| PRR FF1 | |
| Powertype: | Electric |
| Builder: | Altoona Works with Westinghouse |
| Builddate: | 1917 |
| Totalproduction: | 1 |
| Aarwheels: | 1-C+C-1 |
| Uicclass: | 1′C+C1' |
| Leadingdiameter: | 360NaN0 |
| Driverdiameter: | 720NaN0 |
| Length: | 76feet |
| Height: | 14feet |
| Locoweight: | 516000lb |
| Weightondrivers: | 439500lb |
| Electricsystem: | 11 kV 25 Hz AC Catenary |
| Collectionmethod: | Pantograph |
| Transmission: | Rotary converter supplied 25 Hz three phase alternating current fed to motors able to run at one of two speeds and connected to the drivers through Jackshafts and side rods |
| Tractionmotors: | 4× Westinghouse model 451 1910hp three-phase motors |
| Maxspeed: | 20.6mph |
| Poweroutput: | 4600lk=onNaNlk=on |
| Tractiveeffort: | Continuous: 87200lk=onNaNlk=on Starting: 140000lk=onNaNlk=on |
| Operatorclass: | FF-1 |
| Numinclass: | 1 |
| Retiredate: | 1940 |
| Disposition: | Scrapped |
The Pennsylvania Railroad's class FF1 was an American electric locomotive, a prototype numbered #3931 and nicknamed "Big Liz". It was built in 1917 to haul freight trains across the Allegheny Mountains where the PRR planned to electrify. "Big Liz" proved workable but too powerful for the freight cars of the time with its 4600 available horsepower and astonishing 140000lk=onNaNlk=on of tractive effort. Pulling the train it regularly snapped couplers and when moved to the rear as a pusher its force was sufficient to pop cars in the middle of the train off the tracks.
It had a 2-6-6-2 wheel arrangement in two half-frames, connected in the center. Each frame had a pair of three-phase AC induction motors driving a jackshaft through gearing and a spring drive; side rods then drove the wheels. The jackshafts can be mistaken for an additional fourth axle but the "wheels" are cogwheels to transfer power from the motors to the jackshaft. Three-phase power for the 4 massive motors was supplied from the single phase overhead supply via a large rotary converter housed in the body of the locomotive. Combined rated output of the motors was 7640hp, but the converter could only supply a short term 4600lk=onNaNlk=on or a continuous 4000hp. With three-phase induction motors there was no way to control the speed of the motors; changing the wiring of the motor poles allowed for two speed settings, 10.3mph20.6mph, which were considered enough to drag heavy freight trains up and down steep grades.
Its intended use as an Allegheny climber never realized and its power too much for the rolling stock in service at the time, Big Liz was sidelined until being cut up for scrap in 1940.