Two air conditioners plugged into the wrong socket in the Honolulu police department's radio room caused a power failure that downed O'ahu's 911 system for 13 minutes Wednesday, according to a statement released by Hawaiian Telcom yesterday.

A city contractor connected the air-conditioning units to the wrong circuit, one that serves Hawaiian Telcom's E911 system. The air conditioners were not supposed to be turned on until city engineers inspected and approved the connection, the company said.

That inspection was scheduled for Wednesday morning but someone turned the air conditioners on before the inspectors arrived. The result was a failure of the E911 system's Uninterruptible Power Supply, according to the statement.

Hawaiian Telcom plans to more clearly label its equipment with explicit warnings that any maintenance must have prior approval from the company. The warning will include contact numbers at Hawaiian Telcom, the statement said.