Abstract: An electromagnetic relay to be used in applications such as DC motor reversing. The relay consists of two electromagnetic devices in a single enclosure with contacts configured in a so-called "H-bridge" circuit. Each of the devices has a movable contact element, while both devices have a common pair of normally closed and normally open stationary contact elements. Both electromagnetic devices have coil bobbins which are preferably identical in shape and are locked together by means of the common stationary contact elements without a need of additional fastening means. In this manner, the number of parts is minimized and the amount of adjustment required is reduced.

Abstract: An improved ground monitoring circuit for detecting the integrity and proper connection of the ground conductors in an electrical cable of an electrical power distribution system of a type that is commonly used at a surface mining site. A complete conductive loop is established between the ground conductor, or conductors, and the ground check, or pilot wire of the cable. A sensing signal at a frequency higher than the power frequency is coupled onto the ground monitoring loop. The monitoring loop includes a terminating resistor of predetermined value. The sensing signal on the ground conductor in the loop is isolated from local ground by means of an impedance element that presents a high impedance at the sensing signal but not at the power frequency. The impedance element is connected between the ground conductor of the power cable and the local ground.