Growler tester will check only the short circuit [between turns or to Ground] of an armature. Surge tester will check the insulation
state between turns[rotor and stator].It is more complex and needs an oscilloscope.
Growler test might be able to locate short between turns, but only a pre existing dead short...because it's a low voltage test.
In contrast, surge test is a high voltage test, capable of breaking down weak turn insulation to detect it before it breaks down during power system-created surge or mechanical factors in service.
Said another way, surge testing is like a hipot for turn insulation. That can be good because it's sensitive. It also means the test should be planed and considered carefully before performing I it...and only done by qualified people
