A monitor/analyzer for an ac electrical system can be programmed through a display on the front panel to respond to selected events by generating triggers signals when selected monitored electrical parameters including neutral current exceed programmed thresholds. The trigger signals initiate simultaneous...http://www.google.co.uk/patents/US5706204?utm_source=gb-gplus-sharePatent US5706204 - Apparatus for triggering alarms and waveform capture in an electric power system 
