> the cost of sensing large AC current. That’s very cheap and
> has been for a long time.

Cheap relative to the cost of an ordinary duplex outlet? $1.69 at Lowes. If I wanted to nitpick, I'd say since the outlet is duplex, TWO sensors need to be cheap compared to $1.69.

> You simply place a loop around the conductor and that induces
> a smaller current in the loop proportional to the current in
> the main conductor.

It sounds like you are describing a current transformer, but thats not how they work. You place a closed magnetic core (ferrite or iron-powder toroid, or steel laminations) around the wire, and then wrap many turns of wire around the core. If you have 500 turns of wire around the core, then the current in that winding is 1/500 of the main current.

If you are describing something else that exists today, please let me know (point me to a supplier's website or something). I use current sensors of all sizes, and would like to know if I'm missing something.

Iron cores and wire windings don't benefit from semiconductor scaling, so even with automation there will be some minimum cost to make such a transformer. An alternative technology would be a semiconductor Hall sensor near a conductor. If the geometry of the conductor and sensor are known and fixed, you can scale the Hall output to get current. As time goes by, Hall sensors and the associated circuitry _will_ get cheaper.

> I think the main application in large-current devices would be
> when running on reduced power (backup batteries) or alternative
> power (solar) where you must be much more careful about load.

Granted. I would claim that those are the "niche" applications where I said such technology could offer benefits that outweigh the price penalty. I just don't see it happening on a wide scale until the total cost is less than $1.00 per outlet, and I don't see that happening for quite a long time.

I must admit that I'm biased, because I make my living figuring out what can be designed, built, and sold over a time-frame of a couple of years, using today's technology. You are looking farther out, and considering things that might need breakthroughs to be practical. Differnet world-views.

Interesting concepts in any case.