The environmental conditions in which a machine will operate often influence the builder's choice of components. While a corrosive environment might dictate the use of an alloy metal, the need for such precautions often stems from the protection that is provided for the components.
Terminal blocks, for example, are available in many varieties, but many machine builders don't let the environment scare them away from their preferred terminal-block choice.
"We manufacture a line of standard and custom solutions for liquid filling and packaging lines," says Jack Chopper, chief electrical engineer at Filamatic (www.filamatic.com) in Baltimore. "Our customer base includes pharmaceutical, medical, diagnostic, biotech, cosmetic, personal care, food and beverage, household products, chemical specialties and contract packagers. Unless the application dictates a specific material—thermocouples and RTDs are good examples—we usually use the same high-quality screw-type terminal blocks rated for pollution degree 3 no matter what the conditions or environments are."
Filamatic always houses the terminal blocks and the related connection points in a high-quality enclosure that is suitable for the intended environment, explains Chopper. "It has been our experience that it is far more robust to use high quality terminals and protect those terminals than it is to find terminals that survive the aggressive environments when exposed," he says.
Many machine builders agree.
"We don't have any environmental conditions to worry about with our terminal blocks," says Steve Corwine, vice president, customer support, at CBW Automation (www.cbwautomation.com) in Fort Collins, Colorado. "All of them are enclosed in NEMA 12-rated boxes in clean plants for food packaging."
Joe Bowen, senior engineer at FMC Technologies (www.fmcti.com) in North Salt Lake, Utah, explains, "The terminal blocks we choose are generally cage-clamp or screw-type, and environmental conditions don't play a significant factor."
Joe Roegner, SCADA technician for Orange County (www.ocfl.net) in Orlando, Florida, explains that his organization sticks with the contractor's choice. "As far as the environment goes, it's very important to keep out H2S gases and moisture," he says. "I've seen nice panels damaged in less than a year by H2S gases and moisture coming into the panel from a sewage lift station."
Environmental conditions primarily affect the terminal-block selection when the enclosures that house terminals are directly exposed to harsh environments, explains Carlus Hicks, marketing manager—North America, Weidmüller (www.weidmuller.com). "High acidic or corrosive environments, such as constant salt spray or acidic agents from food processing exposure, require terminals with a clamping system that has high nickel-alloy or a stainless steel makeup to offer the best performance in terms of longevity and consistent electrical connections," he says. "High-temperature or fire-rated environments that normally exceed 200 °C would dictate the selection of terminals molded in ceramic material with a nickel-plated contact system that has an overall temperature range of 250–750 °C."
For machine builders shipping equipment, insulation displacement connections (IDC) and spring-cage terminal blocks provide secure connections even as equipment shifts, whereas screw-type connections require torque testing to ensure secure connections before installation of the machine, explains Jacob Feutz, marketing specialist at Eaton (www.eaton.com). "Hybrid terminal blocks are typically employed when panel or machine builders need a vibration-resistant connection on one side of the terminal block and a simple screw connection on the other for field installation."
A vibration-prone environment, common to all types of machinery, can cause some screw terminations to loosen over time, warns Bruce Burroughs, business development manager at Wieland (www.wielandinc.com). "This can be prevented with certain design features that counterbalance the effects of vibration, as well as other dynamic forces, such as temperature," he explains. "These design features include brakes molded into the insulating housing and formed in the clamping body, which both capture and keep the screw from backing out. Also, the design of the cage-clamping body, if it is stamped and folded as opposed to extruded, can prevent the screw from backing out. The fold of the clamping body can act as a brake on the screw. Alternatively, the screwless spring clamp is ideally suited for vibration-prone environments, due to its constant force on the conductor."
A highly corrosive atmosphere, such as wastewater treatment, is ideal for the extruded clamping body, as there are no bends or folds for corrosion to attack, says Burroughs. The clamping body, whether extruded or stamped and folded, should be of nickel-plated copper alloy, and the screw should be of similar metal.
"Connection reliability can't be determined by the presence or absence of visual corrosion," explains Sarah Stepanski, global product manager, terminal blocks & marking solutions, Rockwell Automation (www.rockwellautomation.com). "A well-designed terminal clamp will have a gas-tight seal protecting the electrical connection from corrosion. In some cases, the electrical performance will continue to function normally even after severe corrosion can be seen on the terminal."