In conducting a megger test as shown in figure "A" of the illustration, a ground is detected. For testing purposes, how can the motor feeder cable itself be eliminated or confirmed as the source of the ground? See illustration EL-0027.
• To isolate a fault with a megohmmeter (megger), you must test only one component at a time. • The motor feeder cable connects between the starter terminals (T1–T3) and the motor terminals (T1–T3). • Any component still connected in the circuit (starter, overloads, motor windings) can mask or share the ground fault, so they must be considered.
• In figure A, what equipment is included in the megger path besides the motor feeder cable? • What has to be disconnected so that the only thing being insulation-tested is the feeder cable itself, with no motor or starter in parallel? • If you disconnect at just one end of the cable, what is still electrically connected that could still show a ground?
• Make sure the test configuration leaves only the cable between the megger leads and ground. • Verify whether the starter and motor windings are completely out of the test circuit in your chosen option. • Check that, after disconnection, you could perform the insulation test from either end of the same isolated cable and get the same reading.
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