- Grounded controller blow-out coil.
- Grounded trolley wire or cable.
- Grounded lightning arrester.
The blowing of the fuse immediately on closing the overhead switch or circuit breaker, when the controller is on the off position, indicates that the fault exists somewhere between the overhead and the upper or trolley finger of the controller.
Should the defect occur during a thunderstorm, it may be presumed at once that lightning has grounded the blow-out coil of the controller.
CASE II.
Fuse Blows on first point:
- Grounded resistance near R 1.
- Grounded controller cylinder.
- Bridging between sections of cylinder.
When the controller is on the first point all of the wiring of the system with the exception of the ground wire for No. 1 motor is connected with trolley. But a defect in the wiring beyond the resistance will not show itself on the first point by an abnormal rush of current because the resistance of the rheostats is sufficient to prevent any excessive flow of current.
Fig. 101.
