Abstract: Electronic control apparatus of a kind used in low voltage industrial equipment such as assemblies of motors or circuit breakers. Where an overall controller, e.g. a programmable logic controller (PLC) controls an array of (e.g.) motors (M1, M2, M3) by way of respective control units (13, 23, 33) identification or location of selected motors is usually effected by an address stored in the respective control unit. A faulty control unit entails replacement and loss of the location address which has to be reentered as a skilled operation. The invention provides a separate non-volatile memory (15, 25, 35) for the location address, this memory being physically associated with the particular motor (M1, etc.). A replacement control unit (13, 23, 33) is automatically loaded with the location address which was retained.