C-H,
The thing that you talking about, is called a pre-heater, all Emergency service vehicles over here use them to keep the engine block and oil warm.
I remember one of these nearly burning down the Fire Station in Timaru, when it shorted,the oil was boiling,I noticed it when going outside for a cigarette.
On the subject of 400V, a guy rang me up at home one Saturday morning, said that the rings on his range were too hot, long story short, he had remodelled his own Kitchen and had moved his stove, I went and had a look, Two phases, no Neutral, no Earth wire either!, some people should never be allowed anywhere near Electricity. [Linked Image]