When the train is shut down for the night or whatever, and power sources switched off, it relies on the hand brakes being set or the service brakes defaulting to at least a partially applied state or chocks in place at the wheels or friction between the wheels and other related moving parts, bearings, etc. to prevent rolling downhill. The deadman control and reverser key do nothing.
In the 2015 (was it that long ago?) incident with the runaway Red Line train, the holding down of the controller handle other than with the operator's hand is the same thing as (is called) rigging it.
Modern transit cars have low voltage control circuits. Older "conventional" equipment (for example with K controllers) have all 600 volts of traction power below the controller handle. Also up to 600 volts measurable everywhere a circuit is broken such as at a switch in the off position or at a burned out light bulb. This sometimes unexpectedly high voltage as measured by a sensitive meter, drawing just a few milliamperes, is called open circuit voltage.
With DC traction power, motor generator sets (rotary converters) were commonly used before solid state voltage converters were developed, that is before about 1960, to provide low voltage to keep on board batteries charged. This also isolated the control circuits from 600 volt power. I am not sure whether low voltage, say, 32 volts, may have been derived using series circuits including lighting circuits. If an incorrect bulb were used as a replacement then the battery charging subcircuit could give off incorrect voltage and possibly result in a battery explosion.
Last edited by Disney Guy on Thu Jun 23, 2022 6:14 am, edited 2 times in total.
Build something. Anything.
