applied to the power control system of an electronic computer with reference to the drawing there is shown a pair of input terminals 10 and 12 for receiving the ac line power the latter is applied via line filter 14 to the main circuit breaker 16 of the cabinet supply four relays are depicted in the drawing three of the relays are shown schematically as having a single coil and these are designated respectively ka kb and kc the last relay kc is assumed to be of the time delay variety another relay kd is of the latch in type and includes two coils designated respectively kdl for the 34 latch 34 function coil and kdr for the 34 reset 34 function coil when a given one of the coils is energized the relay contacts are mechanically latched in a predetermined state and will remain so even if the energization is removed on the other hand energization of the other coil causes the contacts to latch in the opposite state the pairs of switch contacts associated with each of the relays carries the appropriate coil notation plus a subscript reference numeral for example relay ka has four sets of contacts namely ka 1 ka 2 ka 3 and ka 4 the contacts are represented schematically as singlepole single throw spst switches and in accordance with how they are shown in the drawing that is either open or closed it is to be assumed that this is the normal condition of the contacts associated with an unenergized relay coil in the case of relay kd the contacts are shown in a 34 reset 34 state implying that the kd reset coil was last energized.