prettydresses

As we are talking about electrical safety risks, which with mains power have potentially fatal consequences, I'd suggest only responding if you are either an expert, or don't have much knowledge. People in between these two skill levels, who think they have "enough" knowledge, are the ones who tend to overestimate their skill/knowledge level the most.

Whilst you are right that wire "only cares about current" (in a vast number of circuits which can be modelled simply without taking into consideration things such as skin effect of conductors, etc), there is one VERY important element to cable which ABSOLUTELY cares about voltage. And that is the insulation. YES, cable IS rated for voltage - that means car wire may not have been tested to ensure the insulation doesn't allow higher voltages such as mains, to conduct through the insulation, break down the insulation, or have capacitive effects etc, which would absolutely let the outside of the cable's insulation be live with mains voltages if it were the case.

There's no point talking about protective/safety earthing if you're going to be recommending that 12 or 24 volt DC cable is safe to use on mains voltages. The reality is that unless it's rated for mains, it is unknown whether it will be safe to use.