INDIANAPOLIS (AP) _ Indianapolis Power and Light says it has asked another company to investigate what caused an underground explosion in downtown Indianapolis

IPL spokesman Brad Riley tells WISH-TV and The Indianapolis Star that it has asked power management company Eaton to investigate. He says Eaton made the network protector _ a sort of circuit breaker _ that IPL blames for the explosion near the Circle Centre shopping mall.

Riley says the investigation could take three months.

He says the underground transformer vault where the explosion occurred was last inspected in 2012.

No one was injured in the explosion, which sent smoke billowing into the street and prompted the evacuation of nearby offices.

A 2011 report commissioned by state regulators found IPL needed to improve in finding and fixing downtown electrical failures.