A cut in the insulation layer of a power cable along a rail extension and a rusted component in a circuit breaker led to the massive three-line rail breakdown last year which affected about 123,000 commuters.
This was the conclusion of a months-long forensic investigation into equipment faults on the Tuas West Extension (TWE) that led to disruptions on the North-South, East-West and Circle Lines, Transport Minister Ong Ye Kung said yesterday, as he warned against cutting corners when it comes to rail line maintenance.
Mr Ong was speaking at the ground-breaking ceremony of the new Integrated Train Testing Centre, which will be able to test new trains and rail systems round the clock without disrupting service.
Investigations by main contractor Alstom and the Land Transport Authority (LTA) found a cut in the insulation layer of a cable - likely due to a manufacturing defect or mishandling during installation - had led to a short circuit.
The trip coils in a circuit breaker that should have contained the initial fault failed because a plunger, which moves to enable the circuit breaker to kick in, had rusted.
The rust had likely formed due to inadequate protective coating on the batch of trip coils used on the TWE, and obstructed the plunger.
This led to a disruption of more than three hours and left 6,700 commuters stranded on trains.
"What I described is a very typical story of any major train disruption," Mr Ong said. "When you dig deep enough, you will trace the cause to a few tiny glitches happening at the same time... But this is enough to paralyse a large segment of our train lines."
He said a lot of work and money has gone into rectifying the defects identified in the Oct 14 disruption. Alstom replaced all 113 trip coils, made of carbon steel with nickel coating, along the TWE last year and is replacing all 150km of power cables with higher-specification ones. It is bearing the costs of these works, which have led to early closures and late openings on the East-West Line, and full Sunday closures at some stations till May.
Mr Ong said the trip coils will be replaced with stainless steel ones by the third quarter of next year.
LTA has also adjusted the settings on the space heaters to reduce the humidity level within circuit breakers to lower the chances of rust forming, while SMRT has stepped up the frequency of maintenance to once every three months. It had increased the frequency to once every six months in the wake of the disruption, from once a year before then.
Mr Ong said hard work and spending more on maintenance have resulted in the MRT network clocking over one million mean kilometres between failures today.
But he said that the occasional disruption is inevitable, adding: "When that happens, we will need to get to the bottom of the matter, identify the causes, rectify and learn from the experience.
"Cutting corners on maintenance to save cost is not being productive. It is not contributing towards financial sustainability. It is, in fact, very unproductive, as the remedial action is always disruptive and expensive, and will cost us many times over in social, economic and financial costs."
While maintenance expenditure per place km has doubled over the last decade, Mr Ong said there is no need to "gold plate" maintenance.
"Instead, we need to understand how small, simultaneous glitches tend to be the causes of big disruptions. Let's spend where we need to spend, and where it matters, to ensure safety and reliability.
"Train our workers well, equip them with the skills to spot and rectify problems, to feel safe to whistle-blow where necessary, to proactively improve how maintenance work is done."