One controller may be defective in that one of the contact fingers may not make connection with the drum. In this case try the other controller if there is another one on the car.
The fuse may be blown or the circuit breaker opened. The occurrence of either of these, however, is usually accompanied by a report which leaves little doubt as to the cause of the interruption in current.
The lamp circuit is always at hand for testing the presence of current on the trolley wire or third rail. If the lamps light when the lamp circuit is turned on, it is a tolerably sure sign that any defect is somewhere in the controllers, motors, or fuse boxes, although in case the cars are on a very dirty rail enough current might leak through the dirt to light the lamps, but not sufficient to operate the cars. In such a case, the lamps will immediately go out as soon as the controller is turned on. Ice on the trolley wire or third rail will have the same effect as dirt on the tracks.
LOCATING DEFECTS IN MOTOR AND CONTROLLER WIRING.
Defects in the wirings are those due to (1) open circuits, (2) short circuits. Open circuits make themselves evident by no flow of current, short circuits usually by a blowing of the fuse or opening of the breaker. The point of the short circuit or “ground” can be located roughly by noting on what point the fuse is blown. Accurate location can be made by cutting out the motors, disconnecting, etc., according to directions in the following pages. The tests outlined apply particularly to the K type of controller with two-motor equipment.
OPEN-CIRCUIT TESTS.
No current:
On 1st point,
Open circuit but not located.
On 1st point multiple,
Motors most probably O. K.
On series-resistance points after trying 1st point multiple,
Open circuit outside controller and equipment wiring.
With an open anywhere between trolley and ground no current will flow on the first point. Opens are most likely to occur in the motors and these may be tested first. However, as will be explained later, one open in an armature will not stop the current. To test the motors open the breaker and put the controller on the first point multiple. Then flash the breaker quickly. Current flowing indicates that one or the other of the motors has an open circuit. In the series position this open prevented the flow but in multiple the current flows through the other motor. Which one is at fault can be quickly determined by returning the controller to the off position and cutting out one or the other of the motors by means of the cut-out switch and then trying for current. The car can in any event be run on the remaining motor. On returning to the shop the open can be determined definitely by the use of the lamp bank.
But should no current flow when the breaker is flashed on the 6th point it is reasonable to presume that the motors are O. K. and that the open is elsewhere. The ground for such a supposition is that as there is a path through each motor normally, there would necessarily be an open in each one to stop the current. It is hardly probable that such a coincidence would occur.
After failure to find fault with the motors, doubt as to the resistance may be removed. The controller should be placed on progressive series-resistance points and the breaker flashed on each one. If current is obtained on any point, the open is in the resistance or the resistance lead just behind the one being used. Special care should be used to flash the breaker quickly for otherwise the fuse may be blown.