Use for "suicide cables"?

All you need is an interlock kit. Will cost you $50-$150, depending. Pretty cheap compared to what you must have already spent. An interlock kit would make what you have legal, probably.

A variation on the suicide cable- mains plug on one end, and RCA (phono) audio connector on the other, wired between live and neutral.

I have no idea at all why someone constructed this. I have never been able to think of an even half-plausible reason, but I do know it melted the internals of a very expensive Revox tape recorder.

That’s the thing. In a pinch, when the house is approaching 35 degrees F, you’ll do what you must. And I wouldn’t really fault someone for that. Done right, this is sub-optimal but not outright stupid, IMO.

Now, if they didn’t have the sense to kill the main breaker, then they shouldn’t be messing around with it at all. But if I were facing frozen pipes and that’s what would get the furnace running, well…

(Incidentally, living where I do I have got a portable generator with appropriate, code-compliant transfer switch and cables. But the first time I was out for a week I was in a similar situation and did what I had to. In my case I shut off the main breaker and used the 200’ of romex I had lying around and wired directly to the critical systems like well and furnace, first disconnecting those systems completely from the system. It was rube goldberg but safe)

I made and used one, once. Power was out so I borrowed a small generator from a friend. It had only sockets and our house had no special wiring.

Luckily our outdoor plugs were on the same rail as the fridge, so I disconnected the main, turned off all other circuits but outdoor & fridge, plugged the generator in outside, and started it up.

It pained me to make the suicide cord (though I never heard the term until now.) I made a point to tell my wife and son about the danger & to keep clear. The plugs fit snugly and the generator was right next to the outlet so there was little danger of an accidental unplug.

Worked great, no accidents. It did bug the heck out of me, though!