BOSTON — A bad electrical connection is to blame for the Red Line derailment that wrought havoc on the MBTA this summer, according to the Fiscal and Management Control Board.
In a report released at the board's meeting Monday, the organization cited "poor electrical connectivity" for causing an axle to fail and fracture, in turn derailing the train and smashing a signal bungalow that is still causing delays.
MBTA trains sit on top of axles that have an onboard motor powered by what is known as the third rail. That 'third rail' along the subway tracks supplies electricity to the axle's motor via a sliding brush. Once the motor has been powered, that electricity is sent to ground through a brush and plate on the axle.
According to the MBTA, the failed axle had issues with the connection between the ground brush and the ground ring. A bad connection, the MBTA says, caused electricity to arc into the axle itself, weakening its structure and ultimately causing its failure.
The control board said the maintenance team has started inspecting the entire MBTA fleet for "fractures or other potential issues" on all lines. The process is expected to be complete in two to three weeks.
Red Line cars are inspected every 8,500 miles, or about every three months, according to the control board. The board said it is adding aditional maintenance and inspection measures to the normal protocol.
An outside lab was hired to conduct an analysis to determine if either contributed to the derailment.
The impacts from the derailment are still affecting the Red Line, over three months later, as trains have had to slow down as the control system for switches is rebuilt. The T has warned riders that regular service may not resume until October.
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