A fast, rugged, electronic circuit is described which predicts an impending switching surge flashover in a long air gap and diverts the discharge energy into a triggere'd bypass gap. Prediction is based on the amount of charge injected into the gap by the high voltage electrode. A protective gap could be designed which would operate only if the insulation being protected were about to fail. This could significantly improve the techniques of insulation coordination and has important implications for studies of the mechanisms of the long spark.