The lead unit of the class was equipped for AC operation with an overhead pantograph (later two),[1] while the other 24 were third rail DC units to work on the existing PRR third rail electrification in the New York area.

The class was built with an eye towards future long distance electrification[2] with the idea of a single class that could be used interchangeably between the present and future AC electrified zones and the DC electrified zone in New York City.

The original classes were to be simply L5 for the AC units and L5a for the DC units, but as the additional equipment suppliers were brought on the scheme changed to include the intended function (passenger), the current used and finally the electrical supplier.

The L5 was not as successful as the DD1 as the side rod electric locomotive concept proved to be unsuited to the demands of long distance electrification.

Even in the existing short haul service the L5's long rigid wheelbase and poor weight distribution caused it to be withdrawn significantly before the older DD1s.