SINGAPORE - Monday's train breakdown was due to a power fault within the western sector of the North-South and East-West Lines (NSEWL), said the Land Transport Authority (LTA) on Tuesday (April 26).

In reply to queries from The Straits Times, the LTA said: "Checks carried out during engineering hours indicated that the circuit breaker trip was not due to a power dip, but a power fault within the western sector of the NSEWL."

A circuit breaker is a device that "breaks" an electrical connection when there is high resistance, a surge or a stray current. When it trips, it cuts off the flow of electricity.

The LTA added that more checks will be carried out after train operations end on Tuesday (April 26) and that it is working with SMRT to find the root cause of the breakdown.

Train services along the NSEWL, Circle Line (CCL) and Bukit Panjang LRT Line were disrupted last night, delaying the journeys of thousands of commuters near the end of the evening peak.

The power trip, which occurred at 7.53pm, led to blackouts and a loss of air-conditioning at all affected stations. They were without power except for emergency lighting.

Train services were unavailable for between 30 minutes and two hours.

The LTA said it is working with SMRT to investigate the cause of the power faults and that preliminary investigations have found that the 22kV circuit breakers at Buona Vista station had tripped.

The Buona Vista power intake station supplies power to the western sector of the NSEWL and parts of the CCL, said LTA, and hence affected train services on the NSEWL from Buona Vista to Joo Koon and Jurong East to Kranji, and the CCL from Harbourfront to Caldecott.

"As the Bukit Panjang LRT system receives power from the same source through Choa Chu Kang on the NSEWL, it was similarly affected," it added.