I am not sure if this has anything to do with this thread, but I have found that HF really seems to get around. I have an add-on HF box, and when I turn it on, the GFI to the workbench outlet always trips. It will trip the GFI even when it is not plugged into the GFI outlet. Even if it is plugged into a circuit on another breaker, it will trip the GFI. But, if I unplug all power cords from the GFI outlet, it will not trip the GFI. I added an industrial strength line filter inside the HF box, and the results are exactly the same. That means that the HF is not getting out through the power line, and it is not radiating from the HF box line cord. I then tried keeping the welding leads closer together, and there is more power in the HF spark, but still, it trips the GFI if anything is plugged in. Also, any lights on flexible power cords (not in conduit), flash when the HF is on, regardless of circuit that they are plugged into.
This indicates that the HF is behaving like a radio wave, and the AC impedance to ground of the lighting circuits is much smaller than the DC impedance. The HF will even make a halogen lamp (big) flash. The reason for this is that the HF box is not a simple transformer. It is more like a tesla coil, and the HF bursts are in the range of several amps at thousands of volts. This is what makes them so damaging to electronics. If they make a large halogen floodlight flash, which is plugged into a different socket, they are pretty potent.
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