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"P5A" redirects here. For a planned Mars spacecraft, see AMSAT § Current projects.
PRR P5a mod.jpg
P5a (modified) #4780.
Type and origin
Power type Electric
Builder PRR Altoona Works (13)
Baldwin-Westinghouse (54)
General Electric (25)[1]
Build date 1931–1935
Total produced 92
Configuration 4-C-4
UIC classification 2'Co2'
Leading wheel
36 in (910 mm)[2][3][4]
Driver diameter 72 in (1,800 mm)[2][3][4]
Trailing wheel
36 in (910 mm)[2][3][4]
Wheelbase 49 ft 10 in (15.19 m) (total);
20 ft (6.1 m) (rigid)[2][3][4]
Length 62 ft (19 m)[2][3][4]
Width 10 ft 6 in (3.20 m) (P5, P5a, P5b);[2][3]
10 ft 8.25 in (3.2576 m) (P5a (modified))[4]
Height 15 ft (4.6 m) over locked-down pantographs[2][3][4]
Axle load 74,000 lb (34 t) (P5, P5a);[2]
77,800 lb (35.3 t) (P5b);[3]
77,000 lb (35 t) (P5a (modified))[4]
Weight on drivers 220,000 lb (100 t) (P5, P5a);[2]
444,700 lb (201.7 t) (P5b, all wheels driven);[3]
229,000 lb (104 t) (P5a (modified))[4]
Locomotive weight 392,000 lb (178 t) (P5, P5a);[2]
444,700 lb (201.7 t) (P5b);[3]
394,000 lb (179 t) (P5a (modified))[4]
Electric system(s) 11 kV AC @ 25 Hz
Current collection
Traction motors 6 × 625 hp (466 kW) AC motors;[2][4] plus 4 × 375 hp (280 kW) motors on the trucks on P5b[3]
Transmission AC current fed via transformer tap changers to paired motors geared (25:97) to quill drives on each driving axle;[2][4] plus single motors geared to driving axles on end trucks on P5b (gear ratio: 17:50)[3]
Operator(s) Pennsylvania Railroad
Number(s) 4700–4791
Preserved 4700
Disposition Museum of Transportation in St Louis, Missouri

The Pennsylvania Railroad's class P5 comprised 92 mixed-traffic electric locomotives constructed 1931–1935 by the PRR, Westinghouse and General Electric.[1] Although the original intention was that they work many passenger trains, the success of the GG1 locomotives meant that the P5 class were mostly used on freight. A single survivor, prototype #4700, is at the Museum of Transportation in St Louis, Missouri.

They had a wheel arrangement of 4-6-4 in the Whyte notation, or 2'Co2' in the UIC classification system — three pairs of driven wheels rigidly mounted to the locomotive, with a two-axle unpowered truck at each end.[2][3][4]

The first P5s were built with box cabs. A grade crossing accident in which the crew were killed led to the substitution of a streamlined steeple type cab in later production, a design which was also applied to the GG1.

Table of P5 locomotive production
Year Builder Bodystyle Road numbers Notes
1931 Altoona Boxcab 7898-7899 Class P5, Renumbered 4700 & 4791 respectively in 1933
1932 Westinghouse Boxcab 4701–4732 4702 rebuilt to P5b in 1937
1932 General Electric Boxcab 4755–4774 4770 rebuilt as Modified in 1945
1933 Westinghouse Boxcab 4733-4742
1934 Altoona Modified 4780
1935 Westinghouse Modified 4743–4754
1935 General Electric Modified 4775-4779
1935 Altoona Modified 4781-4790

When the GG1s were put in passenger service, the P5s were regeared and used in freight service for many years. The last of the class was withdrawn from service in April 1965.[5]

P5 prototypes[edit]

Two prototype locomotives were outshopped from the PRR's Altoona Works in 1931.[1] They were essentially the PRR's 2-B-2 O1 design lengthened by adding another pair of driving wheels; while the O1 was an "electric Atlantic" equivalent to the E6s steam locomotive, the P5 was an "electric Pacific" designed to match or better the performance of the PRR's ubiquitous K4s Pacifics.

These prototypes had electrical equipment from both Westinghouse and General Electric; the design was by both companies and the PRR's electrical department, and the equipment from either manufacturer was identical.

P5a production locomotives[edit]

Orders were placed for 90 production locomotives classified P5a due to minor changes from the prototypes (notably, larger traction motor blowers).[1] Production was split between General Electric and Westinghouse; the GE examples were assembled at GE's Erie, Pennsylvania facility, still a locomotive assembly plant today, while final assembly for the Westinghouse order was subcontracted to the Baldwin Locomotive Works.

P5a (modified) steeplecabs[edit]

A fatal grade crossing accident on the New York Division confirmed traincrews' concerns about safety when the crew were killed after colliding with a truckload of apples.[1] A redesign was undertaken, giving the locomotives a central "steeple cab", raised higher, with narrower-topped, streamlined "noses" to the locomotive to enable the crew to see forward. The final 28 locomotives were built to this design, which was not given a separate class designation since it was mechanically and electrically identical; they were called class P5a (modified), and colloquially Modifieds.[1]

Documentation published in 2010 disproved the decades long belief that the modified P5's new shell design came first and was then applied to the to the GG1, R1, and eventually the DD2. Instead, it was revealed that the GG1 project, under the direction of industrial designer Donald R. Dohner, was the first to receive the center cab design, and that soon afterward it was applied to the R1 and P5.[6]

The Modified units (along with the R1 and prototype GG1) were built with riveted carbodies. However, unit #4770, rebuilt to a Modified appearance in January 1945 after being wrecked, differed from previous Modifieds in having an all-welded carbody, the type of construction famously utilized in the production run of the GG1.[7]

P5b experiment[edit]

In October 1937 P5a #4702 was rebuilt with motors in its trucks to become the only locomotive in subclass P5b. Each truck axle was given a 375-horsepower (280 kW) motor, adding 1,500 hp (1,100 kW) to give a total power output of 5,350 hp (3,990 kW). This modification also meant that locomotive's entire weight was carried on driven wheels. Despite these advantages, the experiment was not repeated; #4702 continued in its modified form, however. Staufer & Pennypacker in Pennsy Power state that the experiment was less than successful due to problems in cooling the motors in the trucks.[1]

Visually, class P5b could be distinguished from a boxcab P5a by having a lower row of ventilation grilles on the sides of the superstructure, and by having outside brake cylinders on the trucks.[1]

See also[edit]


  1. ^ a b c d e f g h Staufer, Alvin (1962). Pennsy Power. Staufer. p. 298. LOC 62-20878. 
  2. ^ a b c d e f g h i j k l m Pennsylvania Railroad. "P5 & P5a". PRR Locomotive Diagrams. Retrieved 2008-08-29. 
  3. ^ a b c d e f g h i j k l m Pennsylvania Railroad. "P5b". PRR Locomotive Diagrams. Retrieved 2008-08-29. 
  4. ^ a b c d e f g h i j k l m Pennsylvania Railroad. "P5a (modified)". PRR Locomotive Diagrams. Retrieved 2008-08-29. 
  5. ^ Pennsylvania Railroad Technical and Historical Society (August 2004). "PRR Chronology 1965". Retrieved 2008-08-30. 
  6. ^ Wayt, Hampton C. (Fall 2010). "Update on the GG1's genesis". Classic Trains (Kalmbach) 11 (3): 86–87.
  7. ^ Volkmer, William D. (1991). Pennsy Electric Years. Edison, New Jersey: Morning Sun Books. pp. 26–27. ISBN 1-878887-01-7. 

Original courtesy of Wikipedia: http://en.wikipedia.org/wiki/PRR_P5 — Please support Wikipedia.
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