When all is said and done, there is only so much power you can get out of a 13 amp electric socket!
A standard 2x 3-stage vac machine with decent pump is maxxed out on one cable. A twin cable machine can run 2 vacs, pump and heater or 3vacs pump and no heater. Bear in mind a 3KW heater takes up 12.5 amps, so is the only thing that can run on one cable
You would need a 3rd cable to run 3 vacs or more with a pump and heater also running all at the same time. Considering you sometimes can't find one socket in a hallway, it all gets a bit tricky. Considering you quite often trip a house's fuse box just switching on a twin vac machine, what's the point.
If only there was a way of getting high vacuum, airflow, heat and pressure at the push of a button........Dare I say it? Truc..........