The tests indicated are sufficient for the motors, controllers and resistance wiring. If no current is obtained on either of them, the trouble is evidently caused by a bad rail contact, ground wire off if both motors are grounded through the same wire, an open in the blow-out coil, at the lightning arrester, circuit breaker or on top of the car.

None of the tests applied locate the open definitely, but this can easily be done in the shop or wherever a lamp bank is at hand. Connect one terminal of the lamp bank to the trolley just behind the circuit breaker and the controller on the 1st point series, then with the other terminal begin at ground and trace backwards up the circuit until the lamps fail to light. The path in a K type of controller is readily traced with the help of [Fig. 22].

SHORT-CIRCUIT TESTS.

The location of short-circuits is much more tedious. The blowing of the fuse or opening of the breaker will locate them as shown below. The separate tests can then be followed until location is definite.

These tests it must be kept in mind are more especially adapted to cases on the road or where no facilities for testing are at hand.

Rather than blow fuses as frequently as indicated it would in most cases be better to place a lamp bank across the open circuit breaker and note the flow of the current by the lights.

Fuse Blows:

  1. When overhead is thrown on may be due to:
    1. Grounded controller blow-out coil.
    2. Grounded trolley wire or cable.
    3. Grounded lightning arrester.
  2. On first point:
    1. Grounded resistance near R 1.
    2. Grounded controller cylinder.
    3. Bridging between the insulated sections of cylinder.
  3. Near last point series:
    1. Grounded resistance near R 3, R 4 and R 5.
    2. No. 1 motor grounded.
  4. Near last point multiple:
    1. No. 2 motor grounded.
    2. Bridging between lower sections of cylinder.
    3. Armature defective.

CASE I.

Fuse Blows when overhead is thrown on: