Our facility has a power management system based on a Siemens S7 PLC monitoring about 100 Siemens 9610 multifunction relays which are daisy-chained together with 4-wire RS485 serial cable. We recently experienced a total loss of facility power, and the power monitoring system completely froze up for at least two minutes right when we needed it most. My present assumption is that the most likely answer is that simultaneous alarming of over 100 remote terminal units attempting to alert the central PLC over daisy-chained serial cable caused a communications bottleneck which lead to a system hangup. Does this seem reasonable or am I chasing a red herring? Is RS485 communications protocol for a real-time power monitoring application such as this that can experience multiple simultaneous alarms? Any thoughts would be greatly appreciated.