Results of the investigations into the 7 July NSEWL incident

The Land Transport Authority (LTA) and SMRT held a press conference this afternoon (29 Jul’15) to update the media that the joint investigation, which was carried out with the assistance from consultants from Sweden and Japan, have determined the cause of the North-South East-West Line (NSEWL) train disruption on 7 July 2015.


What was the root cause?

It was found that water was dripping onto the third rail near an insulator in a stretch of tunnel between Tanjong Pagar and Raffles Place. The water (which had natural mineral content) reduced the effectiveness of the insulator. This led to electricity flowing from the third rail into the ground.

This activated the 64P safety mechanism which tripped the power system, causing our trains to stall. The 64P, or “Touch Voltage Protection Relay” is a safety feature on the NSEWL and is used in rail systems all over the world.


What we are doing to prevent a similar incident.

To prevent similar incidents from happening again, SMRT has checked the entire NSEWL tunnels to ensure that there are no other leaks with dripping water.

All third rail insulators are being replaced, starting with those that have shown signs of ineffectiveness. Data loggers are also being installed at all substations to better monitor the condition of the insulators.

The 64P settings will be raised from 136 Volts to 200V, which will make the network less sensitive to power trips. The higher voltage setting, however, is in line with international standards, so the safety of our passengers will not be compromised by this adjustment.

The full media release can be found on the SMRT website here.

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