DIRAK has developed new grounding countersunk screws with segment cutting edge and scraping tooth, allowing for electrical and mechanical contact with metallic base materials without extensively pretreating them.
Potential equalisation is generally used to protect persons and equipment against electric shocks due to overvoltage. However, painted or powder coated metallic base materials cannot be used without pretreatment of the points that connect into the potential equalisation. If conventional fastening elements are used, the upper layer of the contact surface must first be removed or kept free of paint. DIRAK GmbH points out its new grounding countersunk screw eliminates this time and cost intensive step.
Georg Hübner, senior product trainer at DIRAK, explains: “The advancement of the segment cutting edge and scraping tooth under the screw head allows for electrical and mechanical contact with metallic base materials without extensively pretreating them. The grounding countersunk screws establish potential equalisation either in a counterbore or in a cylindrical borehole.”
In a counterbore the segment cutting edge is responsible for the electrical contact with the metallic base material. “The double-sided design of the segment cutting edge guarantees reliable potential equalisation. Cutting through the layer of paint up to a maximum 170µm does not produce any paint chips,” explains Georg Hübner. The segment cutting edge and scratch tooth increase the underhead friction in both a counterbore and a cylindrical bore, thereby improving the protection of the screw against coming loose in the connection.
In a cylindrical bore the double-sided scraping teeth, which are offset by 90°, are responsible for ensuring reliable potential equalisation on the edge of the metal sheet. As the screw is turned in, they scratch the painted edge of the hole free to a maximum depth of 170μm and thus make electrical contact with the metal. The purpose of the segment cutting edge is to centre the screw in the hole.
DIRAK offers the M6 x 12 grounding countersunk screw with a standardised metric thread and in a second variant with a metric self-tapping thread. “This screw cuts its own thread in a borehole. It is designed with a slightly conical structure to make it easier to find the borehole and centre the screw in it.” Both variants are tested in accordance with DIN EN 61439-1 (VDE 0660 part 600): 2012-06 ‘Low Voltage Switchgear Combinations’.
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