Sometimes errors are made in connecting the field coils, causing them to act in opposition. This may occur when the dynamo is a new one or the coils have been removed for repairs. It may be caused either through the coils having been put on the field cores the wrong way, or through incorrect coupling up. Under these circumstances, the dynamo, if bipolar, will fail to excite; and if multipolar, poles will be produced in the yokes, etc. It may be remedied by removing one of the coils from the core and putting it on the reverse way, or by reversing its connections. The correctness of connections of all the coils should be verified. In compound dynamos it sometimes happens that the machine will excite properly, but that the series coils tend to reverse the polarity of the dynamo, thus reducing the voltage as the load upon the machine increases. This may be detected when the machine is loaded by short circuiting the _series coils_, not the _terminals_. If the voltage rise in doing this, the series coils are acting in opposition to the shunt coils, and the connections of the _series coils_ must be reversed. Reversed Field Magnetism.--This is sometimes caused by the nearness of other dynamos, but is generally due to reversed connections of the field coils. Under such conditions the field coils tend to produce a polarity opposed to the magnetization to which they owe their current, and therefore the machine will refuse to excite until the field connections are reversed, or a current is sent from another dynamo or a battery through the field coils in a direction to produce the correct polarity in the pole pieces. CHAPTER XXXII ARMATURE TROUBLES A large proportion of the mishaps and breakdowns which occur with dynamos and motors arise from causes more strictly within the province of the man in charge than in that of the designer. The armature, being a complex and delicately built structure, is subject in operation to various detrimental influences giving rise to faults. Many of the faults which occur are avoided by operators better informed as to the electric and magnetic conditions which obtain in the running of the machine, especially the mechanical stresses on the copper inductors due to the magnetic field and the necessity of preserving proper insulation. The chief mishaps to which armatures are subject are as follows: 1. Short circuits; a. In individual coils; b. Between adjacent coils; c. Through frame or core; d. Between sections of armature; e. Partial short circuits. 2. Grounds; 3. Breaks in armature circuit.