In late 1912, PRR engineers recommended large-scale electrification of PRR lines with
alternating current (AC) at 11,000 volts and 25 cycles, starting with the suburban service along the Main Line between
Philadelphia and
Paoli. This project was authorized soon thereafter. In 1914, the PRR started adding AC electrical equipment to 93 MP54-type cars at the
Altoona shops for use in this service. Each car received a
pantograph, a
transformer, a power
truck, a motorman's cab and controls at each end, and MU circuits. These cars were then designated MP54E to distinguish them from non-electrified cars. The Paoli line opened with electrical service in 1915 with great success, and other Philadelphia suburban lines were electrified in succeeding years. By 1933 the entire PRR line from Philadelphia to Penn Station had been provided with AC electrification and the lines from Philadelphia to
Washington, D.C. and
Harrisburg were subsequently electrified as well. MP54 cars then provided local service throughout this area. Large numbers of MP54 MU cars were obtained both by electrifying existing non-electrified MP54 cars and by purchasing and building entirely new cars. As improved electrical equipment was developed in later years, a numeral was added to signify the type of this equipment. Between 1926 and 1930 a further 144 cars were delivered from PRRs main shops in
Altoona, Pennsylvania and Standard Steel in the class MP54E2. Between 1932 and 1937, a total of 46
married pairs were constructed by Altoona that consisted of an unpowered trailer (designated T) that was towed by a motor car (designated E3), with 736 total horsepower compared with the normal 400: 34 (MP54E3+MP54T) + 4 (MP54E3+MBM62T) + 8 (MPB54BE3+MP54T). These special trailer motors could be identified by a small golden keystone above the number on the side of the car. They also had larger
louvers on the side due to the greater demand for cooling air. Small capital letters are awkward to use, so many books have used the LIRR scheme of omitting the initial M for the non-electrified cars (P54) In 1950, faced with the need for expensive new equipment for unprofitable suburban service, the PRR decided to extend the life of the MP54 cars instead of buying new equipment. The MP54s were rebuilt at PRR's Wilmington, DE electric shops with an initial batch of fifty cars in the class MP54E5. A follow-up batch of fifty 508 hp cars in the class MP54E6 were rebuilt at the Altoona shops (for unknown reasons, the designation MP54E4 was skipped). In addition to the new, more powerful propulsion gear, other new equipment was installed including
roller bearing equipped equalized
trucks, new windows, and recessed transit-type lighting In 1951 there were a total of 481 AC MP54 cars of all types in service, consisting of 405 MP54, 42 MP54T, 10 MPB54B, 9 MPB54, 7 MB62, 4 MBM62, and 4 MBM62T cars.
Performance While state of the art in 1908, when the last brand new MP54 rolled off the assembly line 28 years later, the design did more to suit the PRR's desire for standardization than the comfort of the passengers that rode them. Each motor car was powered by a single truck at the pantograph end which in turn was equipped with two 25 Hz
series wound AC motors. Using AC motors of this type resulted in poor acceleration compared to equivalent DC motors, a problem that was exacerbated by the frequent stops the MP54s would make in local commuter service. While the 99 E5 and E6 units rebuilt in the 1950s had better performance and a stated top speed of , older E1 and E2 cars would struggle to reach . A further design flaw in the propulsion gear of the E1 and E2 models required that if power was taken off at speeds above , it could not be reapplied until the train slowed back to 30 mph lest arcing damage the motors. The 1908
truck design provided little in the way of ride quality, and
friction bearings on unmodified cars retarded performance further. Noise from the primitive toothed gear drivetrain (a characteristic common to contemporary MU cars on other railroads) could become quite loud at high speed which made the relative quiet of unpowered trailer cars (if utilized) attractive to some regular riders. == Service history ==