The test apparatus comprises a horizontally disposed beam, which is pivoted about its centre point. A short length of steel wire, 1 mm in diameter and bent into a U-shape, the base of the U being straight, is rigidly attached, at both ends, to one end of the beam, so that the straight part projects below the beam and is parallel to the axis of the beam pivot.
The plug is held by a suitable clamp in such a position that the straight part of the steel wire rests on the plug pin, perpendicular to it. The pin slopes downwards at an angle of 10° to the horizontal.
The beam is loaded so that the wire exerts a force of 4 N on the pin.
The plug is moved backwards and forwards in a horizontal direction in the plane of the axis of the beam, so that the wire rubs along the pin. The length of the pin thus abraded is approximately 9 mm, of which approximately 7 mm is over the insulating sleeve. The number of movements is 20 000 (10 000 in each direction) and the rate of operat