Catastrophic fire conditions on December 21 saw 130 power poles damaged overnight in the Green Wattle Creek fire affecting Wingecarribee and Wollondilly shire.
An Endeavour Energy spokesperson said it will take time to repair power to houses.
"We are still scoping the damage and repairing what we can," they said.
"The damage is significant.
"We are limited to where we can go due to the active fires.
"We cannot give a precise estimation at this time.
"Residents should be prepared to be without power and seek alternative accommodation if possible."
Anyone who sees a fallen power line is advised to stay away by eight metres and assume that the power pole is live.
The number to report fallen power poles is 131003
Please see www.endeavourenergy.com.au/outages for the latest updates on estimated restoration times.