Faulty third rail insulation likely the culprit behind MRT breakdown: SMRT

It affected the supply of traction power.

SMRT said that it has narrowed down the likely cause of the unprecedented 7 July MRT service disruption to the insulation of the third rail.

This insulation is part of the trackside infrastructure that is used to protect power cables that supply electricity to the third rail. SMRT said that it could have affected the supply of traction power and led to the tripping of the Touch Voltage Protection Relay, known by its code 64P, along multiple stretches of the North-South East-West Line (NSEWL).

The 64P relays, which are part of the original design of the NSEWL power network, are designed as a safety measure to mitigate the possibility of unacceptable touch voltage to protect the safety of commuters.

“During last Tuesday’s disruption, SMRT made the decision to halt train services temporarily to investigate the cause of the relays being tripped that resulted in loss of power that affected the train motors, air-conditioning and cabin lighting. This decision was made in order to avoid a situation where a power trip would leave trains stalled in tunnels or on viaducts, which would then force massive numbers of commuters to detrain on track to reach the next station platform,” SMRT said.