In a number of applications, networked systems require distribution of both power and data signals to and from any number of devices. For example, in industrial applications, a networked system may distribute power, typically three-phase power, as well as appropriate data signals to any number of locations. In traditional systems, power and data signals are transmitted over discrete wiring pathways. That is, power is distributed over dedicated power wires and data is distributed over dedicated data wires, both of which are disposed in separate protective conduits or cable jackets tubing.
By way of example, networked control for a motor may require three wires for the transmission of three-phase power, one or more wires for a second level of power, an earth ground wire for coupling to ground, a neutral wire for return power signals and a pair of data wires for the communication of data signals. Thus, a traditional system may require nine or more discrete wires for operation. Some systems also use a further conductor for override or emergency data communication. In turn, this may lead to increased costs with respect to both manufacturing and installation. Moreover, the large number of conductors required increases the likelihood of a problem, such as a short, occurring in one of the wires. This too may increase costs, particularly maintenance costs.
In more complex systems, power and data signals may be distributed to and from any number of devices, sensors and control circuits all working in cooperation. Accordingly, the system may be interconnected with trunk cables and branch cables extending from the trunk cables by conductors which serve as tapping junctions to the branch cables. However, in many traditional networks, if an electrically upstream device is brought out of operation, then the electrically downstream devices, although functioning properly, may also be brought out of operation. This may lead to undesired downtimes where repair perturbs overall operation of the entire installation. Thus, it would be advantageous to independently interrupt power to the various components of such systems.
Traditionally, manual disconnects are provided downstream of the trunk cables and connectors for linking branch cables to the trunk cables. Accordingly, a separate device is necessary solely for the selective, more particularly manual, interruption of power to a component. This again may lead to increased costs both in manufacture and installation.
From time to time, problems may occur in certain devices of the network that require a total or partial shut down of the device or system. Indeed, operations may be brought to a total or partial halt, for example, to diagnose and repair the problem in a specific device. Additionally, total or partial system shutdown may occur in response to an override condition of the system in accordance with an override protocol.
During a shutdown, it may be necessary to disengage operating power to a load, such as a motor, for the purposes of repair. Generally, while a component is undergoing repair, it may be disengaged from main power and, as such, becomes divorced from the system. In conventional networked systems, this may also lead to a loss of operating power, and even data, to the control devices connected to the load, such as relays, protective circuitry, sensing circuitry, actuators, controllers, drives, and so forth. Without these power and data signals, it may be difficult for a technician to conduct diagnostic analysis of the component or system as a whole. This can lead to increased repair and downtimes for both the system and the component. Accordingly, it would be desirable, during diagnostic tests of the system, to disengage the main power while maintaining a second level of power and data signals to and from one or more disengaged components.
As discussed below, the present technique addresses many of these concerns.