Periodic inspection of portable earthing and short-circuiting devices
June 2015
Electrical Power & Protection
An important measure when working on electrical installations, according to the five safety rules of DIN VDE 0105 - 100, is the fourth rule: “Carry out earthing and short-circuiting”. This ensures that the installation is dead while work is carried out. However, every protection measure is only as safe as the tools that are used.
Reduced cable cross-sections of portable earthing and short-circuiting devices (EaS devices) resulting from copper corrosion and breakage of conductor strands, or increased resistances in the connections, may have fatal consequences when earthing and short-circuiting devices are subjected to short-circuit currents. Therefore, portable EaS devices must be tested prior to each use and at regular intervals. So far, only a visual inspection made economic sense. However, a new procedure is now available which provides reliable information on the condition of the portable EaS device based on static and dynamic measurements of the ohmic resistance.
Dehn Africa offers this improved test for portable EaS devices on the customers’ premises.
An earthing and short-circuiting device is tested in three steps and the resistance values are compared with theoretically and experimentally determined limit values. The first step is the visual inspection for visible signs of damage. A static test is performed in the second step, in which the absolute resistance value is measured at the stationary earthing and short-circuiting device. Step three includes the dynamic test, which notes the measurement of the relative change in resistance at the moving earthing and short-circuiting device. The measurement of the resistance change value (R) between the non-moving and the moving EaS device is a new approach which allows for the detection of local damage, such as breakage of conductor strands in the conductor cable. The new test setup consists of a special micro-ohmmeter, a rail structure and the relevant software. Practical testing has shown that numerous earthing and short-circuiting devices tested are invisibly damaged. This damage could not be found by means of visual inspection alone, thus illustrating the importance of using the new procedures to test used EaS devices at regular intervals.
Safety devices and equipment from Dehn are manufactured and tested in line with the requirements of applicable standards. In addition to maintenance tests on earthing and short-circuiting devices, Dehn is also a reliable partner for maintenance tests on voltage detectors, switching sticks, fuse tongs, insulating sticks and earthing sticks.
For more information contact Alexis Barwise, Dehn Africa, +27 (0)11 704 1487, [email protected], www.dehn-africa.com
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