en60950-1
Simply said functional insulation is insulation type where some different parts of circuitry are seperated from each other. That is, components are insulated. However, an electrical shock is NOT prevented for e.g. an end-user.
You can find a good definition under
**broken link removed**
Single fault condition means a condition in which one means for protection against hazard is defective. If a single fault condition results unavoidably in another single fault condition, the two failures are considered as one single fault condition.
Hope it helps.