The Diseases Of Electrical Machinery

24 THE DISEASES OF where the machines are not insulated from earth, the occurrence of a break in the insulation in one of the loads, if ti ere is at the same time a short-circuit between armature winding and armature iron, may "y result in the destruction of \ the winding. Fig. 3 explains this diagrammatically. fy /C/ A casual connection [ I between the brush-holder 1 T „ spindle and the rocker is Fig. 3 . . in itself of no account until another short-circuit takes place at some second spot. To follow up the direct bearing of these remarks, let it be remembered that a breakdown cannot occur unless or until a wrong path is opened to the current along which it can pass. There must be an entrance and an exit for the current. If there is only one place where the winding and the iron are in contact, the current has an entrance but no exit. So nothing occurs until there is a second contact somewhere else between some live part of the circuit of the machine, or of the leads and the iron of the machine, or some- thing that is connected to the iron. It is not difficult to locate the short-circuit in a machine by means of a galvanoscope or simple galvanometer, such as a common linesman’s detector and a single Leclanché cell, or a “dry” cell. If no galvanometer is available, an ordinary electric beil