Following the second black-out in a week affecting Nelly and Picnic Bays, which had no obvious cause, Ergon Energy is dispatching an investigation crew to Magnetic Island tomorrow.

An Ergon Energy spokesman said a Townsville based crew will assist Magnetic Island field staff to undertake a thorough investigation of the main high voltage powerline and equipment that supplies power to both communities.

"The investigation has already started and a Townsville crew is expected to arrive on the island tomorrow. The main powerline runs from Nelly Bay over several hills into Picnic Bay. Some of the powerline runs through hard to access terrain. Our crews will be looking at all aspects of the powerline including associated hardware such as insulators, towers, power poles and cross arms," he said.

Power was lost to about 750 customers during last Wednesday night's rain and strong winds. Crews found no obvious cause of the interruption. A second interruption yesterday cut power to 760 customers in both communities for about two hours.

"This second interruption on the same line with within five days indicates a transient fault which must be addressed quickly," he said

Ergon Energy has apologised for the interruptions and say they will work quickly to find the fault and undertake repairs as required.