Faulty power cables led to the disruption of the Circle Line in September that affected some 27,000 commuters, a probe into the incident found.
In a statement on Friday, the Land Transport Authority (LTA) said based on its investigation that the breakdown was caused by a damaged direct current (DC) cable at Dakota station.
Checks also found that the deterioration of the defective cable was made worse by the presence of water in some cable pits.
LTA’s contractor then replaced the damaged cable at Dakota station and conducted checks on all DC cables that were installed for the train line.
Three other cables found to be at risk during the probe have since been replaced.
Subsequent laboratory tests conducted revealed manufacturing defects in some batches of the cables as well as damage in some cables sustained during the installation process, LTA explained.
While these defects do not immediately affect MRT operations, LTA said it will embark on a planned cable replacement programme to replace the defective cables for greater MRT service reliability.
LTA added that checks will be done every three months to make sure the cables have not deteriorated.
SMRT will also work with LTA to conduct frequent insulation tests on the cables and regular inspections of cable pits to ensure that they are dry, the agency said.
The replacement programme is targeted to for completion by end-December 2015. Passenger service will not be affected during the cable replacement programme.
Costs for the programme will be borne by the contractor.
As findings show that SMRT is not at fault for the damaged cable, no penalty will be imposed on the operator for this incident, LTA said.
The four-hour disruption occurred on 20 September, despite the Circle Line being relatively new, and came before two major train breakdowns along the North-South Line last December.
Earlier this year, a two-and-a-half-hour disruption on the Circle Line affected 18,000 people during peak morning traffic on 18 April.
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