Specifications

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6.4 INSULATION RESISTANCE TEST : With a bar copper wire, short all the commutator
segments, as shown in Fig. 6.14.
Test the insulation resistance between the body and the commutator or segments by a
500V Megger, for armatures rated upto 250 volts.
The IR so measured shall be greater than 1 mega-ohm. If the value is less than 1 mega-
ohm, moisture in the winding or a weak insulation is to be suspected. This test is sometimes
conducted by a series test lam and is called the ground test. It will only indicate if any coil is
grounded, and not the insulation resistance.
Fig. 6.14
6.5 GROWLER TEST : A simple and most common method to test armature winding for short
and open coils is by a growler. There are two types of growlers. 1) Internal growlers 2)
External growlers.
An external growler is used for testing small armatures and an internal growler for large DC
armatures and AC motor stator windings.
External growler
Fig. 6.15