The main line circuit breaker, which is electro-pneumatically operated, will open automatically on overload and can be reset by the motorman on all the cars of a train by closing a switch located beside each controller.

CAR HEATERS.

Electric Heaters for warming cars in winter, consist of iron wire coils which are warmed by the passage of electric current through them. The heat so evolved varies as the resistance multiplied by the square of the current. The iron wire coils of the heater are mounted on non-combustible insulating supports, and are arranged so that there is a free circulation of air through them. The coils are surrounded with a perforated metal case, the object of which is to prevent injury to the coils and to prevent persons or clothing coming in contact with the hot, live wires of the coils. Heaters are sometimes arranged so that they can be connected in series or parallel to give different degrees of heat.

The diagram, [Fig. 29], shows the most common arrangement of electric heaters recently. The tap from the trolley should be taken off on the trolley side of the circuit breaker. After passing through a fuse the circuit goes to the switch. Each of the heaters contains two coils, one of higher resistance than the other. Two independent circuits are run from the switch, through the heaters and to the ground. One circuit passes through the high resistance coils of the several heaters while the other goes through the low resistance coils. The switch has three points. On the first point a circuit is made through the high resistance coils. The second point connects the low resistance coils while the third point puts both circuits in service. With this arrangement three gradations of heat may be obtained.

To avoid complicated wiring sometimes but one circuit is employed. In such a case the heat must either be all on or off, no gradations being possible.

The chief difficulty encountered with electric heaters is the breaking of the wires because of the scale of oxide that forms gradually when they are run at a high temperature or because of water striking them from passengers’ clothing on wet days, which causes the wires to snap.

The Consolidated Car Heating Company gives the following data on the current required to heat cars:

Length of Car Body. Amperes.
Switch Positions.

1

2

3
Average conditions 14 to 20 feet

3

4

7
20 to 28”

3

6

9
28 to 34”

4

7

11
Severest conditions 18 to 24 feet

4

7

11
28 to 34”

6

8

14

In his Electrical Engineers’ Hand Book, Mr. Foster gives results of tests made on Brooklyn cars as follows:

Cars. Temperature F. Consumption.
Doors. Windows. Contents cu. ft. Outside. Average
in car.		 Watts. Amperes
at 500 volts.

2

12

850½

28

55

2295

4.6

2

12

850½

7

39

2325

4.6

2

12

808½

28

49

2180

4.3

2

12

913½

35

52

2745

4.5

4

16

1012

7

46

3038

6.

4

16

1012

28

54

3160

6.3