FAST recently re-engineered a multivendor IEC 61850 Station Bus Substation Automation System using a top down engineering approach for system specification and integration. The project was a proof of concept put forward to a utility to replicate an already in service design to highlight engineering design efficiencies. The following is an outline of the process of engineering the system and resulting CID files through HELINKS System Tool Set. The results were then compared to the utility’s commissioned CID files which were created using multiple Vendor Tools.