A section of cable on the Seaford rail line in Adelaide's south will be replaced after parts of the electric wire snapped in two separate incidents, cutting power to the train.

Transport Minister Stephen Mullighan told 891 ABC Adelaide the first incident occurred in June 2014 and was thought to be an installation problem and an isolated incident.

But after a second incident in a similar area two weeks ago, the section of cable has now been deemed faulty.

"Back in June of last year we inspected the area and then did a full line inspection of the entire system to see if it was something that was throughout the system or if this was an isolated incident," Mr Mullighan said.

"It was thought that it might have been an installation problem, rather than a manufacturing-of-the-cable problem and it was thought that it was an isolated incident, particularly given that we'd inspected the full line.

"What's happened a couple of weeks ago is that we've had a repeat of this issue in a similar area, not the same area, but in a similar part of the line.

"Our advice is, that we've got one section of the cable which was supplied by the cable manufacturer, which is deemed to be faulty and has caused these two outages."

Mr Mullighan said the original major works contractor and cable supplier will replace the faulty section of cable at no cost to taxpayers.

"We have spent hundreds of millions of dollars on this and when this piece of infrastructure, or any piece of infrastructure fails to perform, we expect the contractor to rectify it as soon as practicable and do it at no cost to taxpayers or inconvenience to commuters," Mr Mullighan said.

"It's a significant section, it would be in the kilometres rather than the metres and it's a section of wire between the Seaford section and Hallett Cove."