Shrinking in size but not out of sight

An old proverb states a little body often harbors a great soul. The same may be said for the tiny, and oft overlooked terminal block. But, "Like any other control, in order to save money, users need to reduce panel and enclosure sizes, especially if they're custom made," says John Nussbaum, staff marketing engineer for Square D (Palatine, Ill.

By Michael Drakulich, assistant editor June 1, 1999
Trends in Terminal Blocks
  • Screw-type termination

  • 4-20 mA and Ethernet communication

  • Availability and ease of installation

An old proverb states a little body often harbors a great soul. The same may be said for the tiny, and oft overlooked terminal block. But, ‘Like any other control, in order to save money, users need to reduce panel and enclosure sizes, especially if they’re custom made,’ says John Nussbaum, staff marketing engineer for Square D (Palatine, Ill.). With terminal block design following the industrial paradigm of smaller size and increased functionality, this plant-floor workhorse still carries a mighty load.

Control Engineering ‘s new study takes a look at trends in the current terminal block market. Fifteen hundred CE readers were polled at random regarding use of terminal blocks. Three hundred seventy-eight filled out the survey questionnaire for a response rate of 25%. In all, 94% of the respondents specify, recommend, and/or buy terminal blocks. Of those 94%, 61% specify, recommend, and/or buy terminal blocks for in-plant requirements; 19% do it for OEM (resale) requirements; and 14% do it for both in-plant and OEM requirements.

Among the industry segments represented by the survey respondents, raw materials processing comes out on top. Forty-seven percent of the respondents say their company’s primary end product is raw materials. Manufacturers of machinery and equipment for manufacturing and services industries come in a distant second place with 16.3%. Instrumentation and control equipment manufacturers accounted for 10.4% of the survey’s respondents, while 6.2% say their company’s primary end product is other fabricated metal and miscellaneous manufacturing.


Screw-clamps have been used for electrical termination almost as long as electricity has been harnessed for commercial and industrial use, and screw-clamp terminal blocks are still the favorite among this survey’s respondents. The survey says nine out of ten respondents still use them despite the availability of other, more advanced types. Following in a distant second place are screwless terminal blocks, which are used in 21% of respondents’ applications. Prewired blocks account for 14% of the votes, while insulation displacement blocks are found in 11% of respondents plants (results exceed 100% due to multiple responses).

Engineers often find themselves using instruments and devices that were selected by others, but not necessarily the type they prefer. In this case however, the type of terminal block employed most and preferred most are the same. Nearly two-thirds (65%) of the survey’s respondents actually prefer to use screw-clamp terminal blocks over any other type. Twelve percent prefer screwless, 7% would like to use prewired, and 2% like the insulation-displacement type. Fourteen percent indicated no preference at all.

Square D’s Mr. Nussbaum says despite the numbers, the presence of screwless terminal blocks is growing. Part of the reason, he stresses, is Wago (Brown Deer, Wis.) let its patent for the screwless terminal block expire. ‘That patent eliminated companies from getting into the screwless terminal block market. Now it [the market] is open to everyone.’

Jerry Scrignoli, terminal block product marketing manager for Phoenix Contact (Harrisburg, Pa.) says a potential problem that may convince users to buy screw clamp over spring clamp terminal blocks is the actual force the spring puts on the wire. Spring clamps put ‘only about one tenth the force of a screw clamp,’ he says, which makes connections using large wire, and those in high-vibration areas, susceptible to loosening. For normal, low-voltage applications with small-to-average sized wire, he says spring-clamp terminal blocks perform just as well as their screw clamp counterparts.

Screws are quicker than clamps

Mr. Scrignoli says manufacturers of screwless blocks tout quick installation time as an advantage over screw-type blocks, but the difference may be lost on most users.

Mr. Scrignoli’s company, Phoenix Contact, makes both types of blocks. In a demonstration to determine installation time savings, they formed 10 teams from different U.S. sales districts to wire a simple assembly. Five teams used screw clamp blocks, five used screwless blocks. Each team had to wire a proximity sensor, a power supply, and a buzzer in a series. Once the wiring was complete, and the buzzer went off when the sensor detected the intended object, the team was done. The first five teams to finish all used screw-type blocks. He says it’s because the industry has been working with these type of terminals for so long. ‘Everyone in the industry is familiar with screw-type terminal blocks. The time users can save with screwless terminal blocks won’t be realized until they become comfortable installing them, and even then the time saved is marginal.’

Respondents are almost split down the middle when asked if they use board-mounted connectors. Fifty-three percent say ‘yes,’ 47% percent say ‘no.’ The 53% percent that answered yes were then asked how important closer pin spacing is compared to what is currently available. Eleven percent say it’s very important and 40% say it’s somewhat important. Twenty-nine percent say closer pin spacing is neither important nor unimportant, while 16% say it’s somewhat important or not important at all.

Communication methods

Respondents to the survey use more than one communication protocol in many cases. Due to these multiple responses, results exceeded 100% when the survey asked what protocol respondents use, or plan to use in the next 12 months. The 4-20 mA signal is used most, with Ethernet following closely with 33.3% and 26.2% of the votes respectively. DeviceNet is the only other protocol that received more than 10% of the vote (11.9%). Following DeviceNet are ControlNet (9.5%), FOUNDATION fieldbus (9.5%), HART (7.1%), and Profibus (7.1%).

Also, 4-20 mA is the top vote-getter for the respondents who will add communication protocols in the next 12 months with 16.7%. Following closely behind are DeviceNet with 14.3%, and Profibus with 12%. Next is HART, which 9.5% of the respondents will add to their terminal block applications. Other protocols mentioned are ControlNet (4.8%), Ethernet (2.4%), FOUNDATION Fieldbus (2.4%), and SDS (2.4%).

What will you buy?

Compared to 1998, purchasing of terminal blocks for the next 12 months looks good. The majority (58%) say that their purchases will at least be the same as in 1998; 22% say purchases for their companies will increase; while 8% say terminal block purchases will decrease. Eleven percent are not sure what terminal block purchases will be like for their companies in the next year, while 1% have no answer.

Asked what characteristics are most important when buying terminal blocks, respondents say availability and ease of installation are most important, followed by specifications, cost, and variety of special blocks (see graph).

Keith Cumiskey, product manager for Rockwell Automation (Milwaukee, Wis.) agrees with the statistics. He says most customers need a broad line of products, but orders heavily favor blocks that aren’t required to perform highly specialized functions. ‘Ninety percent of the terminal blocks customers order are very simple. The remaining 10% are specialized. Those specialized blocks may have more terminals or come in different colors for easy visual indication.’ Specialty blocks, he says, also can have ‘fuses in them, or dual circuits to save rail space.’

The statistics support Mr. Cumiskey’s views. Fuse-type terminal blocks are the top vote getter among the specialty terminal blocks respondents use, garnering 81% of the votes. Circuit breakers, relays, and input blocks all vied closely for the second spot with 54%, 53%, and 49%, respectively. Surge suppressors follow at 25.6% and resistors come in with 20% (results exceed 100% due to multiple responses).

In the respondents’ estimation, over the last five years terminal block density (size, spacing) is the one characteristic that has changed the most. Ease of installation and use is the second most popular opinion, followed by compatibility, variety and versatility, and screwless termination.

While size and spacing may be the most recognizable change in terminal blocks over the last five years, their flexibility and functionality are becoming inversely proportional. Users need a variety of types to choose from, need them to be versatile, and need them to be a ‘fit-and-forget’ solution; all in a neat little package designed to save rail space. That’s quite a bit to want in a product, but the worth of a thing is best known by the want of it.

Terminal block products

For more information on terminal blocks, visit .

Quick termination

Harrisburg, Pa.- Quix modular terminal blocks have been designed to save users up to 60% of installation time. Users make connections with a lever motion of a screwdriver and inserting the unstripped wire (up to 1.5 mm2, # 20-16 AWG). Strain relief ribs within the housing and a special snap fitting in the terminal block metal body ensure a permanent gas-tight and vibration-resistant connection. The Quix series also features a screwless jumper system that simply snaps in place. Quix terminal blocks are front loading and equipped with integrated test connection.

Phoenix Contact

Process control terminal block

Burgaw, N.C.- Sensor Block is crafted specifically for termination of actuators and initiators in process control applications. The terminal block incorporates a mounting base designed to accommodate 8 (45 mm wide), or 16 to 17 (90 mm wide) I/O points. The base module has room for a power supply terminal which uses the integrated bus bar to distribute excitation/supply voltage to adjacent I/O points. The mounting base can be either DIN-rail or panel mounted. A spring clamp, top entry wiring system is said to make wiring easier, along with color coding of positive, negative, and shield connections.

Wieland Electric

High-current PCB blocks

Brown Deer, Wis.- Wago’s high current PCB terminal blocks are equipped with the Wago Cage Clamp connection and have small dimensions despite being capable of connecting 4 mm2or 6 mm2conductors. The 4 mm2version, with a rated current of 20 A, is available with a pin spacing of 5 mm and a nominal voltage range up to 250. The 6 mm2version, with a rated current of 32 A, is available with pin spacings of 7.5 and 10 mm. Two solder pins per pole ensure the terminal block is firmly fixed to the PCB. Snap-on type fixing flanges provide more safety when the terminal block is highly stressed.


DeviceNet junction boxes

Schaumburg, Ill.- DRT1 series DeviceNet Junction I/O blocks connect photoelectric sensors, proximity sensors, or actuators to a DeviceNet network. Available in eight input, eight output or mixed eight in/eight out models, these junction boxes conform to IP66 standards. They can also be mounted directly into harsh environments without need for an additional enclosure. Installation is easy with its standard connectors. No tools are needed.


Prewired terminal block

Palatine, Ill.- Telemechanique Telefast 2 reduces wiring time and cost by replacing multiple wires with a single prewired cable. The Telefast 2 system also reduces panel space requirements, provides I/O protection, contact amplification, and increased marking area. Available in modular units with 8-, 12-, or 16-channel configurations, the Telefast 2 system connects to most PLCs with high density cards. Telefast 2 modules have I/O signal applications for discrete logic signal inputs, solid-state relay inputs and outputs, electromechanical relay outputs and analog signals. The solid-state and electromechanical relay output modules are available with either printed-circuit-board mounted relays or plug-in relays.

Square D

Remote digital I/O

Irving, Tex.- RIO (Remote I/O) terminal block module features a building block concept for remote bus interface and distributed intelligence. The RIO module is comprised of a terminal block base module and a selectable bus dependent, plug-in module. RIO is compatible with Profibus DP, Interbus, and WorldFIP. Terminal strips on the terminal block module accommodate two- or three-wire field devices such as sensors and actuators. Each electronic bus module includes eight digital inputs and outputs. Additional I/O points may be added with expansion modules that come in increments of 8 inputs/8 outputs, 16 digital inputs, or 16 digital outputs. The plug-in concept allows the bus system to be changed without rewiring the terminal block base module.


Open, connect, and go

Alpharetta, Ga.- 8WA2 screwless terminal blocks from Siemens Energy & Automation employ cage clamp terminals for fast, easy installation. Users simply insert the small assembly tool included with the 8WA2 to open the selected terminal, insert the wire in the proper opening, then remove the tool for a safe, permanent connection. No end sleeves are required thanks to the front connection, and the length of insulation to be stripped is printed on the housing. 8WA2 terminal blocks come in three form factors: a basic two-tier, through-type terminal, a three-tier terminal for commercial or institutional buildings, and an initiator/actuator version for connecting switches and sensors to a PLC.

Siemens Energy & Automation

Convenience without screws

Milwaukee, Wis.- QuickClamp IEC screwless terminal block features a spring clamp to secure wires, eliminating the time-consuming task of screwing down each wire. The screwless design requires less maintenance and installs easily with a flathead screwdriver. To ease circuit identification, a variety of snap markers are available in blank, preprinted, or custom-printed formats for all QuickClamp models. An interlocking block feature allows users to simply remove QuickClamp block from the rail. Available in seven models, Quick Clamp can be used in a wide variety of wiring applications, from I/O wiring for PLCs, to low-level power circuits for contactors.

Rockwell Automation/Allen-Bradley

Color coding for easy ID

Cumming, Ga.- DINnectors terminal blocks come in seven colors for easy identification of circuits: red, yellow, orange, blue, green, gray, and black. Users can code by circuit type, voltage, or current. These UL, CSA, and CE-approved 600 V, 30 A multicolored blocks are available in 18-10 AWG terminal size. The DINnectors product line features several connector styles: feed through, multi-level, ground, fuse, disconnect, and mini. These blocks feature finger-safe moldings as well as self-locking, vibration, and corrosion-resistant clamping systems equipped with captive screws to help ensure fast, safe, and reliable connection.

Streamline DeviceNet connections

Columbus, O.- Cutler-Hammer’s DN50 I/O blocks are used as stand-alone I/O blocks in conjunction with DeviceNet. When connected to the network, the DN50 allows devices without a CAN (Controller Area Network) communications chip to communicate through the DN50’s I/O points. Programming and configuration can be done with NetSolver and NetView software packages. This enables users to troubleshoot, set attributes, and gather diagnostic information quickly and easily through the system’s industrial PC or PLC. This block allows additional DN50 expander modules for installing additional I/O points, and is expandable from 14 to 56 I/O. It’s also configurable via the DeviceNet master PC.


Field-configurable signal conditioner

Richmond, Va.- UPAC family of single point conditioners offer configuration selector switches, enabling users to change the signal conditioner as processes change in the field. Eleven modules are available, all able to handle multiple input/output combinations. With their setpoint control configuration, UPAC modules can be used as controller for small, dedicated applications such as mixing and temperature control. The modules compact size allow them to fit in field junction boxes, and they have a built-in power supply with a range of inputs, providing three-port isolation for signals.