British Post Office Modular Dc Power Plant

In the mid 1970s the British Post Office developed a new modular d.c. power plant system as the standard source of power at -50 volts for all new telecommunications installations except those in the smallest rural exchanges. The plaint employs a simple and unique form of end-cell switching. Some 500 plants have now been commissioned and there have been 2000 successful plant-years of operation.