Wrong Code Downloaded to PLC Causes Plant to Shutdown

When making minor changes to a PLC program, the PLC and Slave PLC were loaded with the new program and made the Master. The new Slave, previously the Master, was also loaded halfway through this download. The Master PLC stopped working and the plant was shut down. On a previous training course, the instructions were always to download to both units. However, a colleague, unaware of what had been taught on the training course, had discovered that it was possible to run different programs on the Master and Slave on a previous occasion, as long as they were not too dissimilar.

The plant was shutdown for 1