Hi James,

I will start with the ground leakage meter. Most of the time the harmonic filter makes a small difference in the current reading. What the meter does do that makes a big difference is it has what appears to be a zeroing algorithm. When the meter it is initialized it shows a value above zero that slowly steps down to zero in a few seconds. The zero button is intended for relative measurements. I have used the zero button in a really big field to stabilize the reading.

I think AC zeroing might solve my problem with the mooshimeter. Being able to reject ac field noise would allow a magnetic pick up that outputs in millivolts to give accurate readings. This is more important for power functions because it would affect power factor calculation. (The noise is not likely to be in phase with the current.)

I my particular case I use power (KW) to watch pump performance under different flow conditions. If I only used current I would see little or no difference in the current on a single phase pump because the power factor changes relative to the load.