The point machine and the point heating operate in cycles controlled by time and temperature, at the end of long supply lines, in changing weather. The SK 7817N/200 time relay of the MULTITIMER family provides delays, pulses and cycles in one module with eight functions, supplied from a wide range of AC and DC voltages, with a classification to EN 50155 in its datasheet.
Point heaters and loads with high switching frequencies are handled by POWERSWITCH solid-state switches: relays for mounting on a cooling plate and contactors with a matched heat sink for DIN rail, in versions for resistive loads with zero-crossing switching and with load current monitoring, which detects a burnt-out heater. Interlocking circuits of the point machine control use the OA 5603/39 PCB relays to EN 50578.
Selection of a solid-state switch requires checking the load current against the derating curve at the cabinet temperature, the peak blocking voltage against overvoltages in the network, and protection with a semiconductor fuse.
At drives with three-phase motors the RN 9877 phase monitor checks phase sequence, phase failure and asymmetry without a separate auxiliary voltage.
