The M8 is similar in design to the M7 car used on the Harlem Line and the Hudson Line. Like the M7, the M8 is able to pick up 750 Volt DC direct current power from underrunning third rail for operation along the New Haven Line from Grand Central Terminal to Pelham, where the traction power source is transferred to the overhead catenary wire. The overhead wire is at a nominal 12.5 kV AC power from overhead lines via pantographs for operation from Pelham, New York to New Haven, Connecticut (as well as along the New Canaan Branch), and 25 kV AC power from catenary for operation along the Shore Line East route east of New Haven to New London, Conn. Unlike in earlier classes, changeover between the two AC voltages can be made by the engineer while on the move.