The L5 was an electric locomotive designed for long-distance passenger service. It had a large central cab and two long, low and narrow hoods which housed the traction motors an other equipment. All four driving axles were mounted in the frame and there was one leading axle on each end. In each hood, two traction motors powered a common jackshaft that was connected to the two adjacent driving axles. In total, the four motors had an output of 3,340 hp. The drivers had a diameter of 80 inches or 2,032 mm in order to reduce the rotational speed of the rods. They were the last electric locomotives built for the PRR with side rod drive.

The first locomotive, later designated class L5pdw, was equipped for service under 11 kV AC via a pantograph on the roof and 650 V DC via third rail. As it turned out that the side rod drive was not optimal for long-distance service, further locomotives were built for the DC-only sections around New York City without a pantograph on the roof. The next twelve were designated L5pdw and also had their electrical equipment from Westinghouse like the first one. Six more each were built with equipment from GE, called L5pdg, and with equipment from BBC, called L5pdb.