Scottish and Southern Energy's power distribution arm has been penalised for failing to meet a three month-deadline for connecting customers.
The energy regulator Ofgem fined Scottish Hydro Electric Power Distribution (SHEPD) £500,000.
Ofgem said it was "vital" that customers got prompt connections.
The regulator said Perth-based Scottish Hydro co-operated with the investigation and the penalty could have been much higher if it had not.
Stuart Cook, from Ofgem, said: "Customers such as developers of housing estates or wind farms are reliant on local power network companies to provide a good service on connections.