Some work activities in electrical installations are sensitive to unexpected sources, especially when working on conductors to be broken or joined or on overhead lines. Generally there is uncertainty about existence, gravity level, risk or seriousness of exposure to the unexpected sources. The possibility of unexpected electrical energy, the need for additional protective measures and its resolution frequently are decisions made under pressure in the field, entrusted to the person performing the work. The authors submit that methods to detect unexpected energy sources, together with guidelines for addressing such situations, can and should be developed for incorporation into safety procedures. The authors also indicate approaches to system design that can reduce exposure to unexpected power sources.