New-TechEurope Magazine | November 2017 | Digital Edition

Sensors Special Edition

Protecting man and machine against damaging residual currents

Peter-Lukas Genowitz, Eaton

How the correct choice of the residual current device ensures operator safety, machine uptime and profitability Introduction Technology continues to rapidly evolve, and machine builders are faced with designing products to enable their customers to produce faster, and more efficiently, at a lower cost. Product lifecycles are becoming shorter, placing demands on machine builders to design and develop highly customized machines. Exporting equipment remains complex, as electrical standards often differ from country to country. Manufacturers and their end users are looking more towards their suppliers for support, due in part to in-house engineering team size reductions. One aspect of this is electrical circuit protection, which can impact both safety and machine up-time. Electrical

faults can have devastating effects on the human body causing injury, and lead to machine failure and fire – affecting productivity. The function of a residual current device Residual currents in electrical systems are caused by either fault conditions or generated by system components such as frequency converters. The role of a residual current device (RCD) is to automatically disconnect the power supply if the fault can pose a risk. Residual currents can arise for many reasons and take many forms. The biggest challenge is being able to differentiate between all the possible forms of residual current, while protecting people and equipment, but on the other hand avoiding nuisance tripping related to system caused earth leakage currents. The solution is to recognise the different forms of

earth leakage current that can occur, and design in the appropriate RCD. Types of protection Devices have to shield operators and technicians from the dangers of electric current, both during normal use and fault conditions. Potentially life-threatening accidents can result from either direct or indirect contact. Direct contact refers to when a person touches a live electrical part that is intended to be live during normal operation. Indirect contact is a fault when a conductive, non-live exposed and touchable part becomes live due to an electrical fault. There are multiple types of protection required; basic, fault, additional and fire. Basic prevents contact with live parts through insulation or a cover. Fault protection includes situations where an insulator (basic protection) fails and the RCD switches off before dangerous voltages can occur on

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