product that may be required in the hundreds, thousands, and often tens of thousands in an industrial control system, this response is not unexpected. However, it is the next two responses from those voting ‘most important’ on these criteria that tell the tale.

What users need is important

Specifications and availability of a wide variety of special blocks is what allows users to apply originality and aptness of thought to the required system wiring. Thirty-six and 31% of those answering this question, respectively, saw these criteria as very important. And if the right amount and type(s) of terminal blocks are available at the right price, wiring neatness goes along for the ride.

The specialty blocks mentioned in the survey covered a wide variety of functions. Part the reasoning for including other required electrical/ electronic functions in the blocks goes back to good design practice. Consolidation not only saves valuable plant ‘real estate’- smaller and fewer components mean smaller enclosures-but also eliminates the need for separately wired components, saving both labor and material. Placing additional required electrical components in the blocks when possible also puts them in a central location, a definite advantage in system troubleshooting.

According to Larry Freeland, product manager, terminal blocks at Phoenix Contact (Harrisburg, Pa.) specialty blocks do not represent the majority in a terminal block population in an average control system. ‘In the case of fuse blocks, they exist roughly in a ratio of 1/7 with standard feed-through ones,’ Mr. Freeland says.

‘In the case of other specialty blocks adding extra functionality can be application specific. These blocks can be much more expensive than the standard items, depending on the specifications required,’ Mr. Freeland adds.

Specialty blocks can take replace much larger components, allowing panel space requirements to shrink drastically. These devices are functional replacements for many traditional control components, such as power supplies, signal conditioning modules, control relays, etc. These commercially available terminal block-style devices can also eliminate a significant amount of wiring, wire marking, and terminations on a ‘per panel’ basis.

When compared with a similar survey run a year earlier by CE, preferred termination method ranking remained the same with gains made in all technologies. Although both screwless (spring-type) and insulation displacement contact (IDC) technology have been around in practical form for at least 25 years, conventional screw-type blocks remain the most used by a wide margin over these technologies. In this survey, 95% of respondents said they use screw-type termination compared to 47% for screwless and a distant 22% for insulation displacement.

This compares to 77% for screw-type termination, 15% for screwless technology, and 4% for IDC type in the previous year. In both surveys, actual use values add up to more than 100% because of the multiple responses given. It is important to note that even though the ranking of the technologies has remained the same, the use of both screwless and IDC blocks have made gains in the field.

Jim Bachle, electrical products manager at Wago (Germantown, Wis.), feels that the slower acceptance of newer termination technologies has suffered because panel building often does not get the engineering attention that other control subsystems do.

‘Terminal blocks are a small percentage of the cost of an overall system and, as such, are not always fully investigated during the design process. Cost of maintenance and production downtime also figure into the life-cycle cost of terminal blocks. It is no longer acceptable to ignore technology advances is this area of the overall control system,’ Mr. Bachle comments.

Expanded terminal block offering

Milwaukee, Wis.- Rockwell Automation has expanded its line of Allen-Bradley QuickClamp terminal blocks with a series of timesaving enhancements and wiring accessories. Designed to simplify routine wiring installation and increase connection reliability, these enhancements address electrical isolation, connection of low-gauge wires, and replication of plotting schemes. Options include lower gauge wire capability, multiple terminal grounding, and high arm fuse blocks. New accessories such as test plugs and separator plates have also been added. www.rockwellautomation.com Rockwell Automation Response Center

Triple-level terminals

Cumming, Ga.- AutomationDirect offers a full line of DIN rail-mounted terminal blocks including a triple-level family. The triple-level terminal blocks include a feed through block for high-density wiring, a sensor block for sensor power and signal connections, and a sensor block with either PNP or NPN LED circuit-status indicator. The compact 5-mm thick design allows efficient use of panel space. The triple level family is rated for 300 V, 16 A, 26-12 AWG wiring, and carries UL/CSA/CE approvals. automationdirect.com AutomationDirect.com

Spring-clip termination

Palatine, Ill. – Spring-clip termination in the Telemechaniqe AB1 terminal blocks from Square D/Schneider Electric can reduce installation time by 50%. The IEC-type terminal blocks are available in seven different colors, making them easier for wire tracing. AB1 has 96 models, which makes it suitable for a wider range of applications. www.squared.com Square D/Schneider Electric

No tools required

Harrisburg, Pa.- Tyco Electronics Corp. has announced the Pivot Block terminal block, part of the Buchanan brand, which does not require tools or wire stripping to terminate wires. The product uses insulation displacement contacts (IDC) that eliminate the need for wire stripping and crimping. Furthermore, the tool-less design allows users to terminate wires by simply pivoting a lever on the terminal block, which forces the wire into the contact. The device provides a snap and tactile feel when wires are properly terminated. Contacts are available in 2-16 positions and accept solid and stranded wire from 22 to 24 AWG. www.tycoelectronics.com Tyco Electronics

DeviceNet-compatible terminal block

Irving, Tex.- Entrelec has introduced a ‘brick’ style remote I/O terminal block that is compatible with DeviceNet bus systems. The RIO system comprises a terminal block base module plus a plug-in DeviceNet electronic module. Terminal strips on the base module accommodate 2- or 3-wire field devices. Each RIO terminal block module includes eight digital inputs and eight digital outputs. Additional I/O points can be added with analog and digital expansion-module terminal blocks. RIO terminal blocks measure 4.02-in. wide x 4.41-in. high x 3.07-in. deep. www.entrelec.com . Entrelec

Current-monitoring modules

Richmond, Va.- Weidmuller, offers the WAVEcontrol Series of current-monitoring modules. They are available with either screw or tension-clamp connections. Through constant monitoring of devices and plant components, these modules can identify differences or interruptions that occur in electrical circuits, allowing specific measures to be taken to remedy the problems. WAVEcontrol modules can measure alternating or direct currents and can be used to monitor lighting, emergency lighting, heating elements, and motors in a wide range of applications. Available outputs include relay contacts or standard signals of 4-20 mA or 0-10 V. www.weidmuller.com Weidmuller Inc.

Terminal block have removable plugs

Harrisburg, Pa.- Phoenix Contact has introduced a pluggable system for its ST spring-cage terminal block series. New ST-COMBI terminal block features plug-in contacts. A 2.5-mm2conductor can be plugged into a 5.2-mm wide block with an IEC rating of 24 A and 500 V. In addition, the contacts in the terminal block and the plug connector are touch proof, making it easy and quick to connect. All original features of its developer’s spring-cage terminal block series have been integrated into this plug-in system. www.phoenixcon.com Phoenix Contact Inc.

Compact sensor blocks

Germantown, Wis.- Series 270 terminal blocks are intended for use in control panels and junction boxes where space is limited and persistent vibration is present. According to the developer, front-entry wiring makes the assembly easier and the original Cage Clamp connection for conductors guarantees a vibration-proof connection. Blocks feature a jumper system for the power supply. Jumpers are available in 2-way through 17-way versions for power distribution. An optional LED for status indication and three locations for marker cards per terminal block offer assurance of a secure connection. www.wago.com Wago

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