Unknown assailants blew up an electricity pylon feeding west Cairo and a district north of the capital, state-run news agency MENA reported.
The explosion late Wednesday damaged the 500kv tower but didn't cause it to topple, MENA added on Thursday.
Repairs should take two weeks and cost LE400,000 (around $56,000), with necessary diversions carried out to prevent power shortages in affected areas, said Gaber El-Desouky, head of Egypt's main power operator.
Wednesday's incident is not the first of such attacks.
Officials say Egypt's electricity grid has come under frequent attack by unknown assailants targeting electricity substations, towers and circuits in several parts of the country.
Egypt has already been plagued by recurrent summer blackouts due to a severe energy crunch.