The transformer -- on the corner of Power Road and University Drive in northeast Mesa -- caught fire this morning about 11:45, leaving about 30,000 residents without power.
However, Salt River Officials now say that number has grown to 80,000.
The cause of the fire remains unknown.
"Around these times [of extremely hot weather] there's more demand and stress on our system," Jeff Lane, spokesman for SRP tells New Times. "It could've been high temperatures, equipment failures. We won't know for a couple days. When it's hot, sometimes we have equipment breakdowns."
Mesa firefighters were called to the scene this morning and battled the blaze with foam, Captain Forrest Smith, the fire department's public information officer, tells us.
A huge column of smoke from the fire could be seen across the Valley. More than a dozen fire trucks responded to the scene, where it took firefighters about three hours beat the flames into submission.
"I haven't seen a fire this size in a long time," Smith says. "This kind of thing doesn't happen that often."
While the fire is "completely under control," authorities say, SRP still has to redirect power from other areas of the Valley to Mesa and Apache Junction residents. The process can take a while, Lane says, leaving residents in the dark for the next couple hours.