HELP EXPLAINING PLEASE

[ROBOJOE77]

We've been troubleshooting a vessel used for heating parts. It uses a DC power supply to provide 45 V at 8000 A. We continue to get a sporadic DC over current fault identified by a mV reference from the negative bus. I recently removed the leads from the power supply to attempt testing the load side isolation to ground as it should be isolated. Using an Ohmmeter I get around 1400+ Ω between each zone to ground. Using our megger set at 50 V, I get 0 MΩ which would lead me to believe that I have bad insulation somewhere in the circuit. How can I explain to our non electrical engineers the difference in these readings, because if I tell them that my resistance reading is showing 1400+, but my insulation reading is 0, they're going to be confused because they are both an Ω measurement.

 

[Elect117]

I am not sure I understand your set up or your testing, but to answer the question:

To explain the difference, I would explain in as much detail, with photos and possibly a drawing what you tested and provide the results. Think of it like a lab experiment and you are trying to prove a case. You should mention things like the first test provide a high impedance value because it measured the circuit sections or parts from X to Y. The second test provide injection current to show that there is a faulted section in X to Y.

Something like that. Make sure it is organized.

If needed, you could look into a local engineering consultant to come and verify the results or help diagnose the issue to provide a more detailed report to management. That usually helps get their attention.

 

[tortuga]

Using our megger set at 50 V, I get 0 MΩ which would lead me to believe that I have bad insulation somewhere in the circuit.

Can you eliminate segments of the circuit to narrow down where the ground fault is?

 

[zbang]

How? You don't ?
1400 Ω = 0.0014 MΩ and can easily round to 0.00 MΩ.

I'd consider testing with a higher current than most digital meters provide, but I think that would simply prove the 1400.

 

[Elect117]

How? You don't ?
1400 Ω = 0.0014 MΩ and can easily round to 0.00 MΩ.

I'd consider testing with a higher current than most digital meters provide, but I think that would simply prove the 1400.

That is the math that NASA used to get to the moon!

 

[tortuga]

How? You don't ?
1400 Ω = 0.0014 MΩ and can easily round to 0.00 MΩ.

I'd consider testing with a higher current than most digital meters provide, but I think that would simply prove the 1400.

for an insulation test I would not test thru the load, I'd be tying all the leads together and testing from the leads to the equipment ground.