The Johnson City Power Board confirmed power outages occurred in areas from Gray to Greene County Sunday at around 5 p.m.
The Power Board was able to restore power to all affected areas in just under an hour.
According to J.T. McSpadden, a spokesman for the Power Board, more than 20,000 customers were affected by the outage when a primary substation went out, subsequently taking out seven distribution stations with it.
McSpadden said a faulty transmission line caused the mass outage, but what caused the line to go faulty is unknown.
“In this case, we don’t know what happened yet,” McSpadden said. “It could be an animal. It could be a tree. It could be a lot of things.”
He said there are a lot of variables, and they might ultimately might not find out what caused the outage.