=Ques. For what kinds of service are series motors unsuited?=
Ans. Series motors should not be employed where the load may be entirely removed because they would attain a dangerous speed. They should not be used for driving by means of belts, because a sudden release of the load due to a mishap to the belt would cause the motor to "run away."
Very small series motors may be used with belts since their comparatively large frictional resistance represents an appreciable load, restraining the motor from reaching a dangerous speed.
=Ques. For what service are series motors adapted?=
In the case of a sudden release of the load the gears provide some load on account of the frictional resistance of the gear teeth.
[Illustration: FIG. 418.--Shunt motor connections. A shunt motor runs at constant speed on a constant voltage circuit. In connecting the motor in circuit, the field coils must be placed in circuit first, so that there is a certain amount of field strength to produce rotation of the armature and thus prevent excessive current through the armature. If the field magnets were not put in the circuit first, the armature, at rest on receiving current, would probably burn out, because it is of low resistance, and would take practically all the current supplied, especially since no reverse voltage is generated in the armature at rest. The method of starting is shown in the illustration. To start, the switch is closed, and the rheostat lever pushed over so as to make contact with A and B, thus _first_ exciting the magnets. On further movement of the lever, the rheostat resistances R, R_{ 1}, R_{ 2}, R_{ 3}, etc., are gradually cut out as the speed increases, until finally all the resistance coils are cut out. To stop, the lever is brought back to its original position.]
=Ques. What advantage is obtained with series motors with respect to the connections?=
Ans. A single wire only proceeds from the rheostat to the motor, so that, with the return wire, only two wires are required.
=Ques. For what service are series motors specially adapted?=
Ans. Series motors are used principally for electric railways, trolleys, and electric vehicles, and similar purposes where an attendant is always at hand to regulate or control the speed. They are also used on series arc light circuits in which the current is of constant strength. Very small motors are generally provided with series windings.