Actually, there is NO ham interference - they would be used in electrical lines that are inside metal conduits.
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Actually, I have not seen any household wiring within metal conduits, or street three phase cables. Look around and check out the tests.
I don't know how you can train RF to travel along a unshielded cable without radiating as an antenna. If you crack that one let me know.
I actually said hams consider it interference. Despite homeplugs being notched at amateur frequencies, emissions are still above EEC EMC specs. More importantly, there are many other users of the spectrum that don't have the benefit of notch filtering.