As the IEC 61850 system expands, there will be occasions where you need to interface physical I/O to the LAN and represent them as a specific Logical Node preferably with the correct Logical Node and its associated semantics in order to maximise the benefits in the engineering process. Certainly there are a range of IEDs such as relays, meters, bay controllers etc that provide digital inputs and outputs. In many cases however, these IED tools force the Systems Integrator to allocate these as GGIO and all the benefit of semantics is lost. As an example without specifically promoting any one system as vendors like ABB, SEL ... all have similar Remote I/O units, this very effective unit known as the Cube Controller from SystemCORP provides the ability to nominate the Logical Node type associated with the physical input or output, thereby maintaining maximum benefits in the engineering process. https://www.systemcorp.com.au/products/hardware/cube-controller/ It can be located within the control room or as part of the physical plant - eg the circuit breaker in order to bring back the CB position status or receive the trip/open/close messages to minimise wiring (note a single 52a and 52b contact together with a single trip/close connection requires a minimum of SIX WIRES - there are usually multiple 52a and 52b contacts and often duplicate trip wiring separated from the open/close control wiring which can be replaced by the SAS LAN ) It is also a useful solution to interfacing legacy electromechanical devices into the SAS LAN as shown below:   
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