PRR B1 Electric Switchers: History, Specs & Roster

Last revised: September 2, 2026

The Pennsylvania Railroad class B1 was a small boxcab built to do one job: shuffle passenger cars under wire. Juniata turned out the type between 1926 and 1935—three axle-hung motors, 62-inch drivers, a single pantograph, cabs at both ends, and a 31-foot-6-inch frame that would fit a coach-yard lead. On the PRR diagram they are 0-6-0s. In AAR they are C. In the yards at Sunnyside, 30th Street, and Harrisburg they were the electric equivalent of a steam shifter, and crews called them rats.

Twenty-eight were Pennsylvania engines. Fourteen more, the same Altoona design, went to the Long Island Rail Road as class B3 for Bay Ridge freight. Some class summaries online, and elsewhere, fold all 42 into B1. The railroad did not. Long Island kept its own numbers and class. One B1 survives: 5690, indoors at the Railroad Museum of Pennsylvania in Strasburg.

Pennsylvania Railroad class B1 electric switcher boxcab

Pennsylvania Railroad class B1 electric switchers #3917 and #3907 are seen here at the 44th Street Shops in Philadelphia. American-Rails.com collection.

On this page: At a glance · Why a three-axle boxcab · BB1 and BB2 pairs · The 1934 singles · Long Island B3s · Sunnyside, 30th Street, Harrisburg · Complete roster · Specifications · Retirement and 5690

At a glance

Item	Detail
Railroad	Pennsylvania Railroad (28). Same carbody on Long Island as class B3 (14)
PRR class	B1 (after 1933). Built as BB1 (2), BB2 (12), and B1 (14)
PRR road numbers	3900–3901; 3910–3921; 5684–5697. Five later took 4751, 4752, 4755–4757 in 1966–67
Builder	PRR Juniata Shops (Altoona Works), with Westinghouse (1926 groups) and Allis-Chalmers (1934–35) electrical equipment
Built	1926 (pairs); 1934–35 (singles)
Wheel arrangement	Whyte 0-6-0; AAR C; UIC Co. Three driving axles, no guiding trucks. PRR class B is the 0-6-0, steam or electric
Power	11,000 V, 25 Hz AC overhead (as standardized). BB2 built for 650 V DC third rail; converted to AC 1933–35
Horsepower	Three axle-hung motors at 233 hp each, 700 hp combined. Classic Trains lists 570 hp for the class—the usual continuous figure against the hourly rating
Work	Passenger-terminal switching: Sunnyside Yard and New York Penn Station, 30th Street coach yard in Philadelphia, Harrisburg. Not road freight
Crew name	Rats
Survivor	5690 (briefly Penn Central 4756), Railroad Museum of Pennsylvania, Strasburg. Remainder scrapped

Roster and construction numbers from Eugene Connelly and William Edson, PRR Numerical Roster, Steam and Electric Locomotives (rev. Dec. 29, 2011). Specs from PRR diagram E-400387-B and Alvin F. Staufer and Bert Pennypacker, Pennsy Power (1962), pp. 260–263. Information compiled September 2, 2026.

Why a three-axle boxcab

Pennsylvania Station opened in 1910 with 650-volt DC third rail through the Hudson and East River tunnels. Pennsylvania DD1 motors hauled varnish between Manhattan Transfer and Sunnyside. Steam still made up the trains in the yards. Michael Bezilla’s Electric Traction on the Pennsylvania Railroad is the book on that plant: first the tunnel problem steam could not solve, then the 1928–38 main-line program that put 11,000-volt, 25-cycle catenary from New York to Washington and west to Harrisburg. Once those coach yards sat under wire, a steam 0-6-0 was the wrong tool. The railroad needed a shifter that took power from the same plant as a GG1.

Until 1933 a through train still changed engines at Manhattan Transfer. DD1s owned the tunnels; steam or the new AC road motors owned everything west of the Hackensack. When catenary was carried through to Penn Station, GG1s and P5s ran into Manhattan without a change, and the yards at Sunnyside had to switch those same cars on AC. The B1s were already there as DC pairs. Converting the BB2s and splitting the drawbars was how the terminal kept up with the road.

PRR classification made the carbody obvious. Class B was already the 0-6-0: three driving axles, short wheelbase, no lead truck to bind on yard curves. The electric B1 is that idea in a boxcab. Three universal motors geared straight to the axles. One pantograph on the roof centerline. Controls at both ends so the engine did not have to run around a cut. Top speed 25 mph—enough to drag a cut of head-end cars and coaches through Sunnyside, not enough to get in a GG1’s way on the main. Starting tractive effort was 39,250 pounds on 157,000 pounds of engine. That is a high factor of adhesion for a yard goat, which is what you want when the cut is P70s on wet rail and there is no room to slip.

They are not the steam B1, an 1860s 0-6-0T. Same letter, different century.

Married pairs: BB1 and BB2

The first twenty-eight locomotives left Juniata in 1926 as semi-permanently coupled pairs. Two B units together were class BB, the same doubling PRR used on DD1s. More motors, more tractive effort, still a yard engine.

The prototype pair, class BB1, was 3900 and 3901, construction number 4080, built as New York Terminal No. 8. They were AC from the start. They proved the carbody. Production for the New York terminal was class BB2: twelve locomotives, six pairs, 3910–3921, construction numbers 4031–4036, New York Terminal 1 through 6. Those twelve were 650-volt DC third-rail engines, with contact shoes, to live in the same plant as the DD1s between Penn Station and Sunnyside.

When the AC catenary from the south reached the New York terminal in 1933, the pairs came apart. The BB1s and BB2s were reclassed B1 as single units. The twelve DC engines were rewound and given pantographs for 11,000-volt, 25-cycle AC. After that the whole PRR fleet spoke the same language as the road motors.

Fourteen singles for the expanding wire

The last order did not bother with drawbars between units. Fourteen locomotives, 5684–5697, came out of Juniata in 1934 and 1935 as single-unit class B1 from the start, Allis-Chalmers electrical equipment, AC overhead. Construction numbers run 4257 through 4273 with the usual Juniata gaps. Harrisburg passenger electrification was finishing in those same years; Philadelphia’s 30th Street coach yard was already under wire. The railroad needed extra singles, not more married pairs for the old DC terminal.

These are the engines Bert Pennypacker photographed at Harrisburg—5687 in the 1940s, at the west end of passenger electrification. Robert S. McGonigal, summarizing the class for Classic Trains, called the B1 a member of North America’s largest fleet of electric switch engines. Count only the PRR roster and the class is 28. Count the Long Island sisters and the type is 42. Either way, no other American railroad put that many purpose-built electric switchers under one roof.

Long Island’s B3s

The same shops built fourteen more in 1926 for the Long Island Rail Road, which the Pennsylvania still controlled. They went to the Bay Ridge Branch as class BB3, seven pairs numbered 324–330 with A and B halves, 11,000-volt AC to match New Haven catenary on the freight line from Fremont to the Bay Ridge float yards. They were more locomotive than the branch needed as pairs. Long Island split them into fourteen singles, class B3, numbered 324–337. Edward M. Koehler’s LIRR motive-power summary has them stored after Bay Ridge freight electrification was cut back in the mid-1950s and gone by 1955. Three—324, 325, and 332—were sold as-is to the Pennsylvania on February 24, 1954. They are the same machine as a B1. They are not the PRR B1 roster below.

Sunnyside, 30th Street, Harrisburg

The work was passenger-terminal switching, not the freight main. Sunnyside Yard in Queens was the big assignment: make up and break up the Fleet of Modernism, drag deadhead consists through the East River tunnels, spot head-end cars at Penn Station. Philadelphia’s 30th Street coach yard took a share. A few ran at Harrisburg once the 1938 wire reached the west end of the passenger electrification. They did not go to Enola to switch freight. That remained steam, then diesel.

Yard crews called them rats. The name stuck on Long Island as well as at Sunnyside. A three-axle boxcab darting in and out of coach tracks will do that. It was never a company class name. It is what the men who ran them said.

As through passenger business thinned in the 1950s and 1960s, the railroad needed fewer dedicated electric switchers. Diesel SW1s and their kin could work a dark yard. The B1s could not. Harrisburg and Philadelphia let theirs go first. Sunnyside kept rats the longest. A handful were still on the property when Pennsylvania and New York Central became Penn Central on February 1, 1968. None lasted into Conrail in 1976 as working engines.

Complete PRR B1 roster

Construction numbers are Juniata shop numbers. Pair mates share a number. Dispositions are Connelly and Edson. Five units took 4750-series numbers in 1966–67 to clear the old series; 5690 was one of them and is the engine at Strasburg, restored to 5690.

PRR no.	As built	Built	C/N	Original pair / NY Terminal	Disposition
3900	BB1	1926	4080	With 3901; NYT 8	Scrap Dec. 1962
3901	BB1	1926	4080	With 3900; NYT 8	Scrap Dec. 1962
3910	BB2	1926	4031	With 3911; NYT 1. DC, then AC	Sold for scrap Aug. 1967
3911	BB2	1926	4031	With 3910; NYT 1	Scrap Jan. 1962
3912	BB2	1926	4032	With 3913; NYT 2	Renumbered 4751 Oct. 1966; retired, held for display; not the Strasburg engine
3913	BB2	1926	4032	With 3912; NYT 2	Renumbered 4752 Mar. 1967; retired
3914	BB2	1926	4033	With 3915; NYT 3	Scrap Dec. 1962
3915	BB2	1926	4033	With 3914; NYT 3	Scrap Jan. 1963
3916	BB2	1926	4034	With 3917; NYT 4	Scrap Dec. 1962
3917	BB2	1926	4034	With 3916; NYT 4	Scrap Dec. 1962
3918	BB2	1926	4035	With 3919; NYT 5	Scrap Dec. 1962
3919	BB2	1926	4035	With 3918; NYT 5	Sold for scrap Aug. 1967
3920	BB2	1926	4036	With 3921; NYT 6	Scrap Aug. 1958
3921	BB2	1926	4036	With 3920; NYT 6	Scrap Jan. 1962
5684	B1	1934	4257	Single, AC	Scrap Jan. 1967
5685	B1	1934	4258	Single, AC	Scrap Feb. 1967
5686	B1	1934	4259	Single, AC	Scrap June 1960
5687	B1	1934	4260	Single, AC	Renumbered 4755 Nov. 1966
5688	B1	1934	4261	Single, AC	Scrap May 1967
5689	B1	1934	4262	Single, AC	Scrap Jan. 1963
5690	B1	1934	4263	Single, AC	Renumbered 4756 Feb. 1967. Preserved, Railroad Museum of Pennsylvania, restored as 5690
5691	B1	1934	4264	Single, AC	Scrap Feb. 1962
5692	B1	1934	4265	Single, AC	Scrap May 1967
5693	B1	1934	4266	Single, AC	Renumbered 4757 Feb. 1967
5694	B1	1935	4268	Single, AC	Scrap Feb. 1967
5695	B1	1935	4270	Single, AC	Sold for scrap Aug. 1967
5696	B1	1935	4271	Single, AC	Retired Dec. 1963
5697	B1	1935	4273	Single, AC	Scrap Sept. 1962

All 28 reclassed B1 when the pairs were split in 1933. BB2 units converted from 650 V DC third rail to 11 kV 25 Hz AC at the same time. Long Island 324–337 (class B3) are omitted here; they are the same design, not PRR numbers.

Specifications

Figures below are the PRR AC diagram (tracing E-400387-B) as published by Staufer and Pennypacker and by the railroad’s own drawing. BB2 dimensions as DC engines were the same carbody with third-rail shoes instead of a pan.

Item	Detail
Builder	PRR Juniata Shops, Altoona Works
Electrical equipment	Westinghouse (1926 BB1/BB2); Allis-Chalmers (1934–35 B1)
Type	Rigid-frame boxcab switcher, dual-end controls
Wheel arrangement	0-6-0 / AAR C / UIC Co
Driver diameter	62 in
Length	31 ft 6 in
Height	15 ft 0 in (pantograph down)
Weight	157,000 lb
Track gauge	4 ft 8½ in
Current collection	One overhead pantograph (AC). BB2 as built: third-rail contact shoes, 650 V DC
Line voltage (standard)	11,000 V, 25 Hz AC
Traction motors	Three AC/DC universal motors, axle-hung, geared to the axles
Motor rating	233 hp each
Power output	700 hp combined (hourly). Classic Trains: 570 hp (continuous class figure)
Starting tractive effort	39,250 lbf
Maximum speed	25 mph
Control	Tap-changer AC (or resistance control on the original DC BB2s)

What survived

Connelly and Edson put the first retirement in August 1958 (3920) and the last scrap sales in August 1967. 3912 was held for display after it became 4751. The engine the Commonwealth of Pennsylvania actually kept is 5690, built in 1934, construction number 4263, briefly Penn Central 4756, restored to 5690 and standing on Track 5 in the museum hall at Strasburg beside the DD1 pair, GG1s 4800 and 4935, and E44 4465. It is cosmetic. There is no 11,000-volt switcher lead left to run it on.

Sources

Alvin F. Staufer and Bert Pennypacker, Pennsy Power: Steam and Electric Locomotives of the Pennsylvania Railroad, 1900–1957 (Carrollton, Ohio: Alvin F. Staufer, 1962), pp. 260–263
Pennsylvania Railroad locomotive diagram E-400387-B (class B1, AC), via Robert Schoenberg, prr.railfan.net
Eugene Connelly and William D. Edson, PRR Numerical Roster, Steam and Electric Locomotives, rev. Dec. 29, 2011
Robert S. McGonigal, “Pennsylvania Railroad electric locomotives,” Classic Trains (online class summary)
Edward M. Koehler Jr., LIRR motive-power history, 1898–1955
Michael Bezilla, Electric Traction on the Pennsylvania Railroad, 1895–1968 (University Park: Pennsylvania State University Press, 1980)
Railroad Museum of Pennsylvania roster (5690)
Trainweb / BEDT industrial locomotive notes on LIRR BB3/B3