Deploying line current differential protection over Ethernet packet switched transport is more than just making the connections, as the application demands certain deterministic characteristics from the communication channel. Packet switched traffic by its very nature of statistical multiplexing is subject to variances in propagation time due to queuing delays, which can impact the performance of line current differential schemes that are dependent on channelbased synchronization. This paper details the results of testing a line current differential system on a Multiprotocol Label Switching (MPLS) based Ethernet packet switched network. A variety of simulations were performed in order to determine if reliable protection could be achieved in such a network. Protection times were measured and reliability assessed. Impacts of a number of potential threats were established and overall protection performance was evaluated. Details on engineering the network to meet the Reliability, Selectivity, Coordination, Sensitivity, and Speed requirements of a line current differential system are provided.