Vector says the weather may have played a part in damaging an Auckland substation on Thursday evening.
About 46,00 customers were affected after a power transformer exploded at the Hepburn Road substation at about 6.30pm.
Vector says several lightning strikes were reported throughout Auckland on Thursday.
Crews from both Vector and Transpower, which also has equipment at the Hepburn Road site, are back there on Friday, continuing repairs.
