Originally Posted by Protocol.
Induction cooktops use a completely different method of heating. It uses waves of magnetic force to induce heat in another object (pot).
It is more efficient to run an element at 120/240V than at 120V.
5000W element if run at 240V will draw 20 amps (in a perfect world)
5000W element if run at 120V will draw about 41 amps. (once again, perfect world)
It gets a little bit more complicated than that because you are dealing with a single-phase 3-wire system. But it's mainly to provide enough power (watts) while still keeping current low (high current = high line loss)
To add to that....the higher the current...the larger the wire needs to be....
To give you an idea....look at how large the battery cables are in your car. Lets say that your starter pulls 400amps when cranking the engine....that is 4800 watts....
For 4800w @240vac....your wire is now only a #10 awg....a fraction of the size of the battery cable.
Additionally....voltage drop is a big issue....
Wire has a give voltage drop for a given current....assume a length of wire has a 1 volt drop for a given current....at 12 v, that is a good % of your voltage....at 120v, your now down to 119...at 240vac, just 239......hence, the higher the voltage, the more potential work you have available.
That is one of the reasons you see higher volatages for industrial motors...typically 3ph 480Vac...