The tap for the light wiring (although shown otherwise in the drawing) is usually taken off the main circuit before the circuit breaker is reached. This arrangement allows the lamps to be burned when the circuit breaker is open. After passing through fuses and switches in the motorman’s cab the circuit for the lights is led through the car in moulding concealing it.
The wires running between the motors, controllers and resistance frames underneath the car, as has been stated, are often carried in canvas hose. Usually two cables are made up, for should all the wires necessary be placed in one cable this would become too bulky to be properly cleated up. To make the canvas hose waterproof and to prolong its life it is usually given several coats of asphaltum paint.
The wiring of the new cars of the New York subway is an example of the most advanced practice. All the wires under the cars are carried in “loricated” conduit, which consists of a wrought-iron tube heavily enameled both inside and out. The motor leads and the other larger wires are carried in separate conduits. The conduits are usually hung to the steel beams of the floor framing by strap bolts. This method of wiring gives a reasonable assurance that it will not become defective. Moreover, it lessens fire risk. The conduits are all grounded and should one of the wires come in contact with the conduit carrying it, the dead ground resulting would cause the fuse to blow instantly, and all danger would cease.
RESISTANCES.
The type of resistance now most common for heavy motor equipment is in the form of cast-iron grids, which are assembled together and connected in series. These grids are sufficiently stiff to render unnecessary any solid insulation between them, and hence they can radiate heat to the best advantage. The only difficulty experienced with them is from the warping or cracking. Resistances for lighter equipment are composed of sheet-steel ribbons wound in coils. Each turn of a coil is insulated from the next by asbestos. Other forms of sheet-steel resistance with asbestos insulation between the turns, have also been used. In [Fig. 32] is shown a Westinghouse grid type diverter for street railway equipment.
ELECTRIC CAR ACCESSORIES.
Canopy Switch. An overhead switch, sometimes called a “canopy switch,” is commonly placed over each street-car platform where a controller is located, usually in the deck or canopy above the motorman’s head. This is simply a single-point switch that may be used by the motorman to cut the trolley current off from the controller wiring so that the controllers will be absolutely dead. When two such switches are used, one on each end of the car, they are connected in series.
Fig. 32. Grid Type of Resistance.
Car Circuit Breaker. Frequently on large equipments an automatic circuit breaker is provided instead of this overhead switch. This circuit breaker can be tripped by hand to open the circuit whenever desired; and is also equipped with a solenoid magnet, which can be adjusted so that it will trip or open the circuit breaker at approximately whatever current it is set for. This circuit breaker protects the motor and car wiring from excessive current, such as would occur in case of a short circuit in motors or car wiring, or in case the motorman turned on current so rapidly as to endanger the windings of the motors. Circuit breakers, however, are most commonly used on cars having controllers located at only one end in a motorman’s cab.