Electrical & Electronic
3-2002 It's so simple
Problem: It is generally acknowledged that the best way to ensure good
electrical contact with an earthing strip or rail is to use some kind of grub screw and to
do it up tight.
If used to attach a terminal block, the usual result of over tightening is to distort the mounting rail and/ or cause the block to lean. Doing up screws also takes time, and requires space both to accommodate the length of the screw in its unscrewed condition and an aperture to allow insertion of a screwdriver.
Solution: Designers at Weidmuller have come up with a clip arrangement that earths at least as well as a screw without any of the disadvantages.
In this design, the whole width of the block is used as the clip and slid onto the edge
of the rail on one side. A protrusion is formed on the earthing strip in the block on this
side. The block is then swung round so that the cam shape on the other side of the block
locks onto the other side of the rail. The holding force of the cam is multiplied by a
factor of more than ten by the consequent lever action to apply a large contact force on
the protrusion on the other side.
The consequence of this is that adequate contact force is guaranteed while it is impossible to apply excessive screw force sufficient to distort the rail and cause the block to lean. Installation is greatly speeded up and the block height halved by eliminating the space required for a screw and access to it by a screwdriver.
Applications: The design concept has been applied to Weidmullers WPE 4N blocks but is expected to be applied to other products. And the same principles can be applied to any products needing to be attached to and earthed by a rail. TS