An explosion at an electricity substation in the Blue Mountains has left more than 5500 residents in 40-degree heat without power for the second time this week.
NSW Fire and Rescue was called out to the Blaxland substation on Friday night, three days after a fire at the same substation left 7514 people without power.
Residents took to social media to complain, seeking an explanation from Endeavour Energy.
After the first power outage on Tuesday night, the energy company asked residents to "lend them a hand" by limiting their use of airconditioners on Wednesday, on a day when temperatures soared to 39.5 degrees in Blaxland.
"Endeavour Energy is asking electricity customers in the lower Blue Mountains to help limit electricity usage today by turning off pool pumps and limiting the use of airconditioners, where possible, as crews work to repair damaged cables following a fire in its Blaxland Zone Substation last night," the company said on Wednesday.
An Endeavour Energy spokeswoman apologised on Friday night and said a faulty cable was to blame for the second outage.
"Our crews are on site ascertaining what's happening and we are hoping to restore power to the majority of customers in the next few hours.
"Endeavour Energy apologises sincerely to the customers affected and is investigating the cause of both incidents at the substation this week."
NSW Fire and Rescue said they attended on Friday "a small explosion at the substation that had emitted smoke, but no fire".
Power had been restored to 1300 residents by 8.30pm.