Accessory network for an electronic trip unit

An electronic trip unit (10) having a two-wire, asynchronous, serial communication accessory network (48) that is connected to a number of unique digital and analog remote slave devices (50,52,54 and 56). The address for each slave device is set by its function so that the trip unit (10) does not have to be programmed in the field each time an accessory is added to the system. The network (48) is capable of two-way communication when requested by the electronic trip unit (10). Accessory network communication is controlled by a first microprocessor (24) within the electronic trip unit (10) or alternatively by a network interface gateway (58). The first microprocessor (24) also controls overcurrent and instantaneous protection functions of the trip unit (10) while a second microprocessor (46) controls voltage based and metering functions. The second microprocessor (46) also has the capability of communicating with a central control network (38).