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From UL standard, if I only want to measure a part of device's leakage current to another part. I can just measure the Grounding wire. So I used a clamp on meter (0-10mA range) to clamp on grounding wires. In the cases below:

  1. Ground the motor and driver together, and measure at driver side grounding wire to the power device. I assume this will give me the total leakage.
  2. Unground the motor and driver, and measure at the driver side grounding wire. I assume this will give me the leakage of driver only
  3. Unground the motor and driver, and connect a grounding wire from motor chassis to the power device grounding. Then use clamp on meter to measure on it. I assume this will give me the motor only leakage.

But I found the sum of leakage of motor only and driver only does not equal to the total leakage. Does anyone know why? Or it is not the sum up relationship?

I used a AC power supply to do the testing. I found it gives way less leakage current reading than I use a variac. So I think the varic has some leakages too but I don't know if it is the AV power supply has some filters?

I used below connector to connect wires to the power device. Why do I get different reading on both side of the wires? I am so confused.

enter image description here

enter image description here

I am saying additional grounding wire is because the driver's power input only has line and neutral. The grounding wire doesn't go "on board". So I clipped it on metal chassis. Hope the new picture is helpful to understand.

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    \$\begingroup\$ If you could draw a diagram, that would be helpful. \$\endgroup\$ – P2000 Jun 23 at 23:40
  • \$\begingroup\$ @p2000 Just did. \$\endgroup\$ – Rae Jun 25 at 14:59
  • \$\begingroup\$ Ok great. I won't be able to answer the question, but hopefully this will get you some more qualified views. You can also embed the image into the post, rather than by linking it to imgur. \$\endgroup\$ – P2000 Jun 25 at 18:14
  • \$\begingroup\$ "But I found the sum of leakage of motor only and driver only does not equal to the total leakage." - Why would you expect them to? And the values you measured were? \$\endgroup\$ – Bruce Abbott Jun 25 at 19:47

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