Insulation Test

—The object of this test is to ascertain whether the insulation of a circuit or of the wire wound upon a metal spool or core, such as a magnet core, has broken down or is still in good order. In making the test, one terminal of a battery is connected to a galvanometer terminal. The unconnected terminal of the battery is connected to one end of the coil under test, the other end of the coil remaining free and unconnected. Some portion of the metal core, say the end, is then cleaned bright with a knife or emery cloth, and the unconnected termmal of the galvanometer is brought into contact with this bright or clean part of the core. If then some portion of the insulation of the wire has been abraded or destroyed, thus bringing the bare wire into contact with the metal core, the needle of the galvanometer will be deflected since a closed circuit is formed through the core and wire. If on the contrary the insulation is perfect, the needle will be undeflected. oy It will thus be seen that in the conductivity test it is nece ary that the needle should be deflected, or turned, to prove that all is right; while in the insulation test the converse holds good, if the needle is deflected it proves that the insulation is broken down.