INFREQUENT REPORTS of severe mechanical damage to small transformers as a result of nearby lightning strokes have led to the conclusion that the cause of the damage was the passage of heavy lightning currents in opposing directions in the two halves of the low-voltage windings. These cases have been rare but are of considerable interest as they have led to the consideration of the effects of the more frequent lightning currents of smaller magnitude flowing in distribution-transformer low-voltage windings.