MCC Low Megger Reading
MCC Low Megger Reading
(OP)
We were taking megger readings (phase to ground and phase to phase) for an MCC before first-time energization, and the results that we're getting were below 1.0 gega ohms. All the other MCC's on site registered greater than 2.2 gega ohms for the same test. We noticed that once we start pulling out buckets one by one the megger reading started to increase. Eventually, the megger reading was greater than 2.2 gega ohms when about half of the buckets were pulled out. Do you know what could be causing this current leakage and how we can fix it? Thanks





RE: MCC Low Megger Reading
RE: MCC Low Megger Reading
RE: MCC Low Megger Reading
RE: MCC Low Megger Reading
RE: MCC Low Megger Reading
I don't see anything in the E3Plus manual that would indicate that it would be a problem but it is a self powered solid state device.
If the readings change with the disconnect position then you know that the problem is after the disconnect. You could remove an E3Plus and check the resistance between phase leads.
If that doesn't narrow it down or solve your problem then I would contact A-B.
RE: MCC Low Megger Reading
RE: MCC Low Megger Reading
If they were similar sized MCCs in similar environments then I would contact A-B about their recommended test procedure and minimum test results.
RE: MCC Low Megger Reading
Come back when you have resistance values in the 1Mega ohm range and we can talk. Accurately measuring resistance values in the Giga ohm range requires precision equipment, controlled environmental conditions and a skilled technician.
RE: MCC Low Megger Reading
We initially thought that there could be some moisture in the MCC, so we directed warm air from a unit heater inside the MCC bus and left the starter buckets open. The megger reading was taken and it was even lower than before, around 300 M-ohm (which doesn't make sense to me). We kept the heat running for 24 hours and the reading stayed the same. Then we removed the heat, waited few hours, and the reading went up to 700 M-ohm.
I hope this helps. Thanks again!
RE: MCC Low Megger Reading
RE: MCC Low Megger Reading
RE: MCC Low Megger Reading