Contactor Operation

Annual inspection work on the 309 provided a good opportunity to document and explain the operation of the contactors on this car. First, some history: the first successful multiple-unit operation was in Chicago, in 1898, using a system designed by Frank Sprague for the South Side Rapid Transit. Three years later, General Electric developed the first widely-used form of electomagnetic contactor control, known as Type M. Type M was a system which used a master controller to energize different high-voltage, low-current circuits which in turn activated large contactors under the car. These contactors were activated in combinations that routed motor current through different sets of resistance grids, thereby controlling motor speed and, hence, acceleration.

The first widely-used Type M system consisted of DB-15 contactors, DB-20 reversers and C-6 controllers designed in 1901 for the electrification of the large Manhattan Elevated system in New York. When the Aurora Elgin & Chicago (predecessor to the CA&E) was built a year later, the most modern MU system available for heavy electric equipment was the system developed for Manhattan. The AE&C wanted four GE 66 motors per car, though, and since the DB-15 contactors were only designed for two of these motors, the early AE&C cars were basically two two-motor cars back-to-back. Each car had two complete sets of contactors, reversers and grids. Car 309, though built five years later after the development of more modern Type M systems, was equipped with the earlier DB-15 contactors - probably because it was fitted with electric equipment at Wheaton Shops, which likely used whatever spare parts they had lying around.
Pictured above is one of the contactor boxes under car 309. Each of the two sets of contactors consists of 13 contactors, carried in three separate boxes. Shown above is the third box for the #1-end contactor set. In the background left is the second box, on which the cover is closed. DB-15 contactors had doors on the arc chutes that could be opened; the two contactors nearest the camera have their doors opened and the two further away have their doors closed. This was an unusual feature of the DB-15 not used on later contactor designs.
Here we see an individual contactor. The arc chute, which was designed to sheild the arc created when motor current was shut off from anything metal that might provide an electrical path to ground, has been painted with red insulating varnish. The contactor is closed by energizing a solenoid, behind the arc chute and next to the assembly frame (1), which raises the contactor arm (2) attached to the lower contactor tip (3) and brings it into contact with the upper tip (4). The motor current passes through whichever contactors are raised at the moment via heavy cables (5). To shut off the motors, power to the solenoid is cut, dropping the contactor arm and separating the contactor tips. The resulting arc is extinguishes safely with the help of a blow-out coil (6) and, on this design, "horns" on the contactor tips (7). During normal operation, the arc chute door (8) is closed to assist in containing the arc.

I also recorded a brief video demonstrating the components and operation of the DB-15 contactor, including interlocks. Interlocks are safeguards incorporated into the design as separate circuits that prevent various bad things from happening accidentally, like activating the reverser while motoring or energizing series and parallel circuits simultaneously.