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By Wayne Labs, Contributing Editor
hile terminal blocks and connectors have always been essential in organizing wiring, the push is on to make faster connections, get them right the first time and to have them work reliably in all sorts of environments. Not all tubing and fittings have to work in nasty environments, but in many cases, they’re called upon to deliver some pretty nasty fluids. Here’s a brief update on connector technologies—for both electrons and fluids.
Screw, clamp, and IDC
IEC terminal blocks are available in three basic types. Knowing when and where to use each type can save costly revisits by maintenance technicians. Screw terminal blocks have been around forever, and typically accept as many as four terminations per block. Spring-clamp blocks require stripping the insulation—as do screw types—and they are generally 30–50% faster to wire than screw types. The newest type, insulation displacement technology (IDC), requires no stripping of insulation and works with solid and stranded wire, but there is a limit to maximum wire size and types of compatible insulation.
Screw terminal blocks might seem the ideal solution for any application. But PCK Refinery GmbH, which processes over 10 million tons of raw oil a year in Schwedt, Germany, found screw terminal blocks a liability. “Every few weeks, screw-type terminal blocks would have problems because of loose screws due to equipment vibrations,” says Christian Rada, head of PCK’s electro-technical maintenance. PCK is now specifying Wago Cage Clamps for the control equipment.” In response to this problem, however, most vendors provide screw terminal blocks with self-locking screws, which will probably solve many of these application problems.
Pluggable Jumpering Saves Time
According to Carlus Hicks, North American product manager for terminal blocks at WeidmĂ¼ller, pluggable jumpering is not a new idea to spring-clamp and IDC blocks, but when combined with traditional screw clamp blocks, the result—which replaces wire jumpers—is fairly new and can save users a lot of time. How much time can pluggable jumpers save? Brian Delfosse, IEC terminal block manager at Rockwell Automation says, “It used to be that everybody used screw center jumpers, and it took forever to install them. And if the installer made a mistake, he had to unscrew every jumper wire and slide them all left or right to the correct position and then screw them all down again. But with pluggable center jumpers, you can plug in about 30 poles in two seconds vs. about 20 minutes installation time to tighten down 30 screws for a screw jumper wire.”
One industry trend today is to merge the various connection technologies together side-by-side in a single rail. “Today’s customer is seeing the need not to standardize on one [rail] technology,” says Phoenix Contact terminal block product manager, Larry Freeland.
“Customers are realizing that it’s better to let the application dictate what connection technology is most appropriate. Having a screw clamp, spring cage, auto-spring and IDC product in a single complete system allows the customer a choice to meet his demands for corrosion resistance, speed, clamping force, pull-out force, space, etc.”
Another important emerging trend, according to Delfosse, is to add functionality to terminal blocks, and many manufacturers have responded to customer demands with fuse blocks, relay blocks with snap-out relays, transient protection blocks, and plug-in capability for components such as resistors, capacitors, diodes and fuses. Double-level blocks add to the number of circuits a block can handle, and usually include a ground as well. “Troubleshooting is another key aspect of using terminal blocks,” adds Delfosse. “There are great troubleshooting solutions the terminal block industry is offering. They include test plugs, test probes, and test adapters—which allow a connection to an ammeter, voltmeter, or any test device.”
Get the Lead Out â€¦
The European Restriction of Hazardous Substances (RoHS) Directive of January 27, 2003 bans the use of certain substances in new electrical and electronic equipment put on the market after July 1, 2006 (exceptions for certain applications are listed in the Annex of the directive). The banned substances are lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyls (PBB) or polybrominated diphenyl ethers (PBDE). While this is not an issue in the U.S., Hicks notes that if vendors hope to sell connectors in Europe, the lead will have to come out from any solder (lead/tin) coatings that are currently used on connectors. In addition, hexavalent chromium, which protects against corrosion, is mainly used in the form of chromium layers, in particular on screw connection systems and mounting rails.
Connectors Assume New Roles
As fieldbuses proliferate, the need for connection systems that use junction boxes is displacing the traditional role of terminal blocks. This is not to say that terminal blocks can’t handle fieldbus systems, but for localized machinery or processes, cable, and connectors, junction boxes are a viable alternative. What Jim Masterson, vice president of Process Automation at Turck, sees are customers who want to convert from conduit and terminal blocks to quick-disconnect cabling wherever possible, especially for local runs.
According to Masterson, “We are [telling customers at process plants] that they can install in general purpose and Class I Div. 2 areas, properly-rated cabling and protected connectors to hook up all their field devices including transmitters, valves, switches, etc., if they follow the right guidelines, which are fairly new relative to the national electric codes.” This includes the use of open wiring up to 50 ft (either in trays or hanging in space) if the cable is rated crushproof and meets other guidelines, allowing it to be used outside of conduit.
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