The break of an external electrical power supply cable (63 kV) caused the gradual shutdown of units at a refinery along with a major release of smoke around a distillation furnace. The internal emergency plan was activated (i.e. presumption of fire), the crisis cell alerted and the site partially evacuated. The origin of this smoke was apparently from poor combustion due to a lack of atomizing steam. The services of external fire-fighters were not required.