The power went out for the third time in three weeks in Tranent this afternoon.
ScottishPower said homes and businesses were affected after a fault in a 33,000 volt cable.
Engineers are expected to work through the night to resolve the problem.
The power company said most people affected had power restored within 35 minutes.
A fault at the Tranent substation plunged homes in the town and surrounding area into darkness twice in recent weeks.
A ScottishPower spokesman said: "We were able to restore power remotely and engineers are working through the night.
"We apologise for any inconvenience caused."
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules hereComments are closed on this article